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 PHOTO-LITHOGRAPHY

 [Illustration]

 BY

 GEORG FRITZ

 _Vice-director of the Court and Imperial State Printing Works at Vienna_

 TRANSLATED BY

 E. J. WALL

 (_Fellow of the Royal Photographic Society_)

 _Author of “The Dictionary of Photography,” “Carbon Printing,” etc._

 [Illustration]

 1895
 LONDON
 DAWBARN AND WARD, LIMITED
 6, FARRINGDON AVENUE, E.C.




THE AUTHOR’S PREFACE.


Photo-lithography, with its many branches and its extended application,
when used direct and also as handmaid for the lithographer and printer
from stone, is, with the exception of phototypy and autotypy, indeed
that process for the preparation of letterpress plates which has done
the most towards making photography useful for the graphic arts, in the
artistic sense as well as from the practical point of view. And in the
near future it will be a great acquisition when it is once generally
recognized that colour plates can be prepared by photographic means
without any considerable amount of manual or artistic help. It is the
more to be wondered at that photo-lithography has not yet found that
extension and general use which it in so high a degree deserves.

I have written this book, impressed with the urgency of stimulating
the propagation of this useful process. In writing I have been careful
to avoid all those details which are for the practical worker of
minor interest—the description of the historical evolution, etc., so
instructive as these must certainly be—so that I have abstained from
many complicated and unintelligible formulæ. I leave this willingly to
a more ready writer. Starting rather from the standpoint of speaking as
a practical worker to practical men, I have recorded all the experience
which I have gained in the course of many years.

Should it occur to me in the future that it was my task to have treated
all photo-lithographic processes, with all their ramifications, in
the most complete manner, I have still the consciousness of having
described as completely as possible the practical processes, and think
that I have thus been useful to many workers, {2} and I dare say with
absolute certainty that only tested and tried formulæ have been noticed
in this book.

With the earnest wish that this book may be received with a fraction
of the goodwill with which I have worked at the writing of the same, I
present it to the technical world.

 GEORG FRITZ.

 Vienna.

       *       *       *       *       *

On receiving this work for review I was greatly struck with the
thoroughly practical manner in which it was written, and thought that
an English translation might be acceptable to the large and ever
increasing class of photo-mechanical workers who might not otherwise
have the opportunity of reading it in the original. I have kept to the
author’s text as close as is consistent with the idiomatic construction
of German.

I am indebted to Messrs. Hazell, Watson and Viney for permission
to undertake the task of translating the work for another firm of
publishers, and I hope the translation may prove as acceptable and
useful to the readers as it has been pleasurable to me to do it.

 E. J. WALL.

 1, Creed Lane,
 London, E.C.

{3}




INTRODUCTION.


1.—_The theory of printing from stone._ He who would study or practise
photo-lithography must first become acquainted with the fundamental
principles on which lithography rests. I find it therefore necessary
to first give in concise form a small treatise on the theory of this
process as well as on the most important materials which are necessary
in the practice of the same.

The theoretical principle of lithography is purely chemical, and is
based principally on the repulsion of water and other substances by
fatty bodies, and the alteration of these greasy bodies by acids. As
the support for this chemical opposition a stone or zinc plate is used,
which are sufficiently porous to allow grease, water, acid, and certain
resinous solutions to penetrate to a certain degree.

The fatty substances which are transferred to the stone by writing,
drawing, or transfer, are autographic ink, lithographic ink, and chalk,
the so-called transfer and photo-lithographic colours. There are also
other substances, which are used especially in photo-lithography, which
do not evidently penetrate the stone and which cannot be considered as
greasy substances, but which, as we shall see later on, have exactly
the same action.

The above-mentioned fatty substances actually penetrate the porous
stone and make it in places suitable to take more printing ink. By
the so-called etching—dilute nitric acid mixed with gum water—two
effects are produced. On the one hand the fatty bodies are altered
in chemical composition, being decomposed into the fatty acids which
combine intimately with the material of the stone—calcium carbonate.
On the other hand, the surface of the stone not covered with the
fatty substances is chemically changed, since the carbonate of lime
is converted into nitrate, which has now the property of keeping
moderately damp when moistened with water, and thus repelling grease.
If such a transfer of greasy bodies on to the stone is allowed to act
for some hours, and the fatty substances are removed with turpentine,
it will be seen that these places have a lighter colour than the other
parts of the surface of the stone, and if the stone be rolled up with
a leather roller, charged with a greasy ink, after the stone {4} has
been damped, only these places will take the greasy ink. By means of a
litho steam or hand press prints can then be prepared from this.

It is frequently necessary to make corrections or additions to the
drawing on the stone; if the stone has been already etched some means
must be used _which will remove the action of the etching_, or else the
stone will not take the greasy matter, or at least not so readily as is
desirable. Very weak acetic acid, about 1–2 per cent., will do this. If
the stone is flowed over with this dilute acetic acid or dilute table
vinegar, the action of the stronger nitric acid and the gum is stopped,
and the surface of the stone will again take fatty matter.

Before the penetration of the grease the stone is prepared by polishing
with a concentrated solution of oxalic acid. Oxalic acid poured on
to the stone would exert an etching action, but make the stone to a
certain degree capable of taking the ink. If this liquid is rubbed on
the stone with a cloth or linen pad with moderate pressure, the stone
receives a high polish—especially the hard kinds—and in this condition
the stone takes the ink well, like any flat object, but will not retain
it. If a transfer is made on to such a stone, and the same etched, the
image will completely disappear the first time the roller passes over
it. This polish can be removed with 1 or 2 per cent. acetic acid, and
the stone then has its primitive qualities. This method is used to
reverse the image, which will be described later on.


2.—_Litho stone_ is dense limestone of the mountain limestone group,
and is found in the Tertiary deposits at a depth of two to three
metres. Its constituents are lime, clay, and silicious earths, combined
with carbonic acid, but lime is in the preponderance; it only contains
a very small proportion of silica. In the stronger acids litho stone
dissolves completely. The varieties of very fine stalactitic chalk
of tolerable hardness, with flat shell-like fracture, without rust
spots, glassy crystals or impurities, and those with very even grain,
are the most useful for photo-lithography. Marble, which consists of
pure chalk, cannot be used for lithography because, on account of its
greater density, the greasy matter cannot penetrate so deeply, and
therefore such stones would give only a few pulls.

The commercial litho stones are of different colours, from whitish
yellow to greenish shining grey. The latter has a finer and more even
grain, and is considerably harder than the other kind. These two kinds
are briefly designated in the trade as “yellow” and “blue,” and the
brighter kinds are, as a rule, softer and cheaper than the darker.

The faults which the stones sometimes show differ considerably,
and these produce certain inconveniences in continuous work. Many
stones have dark and light spots, and as these spots have, as a rule,
different densities, the etching solution cannot exert the {5} same
action over the whole of the stone, and consequently in fine drawings,
autotypes, etc., there are formed bright and dark spots. This also
occurs with calcareous, speckled, and marbly stones. The very bright
stones have less density, and therefore suck up the damping solution
very quickly, and begin with repeated printing to become tinted. Stones
with calcareous, rusty or other veins split easily, especially in the
large sizes. Lime spots or lime veins, which are easily recognized
by their brighter colour, take in graining a very unequal grain. The
drawing is darker on these places, since the grain is greater according
to the softness of the stone. Such stones are unsuitable for those
photo-lithographic processes in which graining is used, such as the
processes of Orell and Füssli and Bartös. The so-called glass veins and
glass spots are crystallizations consisting of silicon, and are harder
than the other parts of the stone. On these places the fatty inks do
not penetrate deep enough, and the drawing does not adhere well, and
can be easily removed by the rollers.

The hard stones receive a much finer surface than the soft when
polished with pumice stone; they also reproduce every point, line, and
detail of the drawing much more delicately, finer, and sharper; and,
lastly, they have the advantage that they etch much more evenly, and
re-etching is easy if moderate care be taken.

For the finer photo-lithographic work, if quality and continuous
working is desired, only the good “blue” stones should be used; for
cheaper line drawings “yellow” stones free from faults may be used.


3.—_The zinc plates_ are now coming into pretty general use instead of
stones, especially in large establishments. Although their treatment
before and during printing is essentially different to that of the
stones, yet so far as regards this method of printing they come very
nearly equal to stones. At first smooth polished zinc plates were used,
but in consequence of some difficulty in using them, and the great
care necessary in choosing them, they have been almost replaced by the
prepared or oxidized plates.

Zincographic processes differ essentially in the preparation of the
plates. In the one, the plate is given a coating which has a similar
composition to a litho stone; in the other, the plate is roughened and
given a fine grain by a mechanical method, such as the sandblast, in
order that it may be then oxidized by a chemical process, with acids
or alkalies. All these processes are more or less advantageous. The
zinc plates cost about one-tenth to one-twentieth of the cost of the
stones, and this may well be sufficient grounds for the proprietors of
large establishments being interested in zinc plates, as the stones are
rather costly.

Excellent zinc plates, coated with a film or merely oxidized, can be
procured commercially in Germany and Austria. For those {6} who wish
to prepare their own plates the following tested formulæ are given:—

A zinc plate from 1 to 1·5 mm. thick is roughened by means of the
sandblast till it has a fine, even grain and appears smooth, but clean.
The following solution is prepared:—

 Concentrated solution of alum  20 parts
 Phosphoric acid                 2 parts
 Water                          20 parts

or

 Alum solution                  10 parts
 Gallic acid                    15 parts
 Nitric acid                     2 parts
 Water                          30 parts

The roughened plate is first flowed over with water, and immediately
afterwards, with one of the above solutions, in the same way as a
plate, is covered with a developer. The plate is oxidized by this, and
there is formed on the surface a white precipitate. It is then washed
thoroughly under a rose tap and dried, and the plate may be either
coated with a light sensitive substance for printing or a transfer be
made on to it.

After the development or the transfer, the plate is gummed and then
etched with an etching solution consisting of—

 Gallic acid                    10 parts
 Phosphoric acid                 2 parts
 Gum solution                   10 parts
 Water                          30 parts

this being allowed to act for 30 or 40 seconds.

For repeated printing one to two per cent. of gallic acid is added to
the damping water.

If the plate has been correctly treated the print or the photo-litho
transfer will furnish thousands of good impressions, just like a stone.
Further details as to the printing on the zinc plates, or the transfer
of the chromated gelatine prints on to the same, will be found in
Chapter IV.


4.—_The greasy drawing materials_ which are necessary for lithography
are litho tusch, autographic ink, and fatty chalk.

The two first are used in the liquid state, the chalk, however, in
solid form. The ink can be obtained in a liquid form and the two
others in solid state. All three materials consist principally of
soap, tallow, wax, resin, and soot. Soap and tallow give the necessary
grease, wax and resin give hardness and consistency, and soot the
colour. The proportion of grease in the drawing materials must be
so great that even the finest lines or points of a drawing can be
well transferred to the stone, so that they may not be attacked by
the proper etching solution, and do not break away from the stone by
continuous printing. As much black as possible in the drawing materials
is pleasant for the draughtsman, but is not actually necessary for
this particular purpose. {7}

The tusch must dissolve well in distilled water and flow fine and
clean from the pen. It should be tolerably brittle, and the fractured
surfaces should be shiny. The photo-lithographer will frequently
require the lithographic tusch for additions or for corrections. The
best is the so-called Lemercier’s tusch, which is used in nearly all
works. It consists of—

 Yellow wax                      2 parts
 Mutton tallow                   2 parts
 Marseilles soap                 6 parts
 Shellac                         3 parts
 Lamp black                    1–2 parts

These ingredients should be melted together by boiling.

The autographic ink is, as a rule, used for drawing or writing on
paper, and the result is then transferred to the stone. Instead of
this, any litho tusch can be used, but for some work the autographic
ink is more advantageous. This ink must be thin, run easily, but not
patchily, from the pen, and must keep for a long time equal in quality
and action. It is very advantageous that specially-prepared paper is
not required, since this always makes the work more difficult; firm,
hard writing-paper is quite good enough for this work. The commercial
inks generally possess these good qualities, and if much is not
required one will hardly care to prepare it oneself. A good successful
autographic ink which draws in brown may be obtained from the following
formula:—

 Marseilles soap                10 parts
 Tallow                         10 parts
 Shellac                        12 parts
 Yellow wax                     12 parts
 Mastic                          5 parts
 Asphalt                         4 parts
 Vine soot                       3 parts
 Distilled water               125 parts

Originals prepared with this ink transfer as well immediately as after
several months, and ordinary well-sized writing paper can be used for
drawing or writing on.

Lithographic chalk is only prepared in the solid form for drawing on
paper direct or on stone. According to the nature of the work, it is
harder or softer, fatter or leaner. The hard kinds, which are also
usually leaner, contain more resin and less fat; the soft, on the
contrary, more grease.

Fatty chalk is composed of—

 Wax                            30 parts.
 Marseilles soap                24 parts.
 Tallow                          4 parts.
 Shellac                         1 part.
 Lampblack                       6 parts.

{8}

Lean chalk is composed of—

 Wax                            12 parts.
 Marseilles soap                 8 parts.
 Tallow                          2 parts.
 Shellac                        10 parts.
 Lampblack                       4 parts.

For lithographic work a greasy ink is required in contradistinction to
ordinary printing ink, which consists of linseed oil and lampblack,
which would be called “lean.” For inking-up a photo-lithographic
chromated gelatine print such an ink cannot be used. In order to obtain
a good result in transferring, this ink must contain grease, soap, and
resin.

Any good transfer ink can be used for a developing ink, as this
is applied with a roller. It usually consists of equal parts of
tallow, wax, soap, some resin, and as much litho ink as all the other
ingredients put together.

That prepared by C. Kampmann, Technical Instructor in the K.K.
Lehr- und Versuchsanstalt at Vienna, contains, besides the above-named
ingredients, asphalt and gum elemi, and works well in practice.

Thin developing inks, which are distributed with a broad brush or
a pad, can be prepared by diluting good transfer ink with equal
quantities of wax, benzine, and turpentine.

A good developing ink must have the following properties: When spread
upon the print must give a clean, sharp, sufficiently dense impression,
which can be easily transferred to the plate or stone; on the other
hand, the drawing ought not to spread. The transfer should possess such
resistance that, without rolling up, it should resist a slight etching.


5.—_The behaviour of asphalt on stone or zinc._ When a stone or plate
is coated with asphalt solution and exposed under a negative, and then
washed with turpentine, the exposed parts remain insoluble, and in
this way photo-lithographs can be prepared. The asphalt here takes the
place of the fatty ink, and is, after printing, so firm and hard that
without any rolling or inking up it can be etched with a weak, gummy,
etching solution, which gives a cleaner, sharper drawing than the
other processes. The asphalt and other light sensitive resins not only
intimately combine with the stone or plate, but chemically alter the
surface of the stone, and possibly in a more advantageous way than the
greasy inks. When a properly-exposed drawing on stone is, immediately
after printing and development, treated for a long time with rectified
or Neustadt turpentine, it is completely removed from the stone, and
it will be found that the drawing appears of a somewhat lighter colour
than the rest of the surface of the stone. If this is now inked up with
a roller, these places take up the ink _without having previously come
into contact with grease_. Numerous experiments which I have made on
various lines go to show that the {9} chemical theory of lithography
has found an important enlargement with the use of asphalt.

The following are principal conclusions to be drawn from my
experiments:—

(_a._) The exposed asphalt, whether this exposure is made by printing
or whether a drawing is first made and then exposed to the light,
adheres more firmly to the stone or zinc plate than if it was not
exposed. An asphalt drawing prepared in the dark and inked up does
not adhere to the stone, and this may be explained in that the grease
cannot act through the asphalt film. Insensitive asphalt behaves in
the same way. With correct exposure under a clear negative of about 20
degrees Vogel, and subsequent development and auxiliary exposure for
about half to one hour, the drawing adheres firmly to the stone. If
the image is to be washed off, the turpentine must act for five to ten
minutes on the film, till the exposed asphalt has dissolved. If, after
washing off, it is inked up, all the places take the ink well, and
the image appears clear and plain. The image can only be destroyed by
strong acids or alkalies, which actually dissolve the stone itself.

From this it is clear that the prints neither require inking up nor
strengthening in any other way, and my experiments have proved that in
all cases the prints are, by this treatment, clogged up, and neither
gain as regards a longer run nor in withstanding etching.

(_b._) Solution of asphalt, to which oil has not been added, behaves
as described above; if, however, oil is added to it, it acts still
better as regards the keeping of the drawing, and the prints need no
subsequent exposure. Too large an addition of oil has the disadvantage
that, in developing with turpentine, the asphalt dissolves too quickly.
The images wash off and one hardly has time to examine. The exposed
asphalt, to which oil has been added, also dissolves very readily. For
the preparation of colour plates this point is of some importance.


6.—The etching and preparing solutions are those solutions which make
the stone suitable or unsuitable for taking the grease or water.
Generally these are acids and gum arabic, either used alone or together.

Of the acids the most important is _nitric acid_, the purpose of
which is to convert the surface of the stone into a nitrate, so that
the grease cannot penetrate. This acid acts even when diluted very
energetically on the stone, and produces a fine grain.

_Hydrochloric acid_ exerts a less energetic action; it leaves the stone
smoother and does not attack it so evenly as nitric acid, but has the
same result finally.

_Sulphuric acid_ ought not to be used for etching stone. It forms
calcium sulphate on the surface of the stone, and this separates from
the stone in printing and spoils the pulls. {10}

_Phosphoric acid_ may be used for etching as well as for preparing the
stone; it exerts a very faint etching action and is seldom used for
this purpose, but principally for making corrections.

_Acetic acid_ plays a very important part in lithography. It possesses
the property, even in very dilute condition, of stopping the action of
the gum and oxalic acid, and, indeed, even that of the stronger nitric,
sulphuric, and hydrochloric acids. It finds, therefore, considerable
use in negative printing, in making corrections, etc. It converts the
stone into its original condition and makes it suitable again for
taking ink.

_Citric acid_ fulfils the same purpose, but is, however, much higher in
price.

_Oxalic acid_ is not used for etching, but only for preparation of
the stone. By rubbing the stone with a solution of oxalic acid with a
pad of cloth it takes a mirror-like surface or polish, into which the
fatty ink cannot penetrate. It is used for preparing the stone for
lithogravure, negative drawing, and negative transfer, etc.

_Tincture of galls_, or instead of this, what is simpler, gallic acid,
is used in lithography. It contains plenty of tannin, and is one of the
most efficacious means of preventing the combination of the stone or
zinc plate with fatty substances.

_Gum arabic_ or some other vegetable gum is indispensable for litho
and zincography. A 10 per cent. solution of gum is generally used. It
penetrates all the pores of the stone and the plate, and gives the same
a thin but very firm film, and prevents the ink taking on these places.
If it has become slightly acid it acts as a weak etcher, and as an
addition to nitric acid it makes the same of thicker consistence and
more easily distributable. The action of gum can be removed with acetic
or citric acid; with water alone this cannot be perfectly effected.


7.—_Etching the stone._ There are two principal etchings, the _simple
ordinary or first etching_, which obviously has the purpose of giving
the drawing the necessary stability and protecting the blank places
from taking ink, and _the deep or sharp etching_ gives for combination
printing a still greater lasting power, and for large runs keeps the
drawing clean and sharp.

The ordinary etching chiefly causes the fatty substances to assume a
new chemical condition, since in combination with the stone they form
insoluble fatty salts of lime, which represent the printing surfaces.
It has, however, also the property of cleaning the blank stone surfaces
from any adherent grease, and makes the blank parts of the stone
incapable of taking ink; also it makes the drawing clearer and more
precise.

The strength of the first etching may differ, according to the
following circumstances:—

(_a._) The stone; for hard stones stand a stronger, and soft stones a
weaker etching. {11}

(_b._) The printing image; fine drawings must at first be etched with
a weaker solution; coarser drawings, on the other hand, will stand a
fairly strong etcher.

(_c._) The material with which the print or drawing has been prepared;
very fatty developing inks and asphalt stand well even with strong
etching, whereas with lean or hard inks only a weak etching should be
used.

An etching solution which is at the limit of strength, but still
suitable for a hard stone or a very coarse drawing, would irretrievably
ruin a very fine drawing on a soft stone.

Commercial acids differ considerably in strength, and it is, therefore,
better to use a hydrometer than a measure. It is also always more
satisfactory not to use the acid by itself, but in conjunction with
gum. A solution of gum of eight to ten degrees strength is diluted with
nitric acid till it measures 10 to 12 degrees on the hydrometer. This
solution may be safely used for every case, and it is only necessary
to allow it to act longer for coarser drawings; it should be evenly
distributed over the surface of the stone with a clean soft pad. In
very hot weather it acts more energetically, and then it should be
used weaker for fine work. In any case it is advisable to let the
stone or plate stand for some hours before etching, so that the ink
may thoroughly combine. The etching of zinc plates will be more fully
described later on; in other respects the treatment is the same as for
stone.


8.—_Deep-etching process._ The idea of this is chiefly to increase the
printing form and to make the stone more resistant in printing. In
working this the principal thing is to sufficiently protect the drawing
from the action of the strong acid. This is generally done by dusting
with resin, which has a low melting point.

There are two deep-etching processes which are chiefly used, one in
which the resin is melted with a spirit flame, the other in which the
same thing is done by ether vapour.

The procedure in each case is extremely simple. In the so-called
burnt-etching process, which has been perfected by Eberle, of Vienna,
the already etched stone ready for printing is rolled up with a very
stiff printing ink, not transfer ink, and then the drawing dusted
with the finest powdered resin. The stone is then gone over with a
cotton-wool pad and plenty of talc or French chalk, and then well
dusted off with a broad camel’s hair brush in order to remove all
traces of resin from the blank stone. To melt the resin a spirit lamp
with a side flame is used. The flame is passed over the drawing, and
ought only to be allowed to act sufficiently long to make the resin
combine with the ink, which can be recognized by the drawing looking
shiny. If it has been melted too long the sharpness of the drawing is
damaged. After this the etching may be at once proceeded with, and
this is effected with a solution of gum to which 8 to 10 per cent. by
measure of 44 per cent. nitric acid has been added. For fine drawings
4 to {12} 6 per cent. of acid should be used. In using this a fairly
strong effervescence takes place, which should not frighten anyone.

In the ether or cold-melting process exactly the same procedure takes
place, only that instead of melting with an open flame this is effected
by ether vapour.

For this work a wooden stick of about 2 mm. thick is laid on two edges
of the stone. On another ruler, which should be large enough to cover
the whole of the stone, and which should be covered with flannel or
stout cloth, ether is poured; this ruler is laid on the others, so that
it forms a right angle with them, and is slowly drawn over the surface
of the stone. The ether vapour falls on to the surface of the stone and
dissolves the resin which thus forms the protective film for the deep
etching, which is done precisely as described above.

Another melting process recommended by Scamoni consists in pouring
alcohol on the stone and then setting fire to it.


9.—_Differentiation of the printing processes._ Technically we
differentiate the principal printing methods into three, according to
the method of production. _The first and oldest_ is the typographic
or letterpress printing, which is founded on the principle that every
line or every point which ought to print must stand up on the plate,
and all those places which must appear white in the print must be
sunken in. The artistic effect is obtained by tones which are formed of
individual lines or points, which are closer together or further apart,
or else print finer or deeper. In printing a forme or plate, etc., it
must be “made ready,” that is to say, the pressure in printing must be
so arranged for each part of the picture that on the lighter places
or finer places less pressure must be exerted, whilst on the deeper
tones more pressure should fall, according to their gradation. This
balancing, which is technically termed “making ready,” is effected by
cutting out the delicate and building up the strong or dark parts on
the overlay. With a proper overlay the artistic effect of the picture
can be much increased; with a faulty overlay it can be quite spoilt. In
letterpress printing the artistic element lies in the making ready.

Typographic prints are distinguished by the lines, figures, etc., being
somewhat pressed into the paper, and show raised up on the back, which
is technically termed “impression.” When this “impression” is very
plain, that is to say when the printing has gone pretty deeply into the
paper, it is advisable before reproduction to remove this by strong
pressure.

The second method of printing is exactly the opposite of the first,
and is founded on the principle of printing from intaglio. The lines
and points which should print are cut mechanically (by engraving or
piercing) or chemically (by etching) into the stone. The etched or
engraved intaglio plate represents a negative, or a reversed wood-cut,
only with the difference that the lines do not {13} lay in the same
plane. In order to obtain an impression the ink is pressed into the
cut-out parts, and is wiped off from the surface of the plate. By
stronger or weaker wiping the print receives a stronger or weaker local
tone, which is of great advantage from an artistic point of view, but
which forms no small obstacle to the reproduction.

The impression is represented in relief on the paper. According to the
depth of the lines they take more or less ink, and appear therefore
raised up in the impression according to the amount of their depth in
the plate. Reproduction photography has to reckon on this disadvantage,
for with a side illumination the raised up lines cast shadows, and a
correct negative does not follow.

By the third method, lithography, of which we have already spoken,
the impression lies generally flat on the paper like a drawing, if
a very strong deep etching was not used, in which case it is also
slightly raised. In printing from the graver or from stone etching a
faint relief is generally noticeable, which is never so high as with
copperplate printing, and which is no important obstacle to making a
photographic negative.

{15}




CHAPTER I.


1. GENERAL NOTES ON PHOTO-LITHOGRAPHY.

By photo-lithography we generally understand that process by which
it is possible to prepare a printing plate or a stone by the aid of
photography from any original, whether it be a drawing, a print, or an
oil painting, either of the same size or smaller or larger than the
original, which can be reproduced in the lithographic press.

The main characteristic of this process is that either the original
from which the reproduction is to be made must be prepared in distinct
lines, strokes or points, or that any half-tone which may be present in
the photographic negative must be broken up on the stone or plate into
lines or points.

The basis for the preparation of a photo-litho is as a rule a
photographic negative on glass or gelatine, which, as the word negative
implies, when examined by transmitted light, must have all its tones
reversed, that is to say, the drawing or the lines, strokes or points
which must in the print be black, must look transparent, whilst the
other part of the negative which forms the groundwork must be covered
or opaque.

If every photo-lithographic process was to be described in detail
there would be a great many, but actually they may all be classified
according to two principal methods:—

(_a._) One, in which the stone or plate is itself coated with the light
sensitive substance and exposed under a reversed negative, so that a
reversed image is formed on the stone or plate, which in printing comes
in the right position, and

(_b._) The other, in which paper or a very thin zinc plate, provided
with a light sensitive film, is exposed under an ordinary, that is not
reversed negative, and thus is rendered capable of receiving fatty ink,
and is then transferred to the stone or plate by transfer.

Of the many processes which, though differing in detail, may, looking
to the final result, be assigned to one or other of the above-mentioned
principles, there are two which have been especially tested in
practice, namely, for _the direct transfer_, as we will call it, that
process which is based on the light sensitiveness of asphalt or of an
organic substance in combination with a {16} chromium salt; and for
_the indirect transfer_, that process which is founded on the light
sensitive chromium salt in combination with gelatine, or briefly on
the light sensitiveness of chromated gelatine. All other more or less
complicated methods have disappeared from technical practice and have
only the honour of being scientifically interesting and theoretically
correct, but for various reasons are not practically valuable.

It is indeed obvious that a discovery so important and useful to one
of the principal departments of the graphic arts as lithography is,
and which may be called even more essentially capable of variation
and multiplication, and perhaps in its way also more artistic, should
call forth an earnest movement on behalf of the technical experts,
principally with the endeavour for simpler forms and extension of its
powers of work. This, indeed, has not always been attained, and these
attempts will therefore only be taken into consideration in this book
as may appear necessary, and all others will be passed over in silence.

The methods used by some experimentalists for direct transfer, which
consist in coating the stone with a solution of gelatine, albumen,
or gum made light sensitive with a chromium salt, and after exposure
under a positive or negative, obtaining a printing plate, were in
execution complicated and troublesome, but in results fairly safe and
satisfactory, so that they are now more and more used in practice.

Iron and silver salts have been proved as not very suitable for
photo-lithography, and at the present time for direct transfer asphalt
is most generally used, and latterly also organic substances rendered
light sensitive by a chromium salt; for indirect transfer chromium
salts in combination with gelatine, or chromated gelatine.

_Asphalt_ exposed to the action of light undergoes a chemical change
which consists in its becoming less soluble in its original solvents.
This was known to Nicephore Niépce, one of the discoverers of
photography, whose endeavours to produce images by the action of light
were actually based upon this very property of asphalt. He used for
this purpose metal plates which were converted by a species of etching
into printing plates.

In the year 1852, the well-known Parisian lithographer Lemercier, in
partnership with Lerebours, obtained a patent in France for a process
by which they were in a position to obtain images on stone by the
exposure of asphalt, and thus reproduce the same by printing in the
ordinary way. They coated a lithographic stone with ethereal solution
of asphalt, exposed it under a negative and developed it with ether;
there remained behind then the parts which had been rendered insoluble
by light and formed a positive asphalt image on the stone, the outlines
of which had the property of taking up greasy ink and with suitable
preparation of giving an impression on paper. Such a stone was etched
in the ordinary way with acid and gum, and then it was possible to make
as many {17} pulls from it as was desired in litho ink. We have here a
practical photo-lithographic asphalt process, as it is at the present
time practised with various modifications, and which gave satisfactory
results.

Other resins besides asphalt may also be rendered sensitive to light,
and it is well-known that they also may be used with as good results as
asphalt for photo-lithography.

That the good qualities of asphalt were even earlier recognized is
proved by the fact that Negré, before the discovery of zinc etching,
exposed a copper-plate coated with asphalt solution under a negative,
washed out the places not affected by light, electroplated these blank
places in a gold bath, then cleaned the plate and deep etched it with
acid. He obtained in this way an intaglio printing plate similar to an
etching.

By using a positive with this process a relief or typographic plate
may be obtained, both of which processes are known as “gold etching,”
and were practised in the beginning of the ’50’s in the K. K. Hof- und
Staatsdruckerei.

The asphalt which is used for photo-lithographic purposes must possess
certain qualities, of which the most important is as high a light
sensitiveness as possible. With ordinary asphalt success will not be
attained, since it is only slightly sensitive to light; the so-called
Syrian asphalt is therefore generally used, which after having been
prepared is dissolved in chloroform and then benzole and oil of
lavender are added.

Professor Husnik prepares an asphalt from which all constituents not
sensitive to light have been extracted. Herr Valenta produces his
sulphurized asphalt. Both possess a far higher light sensitiveness
than ordinary Syrian asphalt, and are specially suitable for
photo-lithography.

The second, and considerably more extensively used method for
photo-lithography—a transfer process—is based on the light sensitive
property of the chromate salts in combination with gelatine, or
albumen, or gum.

That the bichromate salts possessed light sensitive properties, and
could be used for photo-lithography, Mungo Ponton discovered in 1839.
He printed on an ordinary paper, which had been rendered sensitive to
light in a solution of potassium bichromate, drawings and silhouettes,
and obtained after fixing, which was effected by merely washing in pure
water, brown images on a white ground.

Later Talbot found that the chromate salts in combination with
organic substances under the action of light altered the property of
the latter, and particularly that exposed chromated gelatine became
insoluble in hot water. Poitevin used this discovery for carbon or
pigment printing, and had produced in 1855 various pictures with this
process.

Poitevin discovered, further, that exposed chromated gelatine {18}
would not swell up in cold water and took up greasy ink, and therefore
after exposure under a photographic negative a picture could be
obtained exactly inversely corresponding to the tones of the negative;
and that these places affected by light could be inked-up and printed
from, or could be transferred to a zinc or stone plate, and from this
pulls could be prepared. By this discovery photo-lithography and
collotype were actually discovered.

Led on by his success, Poitevin used later, instead of gelatine,
albumen and gum arabic, and prepared with these photo-lithographic
prints, which were transferred to stone.

If a solution of gelatine is mixed with a solution of bichromate of
potash, and a sheet of paper coated with this mixture and exposed,
or if the paper is first coated with gelatine and then bathed in a
solution of bichromate of potash, various chemical changes take place
as the result of the action of light on the gelatine film, which we
will now consider.

As has already been mentioned, glue or gelatine is insoluble, and
only swells up in cold water. In warm water, however, the gelatinous
substance dissolves completely, and sets on cooling to a jelly. If a
suitable sheet of paper is coated with the warm gelatine solution,
either by floating or pouring it over it, and it be allowed to set, and
if this film is now made light sensitive in a solution of potassium
bichromate and dried in the dark, we shall have a photo-lithographic
paper which, according to the greater or less quantity of the chromium
salt used, has a more or less intense yellow colour. If the paper thus
prepared is exposed to light under a negative, or in another way if
some places before exposure are protected by black ink or strips of
paper, the places affected by light become dark coloured and brown,
and at the same time they have lost their power of swelling up in cold
water. The whole surface of the paper, that is to say the exposed and
unexposed films before being laid in water, are flat or in one plane;
if, however, the print is laid in cold water the exposed parts are not
affected by the water, that is to say they have lost the property of
swelling and remain in their original plane. The unexposed parts swell
up and appear raised up on the print, and thus make the drawing sunken
in.

The exposed places have, however, now received the property of taking
up and holding greasy ink, whilst the unexposed have taken up water and
repel greasy printing ink.

If the paper be exposed under a negative the drawing appears sunken in
after development with water; the other parts, which must in printing
appear white, are raised up; by exposure under a positive the reverse
is the case.

If these prints are in any way, either by rolling up or brushing over,
given a coating of greasy ink, the ink only adheres to the exposed
places and a print in greasy ink is obtained, which, like any other
greasy impression, can be transferred to a stone or a metal {19}
plate, which can be printed from direct, or the transfer may be
made on to a metal plate for relief etching, that is to say for the
preparation of a typographic block.

In Poitevin’s process the stone itself was coated with a light
sensitive chromated film, and exposed under a reversed negative. After
developing and careful preliminary preparation of the stone the ink
only adheres then to the places affected by light.

This is also the case if the stone is coated with light sensitive
asphalt, and the same printed on direct. After exposure the parts
not affected by light can be washed off with turpentine, benzine, or
linseed oil, so that the stone is laid bare; the places, the parts of
the drawing affected by light, however, are not dissolved. If the stone
is now prepared with the solution of gum as has already been described,
and then rolled up with an ink roller, these places will take the ink,
and by etching, etc., the stone may be so prepared that the same may be
printed from like any drawing or engraving.

By photo-lithography only line or grained drawings can be reproduced,
and half-tones, as is possible with collotype and photogravure, cannot
be obtained.

Now, with the aid of autotypic transfers and the asphalt process
on grained stones, we have a perfectly satisfactory method of
reproducing in an excellent manner half-tone drawings by the aid of
photo-lithography.

Photo-lithography in all its various branches of application is at
the present time so perfected, and rests on so comparatively a simple
principle, that a technical printer, with very little practice,
experience, and observation of the formulæ given, can attain in very
short time absolutely good results. At the same time it must be said
that frequently very great difficulties have to be contended with;
especially as regards the quality of the materials and negatives great
care must be used.


2. SUBJECTS WHICH CAN BE REPRODUCED BY PHOTO-LITHOGRAPHY.

The next question which arises is, “What can be reproduced or
multiplied by means of photo-lithography?”

The answer is, “According to the existing state of the technique of
photography and the perfection of the transfer process, everything.”
Any line or wash drawing, any oil painting or other plastic object,
any photograph of living creatures or lifeless objects—briefly, any
photograph can, under certain conditions, be transferred to stone
or a metal plate, and from this any number of impressions in greasy
ink be obtained. Before the discovery of the method of breaking up
half-tones into points or dots, only line drawings could be reproduced
by photo-lithography. Since, however, it has been possible to break up
half-tone into line or points or grain, nothing stands in the way of
reproducing by this {20} method any kind of original. This breaking up
of the half-tone into a regular or irregular grain can be effected by
means of a crossed line screen in making the negative, as in autotypic,
or half-tone, block-making, or independently of the making of the
negative, as in the asphalt process of Orell, Füssli and Co., and in
Bartös’ process and various other methods.

The undesirable half-tone must, however, always be broken up in
some way into the requisite points or lines, as it is one of the
characteristics of lithography that it is only possible to print from
distinct figures on the stone. Lithography and letterpress printing
produce impressions of sharply-defined lines or points, each of which
must form a distinct whole. Any tone which is lighter or not absolutely
black must be formed by lines or points standing in close proximity to
one another. The tonality must be formed by stronger or weaker lines
or points, by black and white spaces, or by more or less close line
and point patterns. An absolutely closed tone, as in collotype or
photogravure, is not attainable with lithography, and although numerous
experiments have not been wanting to reach this end, the same have
hitherto been without success.

The half-tones are broken up and separated into solid printable points:—

(_a._) By the autotypic transfer, which is effected by placing in front
of the sensitive plate when making the exposure the above-mentioned
crossed-line screen.

(_b._) By the so-called asphalt process, by means of preliminary
graining of the stone before coating with asphalt and printing.

(_c._) By means of the production of a grain on chromated gelatine.

(_d._) By the use of a sand blast, which is the chief point of Bartös’
process.

(_e._) By transfer of a close grating or network on to a polished
stone, which forms the basis of the litho-heliogravure process of
General-Director Chas. Eckstein, which is included in photo-lithography.

All these methods have for their purpose the breaking up of the light
tones into regular or irregular but separate points. There are other
methods besides those mentioned above which have the same purpose.

We generally distinguish two kinds of reproduction:—

(_a._) Those from line drawings, in which a negative is made without
the interposition of a cross-lined screen, and for which no other means
is used for the production of a grain, and

(_b._) Those from wash-drawings, paintings, photographs from nature,
etc., in which reproductions the half-tones are either broken up into
lines or points by the use of the screen when making the negative, or
by any of the other above-mentioned means after making the negative.

{21}


(A.) LINE DRAWINGS.

By the first method the drawing must be prepared according to certain
formula if a good negative is to be obtained which shall not require
much after work and disadvantages for photo-lithography. A poor
original may cause a partial or complete failure of the work, or
at least cause much cost and waste of time; therefore it appears
advisable to pay the necessary attention to the original which is to be
reproduced.

What a line drawing must possess which should be reproduced well by
photo-lithography in order to give a good transfer on to stone we will
now point out.

Before all things should be noted that the paper must be pure white
and smooth, yet not strongly reflective and not too weak. Smooth white
cards of medium thickness are the best to use. Since all lines of the
drawing appear in the impression of the same colour, there is not only
no purpose, but it may even be very disadvantageous to the reproduction
when the draughtsman, in order to increase the artistic effect of his
work, or to produce good perspective, etc., draws fine lines or other
points in a lighter colour. The striving of the artist for effect,
perspective, etc., so far as this is attained by lines or parts of a
lighter colour, has for this process of reproduction no advantage, but,
indeed, the disadvantage that by this the subsequent manipulations are
rendered more difficult, the whole work will turn out more costly and
finally less satisfactory.

Although from the present position of photography drawings in any
desired colour can be reproduced, yet it is most advantageous if the
originals for photo-lithographic reproduction are drawn with fine black
matt ink on smooth white papers, and the principal point to which
attention should be directed is that all lines, even the finest, should
be a good black, and should be kept of the same strength of colour as
the other parts of the drawing. The thick lines must be quite filled
up like the shadow lines of a strong letter. Shading must be obtained
by strong, fine running lines quite separate from one another. In this
the single black lines must not be too strong, and the white spaces
in between must not be too narrow, or otherwise when reduced in size
the white interstices will disappear and will finally form a solid
tone. The laying on of a tone or wash is not permissible, as even a
light tone will appear in the reproduction as a black spot. It is not
permissible also to draw on the same original with inks of different
blackness or consistency, and even if a coloured ink be used the whole
original must be prepared with one colour (red, dark blue, green, or
brown), and that as intense as possible. When we start from the only
true standpoint, that every reproduction should be a reflex of the
original as true as possible, artistic effects have from this point
of view no purpose, since the printer in printing with {22} one ink
is not in a position to give grey lines as well as black, but can
only give the appearance of everything in one colour only. He is,
however, able to give with the strongest line the finest with their
own characteristics, and can, therefore, in this direction attain the
tonality of the original.

It is obviously, therefore, the artist’s duty to draw in one colour,
and since for photographic reproduction black is the best, that is to
say Chinese ink, he will do well to completely lay on one side all
other artistic materials or effects. At the same time it should be
noted that originals drawn in any other colour can be reproduced by
photo-lithography, but if the drawing is to serve no other purpose than
for reproduction it is best to prepare it in black.

A further important requirement is that the drawing be sharply and
cleanly worked, and since the reproduction of a ragged or broken line
cannot make a full smooth beautifully running line, they will appear
in the reproduction in the same defective way, and then require at
least tedious retouching or make the printing of the subject actually
impossible. If it is necessary to cross the lines in the shadows this
must be done with great care. The points of crossing must be clean and
sharp, and the ink must not run. Too close or too frequent crossing
of the lines should be avoided, and would produce a bad and different
effect in the reproduction. Smudges or wrinkles in the original appear
in the reproduction more intense and more vigorous, and therefore it
must not be forgotten to carefully avoid these, also any tracing lines
must be erased, without, however, damaging the ink lines or rubbing up
of the paper.

Pencil and chalk drawings, assuming that they are cleanly executed,
can be well reproduced by photo-lithography, only they ought not to
be smudged or inked. Erasure marks on pencil drawings appear in the
reproduction as smudgy spots.

Drawings of architecture for illustration or other purposes, after
consideration of these remarks, can be well transferred without much
trouble by photo-lithography on to stone or zinc.

In drawings of maps, plans, etc., there are still some rules to be
observed besides the above. Boundary lines or mountain ranges with fine
hatching, waterlines for large rivers, seas or lakes, as well as the
introduction of figures, are better left out of the drawing, and can be
afterwards drawn on the stone; they will then be cleaner and sharper.
If all these details, however, must be introduced into the original
drawing, they should be executed in a pale blue colour, which will not
appear in the ordinary negative.

For plans with large letters it is better not to draw the latter, which
are frequently a lot of trouble, but to employ the simpler plan of
getting the titles, writing, legends, explanations, etc., printed by
a book printer on paper of the same colour as the original, and stick
them on the latter. The same method may be {23} adopted when preparing
railway, postal, and telegraphic charts or maps with a lot of names or
other titles, etc. The network of lines may be drawn with litho ink as
suggested above, but the names of the stations, etc., can be printed
with letterpress and stuck on in the proper places. Working in this way
not only will much labour be saved, but at the same time sharper and
more correct titles be obtained on the reproduction.

Any necessary instructions for carrying out the drawing should never be
made on the paper with red pencil, but either with pale grey or pale
blue. For this paper rubbed with indigo or graphite can be used or a
scratched gelatine proof which has been rubbed with finely powdered
milori blue.

With commercial drawings it frequently happens that ornaments are
repeated. It is not necessary for the designer to draw all the
ornamentation, which may frequently be very complicated, if it runs
over the whole of the design. It is quite sufficient, according to the
size or the number of times that the ornament occurs, for the artist to
draw it twice or three times, or sometimes ten to fifteen times; the
lithographer will duplicate it by transfer. This also applies if there
is a border, or if there are any corner or centre pieces repeatedly
used. It is quite sufficient to draw one-fourth of the frame or border,
or with very complicated designs a complete corner, and to give the
printer a rough sketch of the complete border. He will make the
necessary impression on transfer paper by photo-litho transfer on the
stone; he will also reverse the drawing from right to left, join up the
different parts, and thus construct the whole border. This applies also
to the corner and centre piece.


(B.) DRAWINGS ON BLUE PRINTS.

As a substitute for a proof cyanotype or blue prints may be used for
preparing drawings for photo-lithography and other graphic arts. When
a photo-lithograph like a pen and ink drawing is to be prepared from
a coloured picture, or from a sepia or Indian ink wash drawing of a
plastic object or a photograph from nature, or from an object not
suitable for photographic reproduction an autotypic transfer is to
be prepared, a proof of the desired object must be first prepared,
and then from this the drawing is to be made. It is obvious that the
proofs of the first-named can only be made in the original size, which
under some circumstances may not be just what is required, assuming
that the original can be used in this way. In all cases this will be
inconvenient and tedious, and possibly from the nature of the drawing
many proofs be lost. The end will be attained far more quickly and
safely if a negative is made of the original, either of the same size
or enlarged according as may be desired. The negative thus obtained is
used to make a ferro-prussiate print. {24} For this we use a good firm
drawing paper, which is sensitized in the following mixture:—

 Solution A.
     Potassium ferridcyanide      8 parts.
     Water                      150 parts.

 Solution B.
     Ammonio-citrate of iron     10 parts.
     Water                      100 parts.

When dissolved each solution is filtered and mixed in the dark room
immediately before use in equal parts. The solution thus formed is
sensitive to light and is spread on a well-sized drawing paper as
evenly as possible with a broad brush, equalized with a distributing
brush, and then dried in the dark room.

The coated side of the paper appears yellowish. It is then printed as
usual until the deepest parts look grey, as the prints look weaker
after developing. The prints are developed by floating them face
downwards on a dish of pure water not too cold, and then washed till
the drawing appears quite white on a blue ground. The washing must be
thoroughly done or else the prints turn blue afterwards when exposed to
light. These prints contain all the finest details, even in the deepest
shadows, plainly visible, and will now be the most, perfect and most
convenient proofs for the artist. The tracing or drawing is now done
with good black dull surface ink as already suggested. When the drawing
is done it is allowed to dry thoroughly, which will be in from two to
three hours. The following solution should be prepared:—

 Oxalic acid      1 part
 Water           10 part

which should be poured into a flat dish and the drawing allowed to lie
in it for about thirty minutes. It is then again well washed and then
immersed for fifteen minutes in a bath of

 Hydrochloric acid      1 part
 Water                 20 part

The blue colour will now have disappeared, and the ink drawing will
appear pure black on the white paper. It should be now hung up and
dried in the ordinary way. This drawing prepared in wash or line with
ink now forms the original for a further photographic negative, which
is made in the correct size of the reproduction with or without the
intervention of the crossed screen according to the character of the
drawing. With the negative thus obtained a photo-litho on stone or
zinc, or a typographic copper or collotype plate, or a photograph on
wood for xylography may be prepared.

The use of this process appears specially important for those cases in
which an ordinary photographic negative is not sufficient, {25} for
example where a printing plate cannot be prepared from the negative.
It ought also to be useful when the light could not be controlled
in making the negative, and thus incorrect effects appear in the
reproduction, which often occurs in negatives from nature and with
polished plastic metal objects. The enlargements from the original are
then used because the details can be better seen, and the artistic
character can be more easily seen. The fineness of the drawing must
obviously be in proportion to the after reproduction, while tones may
be partly or entirely lost.


(C.) DRAWINGS ON PREPARED PAPERS.

For photo-litho transfer without the use of a screen there are some
commercial papers, toned, grain, net or pyramid grained papers which
may be used with excellent results.

On these papers, according to their preparation, various excellent
results can be obtained, which possess high claims as illustrations.

A smooth white scraper board made by Angerer and Göschl of Vienna,
which has a very even film of chalk, and which takes the lines clean
and vigorously, is especially suitable for pen and ink work. On this
paper plucky drawings like woodcuts can be executed. The perfect whites
of the paper, combined with the vigorous beautiful black, facilitate
reproduction with excellent results and without much trouble.

An ordinary writing pen and ordinary Chinese ink are used for drawing.
The ink gives sufficiently black and matt lines.

The deepest parts are covered with ink, and the desired shading or
stippling put in with the toothed scraper or engraving tool. The
shading off of the shadows may also be worked up with the toothed
scraper, and thus very delicate shading be obtained.

Two more very useful papers by the same firm are known as scraper
boards with printed lines or points, and white scraper boards with
simple or double lines stamped on to it. These papers are also coated
with a chalk film.

  [Illustration: Fig. 1.]

With these papers the printed lines or dots serve as half-tones for
the artist, and by scraping with smooth or toothed scraper knives very
many effects can be obtained. Lead pencil, chalk or litho ink can be
used for drawing. For laying on, ordinary ink with a small addition of
soap may be used, and new tone effects {26} may also be produced with
a half dry Chinese ink brush, but for any drawing for line reproduction
washing with paler or darker inks is excluded. By scraping with the
smooth scraper, points are formed in place of the lines, which by
further scraping disappear entirely into white, by which means the
transit into the highest lights is effected. If a black surface is
scraped with the smooth knife a line tone is produced in the opposite
direction to the printed one. By the aid of the toothed scraper lines
in any desired direction can be obtained. When the printed tone is only
desired in parts in the picture, the other parts can be covered up
with white paper. The paper is only stuck down by the edges with mouth
glue; if it were stuck down all over with gum or starch it would be
distorted. On the white paper stuck on, drawing may be done with the
pen, and thus new effects again be obtained, as thus in a manner pen
and wash drawing are combined.

The white scraper boards without printed lines or dots are either
impressed with a single line or with lines crossed at right angles.

On this paper pen and ink drawings combined with grained tones may be
done. The outlines and everything which is to be treated like a pen
drawing may be done with a hard pen or a marten brush. Bright tones
are so worked with the brush that smooth surfaces are not formed, but
dotted darker or lighter tones. Those parts which have been laid on
quite black can be brightened up afterwards with the smooth or toothed
scraper knife or the needle, and thus many gradations obtained. Instead
of the litho writing ink pastell or very black good litho chalk may be
used for drawing. Obviously this paper also ought not to be washed or
smeared.

The pyramidal grain paper prepared by Schäuffelen of Heilbronn is also
very suitable for drawings for photo-lithographic reproduction. The
paper is coated with a chalk film of blinding whiteness, and is stamped
with a regular grain of truncated pyramids, and is produced in three
numbers. Grain No. 1 contains 2,500 regular projections per square
centimetre; grain No. 2 contains 1,500; and grain No. 3, 750 pyramids.

This paper is drawn on with litho chalk or black pastell crayons.
The deepest shadows are laid on quite black, and light effects are
introduced with the scraper or engraving needle as with the above
described papers. The same rules apply to the other parts of the
drawing.

For drawing in general or the use of effects in drawing it should
be noted that with all these papers the drawing may be somewhat
overdone, and this is necessary in order to obtain the corresponding
vigorous action in the reproduction. The printing ink is, as a rule,
never such a deep black as the drawing ink, nor is the paper which is
used for printing ever so white as the lines of the toned paper. The
contrasts would, therefore, in printing become too {27} little, and
flat unsatisfactory pictures would be obtained. With these drawings,
therefore, the two opposites, “black and white,” may be used to the
extreme, even if the drawing is not satisfactory to the artistic eye.

For making the drawing red paper ought not to be used, as when
photographed red appears dark. Then blue proof paper, or paper rubbed
with lead pencil, should be used.

A drawing for photographic reproduction ought never to be rolled, and
still less be folded; if it is to be sent away it should be packed flat.


(D.) REPRODUCTION OF PRINTS.

It is frequently required to make photo-lithographs of old prints.
As already mentioned in the introduction, we distinguish three
different methods of printing, of which the two first, typography
and lithography, are confined to the rendering of well-defined lines
or points, whilst copper-plate printing can to a certain extent
reproduce lines and tones. As regards the reproduction of the first
two, so far as their fundamental character goes, no insuperable
difficulties present themselves, when they correspond at least to
the general requirements of a drawing. Since a reproduction, with
exceptions, can never be better—obviously without very complicated
retouching—but always somewhat inferior to the original, the appearance
of the original will always be some guide as to the quality of the
reproduction that can be produced.

If, however, prints are prepared specially for this purpose, the
following points should be observed:—

1. For printing a matt surface a so-called pure white chromo paper
should be used.

2. The ink should be black and of good body, the impression clean and
sharp, every line exact and not in the least fuzzy.

The expert lithographer will easily prepare his impression. Assuming
that he has a good original stone, he will more easily make good and
correct prints from the engraving from the chalk, pen or other drawing
than the typographer. The latter has to give his impressions the
correct finish by means of overlays, without the correct making and use
of which no good picture, whether it be characters or a drawing, can
be obtained actually on a typographic press. The reader is referred
to my article in Professor Eder’s “Jahrbuch für Photographie und
Reproductionsverfahren” for 1891, where I have treated of this at
length. Prints produced by the third method, copper-plate printing,
give far greater difficulties to the photo-mechanical worker. Every
pull from the engraved plate—etching scraper drawing and photogravure
excepted—possesses a tone on its surface, which is, moreover, very
unequal, and although increasing its artistic qualities, offers,
however, considerable difficulties for reproduction. This can {28}
only be avoided by very troublesome retouching, which is frequently
prejudicial to the beauty of the picture.

If pulls are specially prepared for reproduction the copper-plate
printer must very carefully polish his plate and print without a tone,
but still this must not be done so that the plate is too strongly
polished that the depths lose their vigour; this would give an
absolutely incorrect picture as regards gradation of tone.

Etchings can, as a rule, only be reproduced with the aid of a
cross-grained screen, and the same applies to photogravures, although
the latter will seldom be required.

All tone or painted originals, such as wash or sepia drawings,
photographs from nature, collotypes, photogravures, water-colours
and oil-colours can only be reproduced by photo-lithography by the
interposition of a screen when making the negative, or by a process
in which the breaking of the tone is effected independently of the
photographic negative, and which will be described later on.

With old photographs which have faded it is as well to increase the
lights and shadows by painting.


(E.) SIZE OF THE REPRODUCTION.

A question frequently asked is, “Of what size should a drawing be made
in order to obtain a good photographic reproduction?” This question
cannot be precisely answered, for a good deal depends upon the object
itself, and on the kind of drawing.

It may be generally said, however, particularly as regards pen and ink
drawings on smooth paper, that they should never be smaller, only very
rarely of the same size; they should be drawn one-third or one-half
larger generally. The artist can execute fine details more easily and
precisely on a large drawing than on a small one.

The enlarged reproduction gives any faults or mistakes which may happen
to be in the drawing in proportionately larger size quite independent
of the fact that an enlarged reproduction is always somewhat rough and
ordinary. Reproduction in the same size reproduces the faults the same
size as they exist in the drawing; the reduction, however, also reduces
the failings of the drawing if it cannot also absolutely remedy the
same. The reduced copy has always something finer and more delicate.
The degree of reduction must be kept in mind, and the drawing be done
with this in view.

If a drawing is executed very finely and full of detail, and, besides
that, contains very small lines of drawing or titles, they do not
gain in reduction, but the opposite; they lose, as much that in the
drawing appears plain and distinguishable becomes by strong reduction
indistinct and unrecognizable, or appears to the eye as a tone. {29}

Individual cases, in which for specimen purposes or to show how far
reduction can go, many times linear, five, six, to ten times, cannot be
taken into consideration, although the effect is usually well attained.

It should also be observed that the drawing must be considered not
only as regards its size, but also the strength of the lines and
tones generally for reduction; this specially applies as regards the
tones. By reduction the tone gradations are compressed, the picture
becomes poorer in tones, and although, theoretically considered, light
and shadow, that is to say black and white, are actually distributed
in the same ratio as in the original, yet the reduced image appears
proportionately darker and loses in artistic effect.

Great reductions will, however, be useful when for some special purpose
such as the exact reproduction of geometrical figures or surface
ornaments are required, as for instance in printing designs for
cheques, bank notes, etc. In such cases the drawings should be made as
large as is necessary for the most exact and easiest carrying out of
the figures, as in this way the precision of the drawing is better kept
by reduction. In such cases, assuming that the ornaments are clear and
open without shading, the reduction may be carried beyond one-tenth
linear.

This kind of reproduction should present no difficulties either to the
reproduction or printing.

It is quite different, however, with drawings on scraper boards or
grained paper. If it is kept in mind that with too great reduction the
gradations of tone of the print will be destroyed, and that in the same
degree the difficulties of printing will be increased, care should
be taken that reduction is not carried too far. When it is further
considered that in a reproduction with 2,000 to 3,000 points to the
square centimetre the individual points disappear to the unaided eye,
and the different thick layers of points appear as closed tones, the
limit of reduction will soon be found.

If we reckon according to this view, we can assume that those kinds of
paper with coarse grain should be reduced at the most one-third, those
with a finer grain a sixth, at the most a fourth, in order to obtain
good printing plates which will give large editions. In this obviously
will a good deal depend on the character and more or less rich in
detail execution of the drawing. Still there are photo-lithographic
processes such as the asphalt process of Orell Füssli & Co., which
contains about 15,000 points, and Bartös’ process, which contains
11,000 points to the square centimetre; still for reproduction in
large quantities these processes offer many difficulties, and cannot
therefore really be taken into account when considering this.

{30}




CHAPTER II.

THE PHOTOGRAPHIC PROCESS.


1. THE STUDIO.

The arrangement of the reproduction studio is essentially different
to that for ordinary portrait work. The general points of such
arrangements are described in detail in the handbooks of Drs. Eder and
Vogel, and these I may therefore omit so far as nothing novel is to be
observed.

We distinguish now between daylight and artificial light studios;
further, those in which a camera is used for making the negative and
those in which a dark-room itself is the camera. The first will, of
course, be used where other things besides reproductions have to be
made; the arrangement without a camera presents many advantages for
reproduction work only. In the arrangement with artificial light the
illumination of the object to be taken is effected as a rule with a
source of light which can approximately replace daylight, and which
also remains as constant as possible, and the electric light is at
present the best. Although other sources of light are sometimes
used, the electric light in the form of the arc light for continuous
practical use has the advantage. For copying oil paintings daylight is
to be preferred under all conditions, and for this the best arrangement
is the revolving studio.[1]

  [1] See Eder’s “Jahrbuch für Photographie,” 1893, p. 231.

The description of a modern studio with electric light as used in the
K.u.K. Militar-geographischen Institut in Vienna, and from which the
studio of the K.K. Hof- und Staatsdruckerei was copied, is given here.
This studio lies seven metres below the level of the street on the
south front of the building, and is shown in Fig. 2.

The preparation and dark rooms are illuminated with white, yellow, and
red light by means of two 50-c.p. incandescent electric lamps for each
colour, and besides this are provided with window screens of glass of
the same colours for daylight.

The windows open into an area 50 cm. wide which runs round the
building. The lighting is so arranged here that besides the ordinary
collodion plates, very sensitive gelatine plates can be worked. The
room C, where the original is placed, is fitted up {31} with four
Franzen arc lamps of 3,000 c.p. each for illuminating the original,
and the lamps are so arranged that the light falls centrally on the
original. The four lamps are fastened by ball

  [Illustration: Fig. 2.

  A is the room for the preparation of the plates, for the wet
  collodion plates, and the silver bath.

  B the developing room.

  C is the room in which the original is placed, where is found a
  support for the original TT′, as is shown in Figs. 3 and 4.

  D is the dark-room with the focussing table EE′ (Figs. 2 and 3), and
  is separated from C by a wall of 15 cm. thickness. In this wall is
  found the photographic lens in a metal flange built into a stout iron
  box.

  F is the washing and polishing room for the glass plates.]

and socket arms to an iron frame which rests on rollers; they can be
raised or lowered on the frame, and for taking small objects can be
pushed closer together. The arms are fastened to the round pillars of
the frame, being provided with a screw grip. The lamps can be placed as
close as 0·5 m. to the original. As a rule, however, they are worked at
a distance of one metre, as then the intensity of the light is about
equal to diffused daylight. The axes of the carbons in the lamps are
so arranged that the glowing crater formed in the positive pole is
turned to the original, by which means the illumination is intensified.
The positive carbons have a diameter of 20 mm., the negative carbons
8 mm. The lamps stand in pairs one above the other at LL′. In the two
upper lamps the positive carbon is at the top and the negative carbon
below it, so that the light is equally distributed over the whole of
the subject. With this arrangement of the lamps all reflections are
avoided, and neither the grain of rough drawing paper, the relief of
an engraving, nor the edges of pieces stuck on are felt. The current
is produced by a dynamo in the house; it enters into the place at N,
whence it is divided into two circuits of 20 ampères, in which are two
switches, an ammeter and a rheostat, and the two lamps on either side.

The wall in which the objective O (Figs. 3 and 4) is placed, as also
the brick socle _aa_ and _ee_ (Fig. 2), on which the support for

{32}

  [Illustration: Fig. 3.]

{33}

  [Illustration: Fig. 4.]

{34}

the original and the focussing screen rest, run on rails, and are
absolutely isolated from the brickwork of the building in order to
avoid any possible vibrations.

The stand for the original TT′ is provided with screw fittings, cams
and wheels, which make it possible to raise the original, to lower
it, to move from right to left, and _vice-versâ_, vertically and
horizontally, so as to place its centre axial with the optical axis of
the lens, as well as parallel to the focussing screen in the dark room.
The whole of the mechanism lies at the back of the stand, so that there
is absolutely nothing in front of the original.

The focussing table EE′ is constructed in a similar manner to the stand
for the original, and is movable in every direction in the same way. It
carries in front two wood clips, in which the board with the original
is placed. The table for the original, like the focussing table, is
constructed on rollers, which run on the already-mentioned rails. In
order to be able to fix these as soon as a sharp focus is obtained a
brake is fitted. The placing of the original table at the distance from
the lens is accommodated according to the size in which it is to be
reproduced, and has already been estimated. There remains, therefore,
only to trouble about the fine focussing, which is very quickly
effected.

For taking line or wash drawings and for enlargements up to 80 × 80 cm.
a Steinheil wide-angle aplanat is used, which gives no distortion. The
duration of exposure is with such subjects from eight to ten minutes.
For smaller subjects, and principally for photographs on wood, an
orthoscope by Voightländer is used, and the exposure varies from four
to six minutes.

A Zeiss anastigmat is used for making autotypes. Duration of exposure
from three to five minutes. Coloured objects, oil paintings, etc., are
taken in the daylight studio. They are printed in the daytime in the
open air, and in bad weather or under pressing circumstances in the
night by the electric light.


2. THE GENERAL QUALITIES OF NEGATIVES FOR PHOTO-LITHOGRAPHY.

The negative for photo-lithographic work, for whatever method it may
be used, must before all things possess two principal qualities; when
looked through it should be as clear and as clean as possible, on
the other hand the ground as well covered as possible. The deposit
must not be of a black colour; from a well-drawn original absolutely
satisfactory negatives can be prepared without the black colour. When
a drawing is reduced which contains grey lines, dots, and points,
as well as full black ones, toned lines will be visible as well as
the transparent; with careful treatment, the negative may be so far
corrected that it may be used. If this is not effected, or is not
possible, the retouching on the stone will be somewhat troublesome.
The toned lines print later than the transparent; these will therefore
be overprinted {35} when the former have scarcely reached the correct
degree of printing. The choice is then only left either to weaken the
lines which are too strong or to draw afterwards the faint or not
printed lines.

If the ground is not sufficiently opaque it will print through. This
can be remedied by intensifying the negative, or when this is not
possible to paint over it as well as possible.

Transparent spots are formed on the negative by an impure silver
bath or by dust flying about the room. These must be spotted out if
increased work later on on the stone or zinc plate is not desired.

In reproducing fine copper engravings, it generally happens that the
fine grey hair-like lines and the light interstices, if the plate was
not properly polished, appear less transparent in the negative than
the other parts of the picture. In developing the print the result is
a partly broken image which can only be retouched with considerable
trouble. The negative can be corrected by taking care to paint over the
transparent parts. Professor Husnik recommends, when the picture is not
too large, to fasten a transparent paper on the back of the negative,
and to cover over the glassy places with a soft lead pencil. These
parts then print simultaneously with the hair-like line and develop
also equally. If, however, the negative is large, and the picture very
complicated, a glass positive picture is prepared in the following
manner: A polished sheet of glass is levelled and coated with the
following solution:—

 Gelatine                    6 parts by weight.
 Sugar                       1 part by weight.
 Ammonium bichromate         1 part by weight.
 Water                      80 parts by weight.

When the solution has dried the glass plate is laid on the negative
and exposed till the deepest shadows have printed, and it is then
developed in water. When dry this glass positive is laid on the back of
the negative so that every part of each picture fits. The plates are
then bound round the edges with paper strips so that they cannot shift.
By this—although somewhat troublesome—operation can an unsatisfactory
negative be rendered more even.

This correction can also be effected in the following manner: The back
of the negative is coated with raw collodion which is faintly coloured
with aniline red, eosine or fuchsine, allowed to dry, and then with an
engraving needle or a narrow knife the less transparent lines may be
scraped out, so that the red collodion only remains on the transparent
places. Obviously also this can be done in the reverse, by painting a
faint red on the transparent places with a brush.

By this last method a tolerably extensive retouching may be {36}
effected on unequal negatives, which are the result of not quite
equally black or also very close drawn originals, from subjects
with very fine lines, such as copper-plate engravings, or from
finely-executed lithographs with very great reduction. Finally it
should be mentioned that with intelligent retouching any bad negative
can be used for photo-lithography, and the only question now is
whether it is not better to take the shortest way and prepare a
suitable negative when the original really permits of its being done.
In printing on chromated gelatine paper a good result can be easier
attained from somewhat foggy or thin negatives than by printing with
asphalt or other light sensitive substance.

The following kinds of negatives are used for the various
photo-lithographic processes:—

For the transfer process with chromated gelatine paper or direct
printing on stone or zinc direct, a reversed line or autotype negative.

For Orell and Füssli’s process, a reversed ordinary half-tone negative.

For Bartös’ process and for photogravure on stone, a direct ordinary
half-tone negative.


3. PREPARATION OF THE DIRECT GLASS NEGATIVE.

The preparation and cleaning of the plate glass is as follows:—First
of all the plates are roughened with a piece of sharp pumice stone on
the extreme edges to the breadth of about 0·5 cm. in order to prevent
the frilling or floating off of the collodion film. This is very little
trouble considering the advantage it offers. After being edged the
plates are placed in a solution of

 Nitric acid chemically pure         1 part
 Water                              10 parts

Instead of nitric acid, chromic acid may be used, but this is not
absolutely necessary.

After one or two hours the plates are taken out of the acid bath, well
washed under a strong water rose, and dried in a place free from dust.
Then the plates are well rubbed with 1 : 10 tincture of iodine solution
with a pad of clean filter paper and then polished with 50 per cent.
alcohol. This preparation must be done with absolute accuracy, and thus
they make all substrata of albumen, india-rubber solution, etc., for
direct negatives unnecessary.

Plates which have been previously used are placed in pure water till
the collodion film has become loose, and are then scrubbed with a stiff
brush, treated for some hours to a bath of caustic soda, and then
treated as above, when they may be used again. {37}

For reproduction of simple line drawings iodized collodion is used
which consists of 2 per cent. raw collodion composed of—

 Ether             1,000 ccm.
 Absolute alcohol  1,000 ccm.
 Pyroxylin            40 g.

Iodizing is done with

 Sodium iodide    15 g.
 Cadmium iodide   15 g.
 Cadmium bromide   8 g.
 Potassium iodide  1 g.

The last salt is dissolved in a few drops of distilled water, the other
salts are dissolved in one part of the absolute alcohol. The iodizing
solution is filtered into the raw collodion, which has already been
allowed to settle and filtered, and allowed to stand for some days.

The sensitizing solution is nitrate of silver in the proportion of
1 : 10, with larger sizes 1 to 12–1 to 14, and the silver bath is
faintly acidulated with chemically pure nitric acid.

For a monochrome subject the exposure lasts according to the size of
the reproduction, and the rapidity of the objective, from three to ten
minutes.

For development an iron developer is used, consisting of:—

 Water                  4000 ccm.
 Ferrous sulphate        150 g.
 Copper sulphate          75 g.
 Alcohol (40 per cent.)  250 ccm.
 Glacial acetic acid     125 ccm.

The iron developer, with addition of sulphate of copper, is to be
preferred for short exposures to iron and lead developer. If the
plate has been correctly exposed the image gradually appears after
a short time, and very soon gets vigorous. When the details appear
in the deepest shadows the development must be immediately stopped,
otherwise fogging will ensue. If the image does not gain vigour by long
development it was under-exposed; with over-exposure the image appears
quickly and remains thin. The developer, when fresh, works fairly
quickly; older developers work slower, but give very clear negatives.

For very fine line drawings or reproductions of copper-plate engravings
the developer is used somewhat weaker, and one-fifth of its volume of
water added. The development takes somewhat longer; the fine lines
remain, however, very clear.

After developing the plate is well washed and then intensified first
with a solution of—

 Water            5000 ccm.
 Ferrous sulphate  180 g.
 Citric acid        90 g.

{38}

to which a few drops of a 1 : 12 silver nitrate solution have been
added. Care should be taken that in the first intensification the
glassy places remain clear. When, therefore, the desired opacity
is attained the plate should be immediately washed. Too long
intensification fogs the finer lines.

The plate should be fixed with 5 per cent. solution of potassium
cyanide. For this, however, a concentrated solution of hyposulphite of
soda can be used.

After well washing, the negative will show, when examined by
transmitted light, whether the ground is opaque enough, or whether
a further intensification is necessary. With correct manipulation
this first intensification will be sufficient for fine, well-prepared
drawings.

If, however, the opacity proves to be too little, after thoroughly well
washing, the second intensification or blackening is effected with a
concentrated solution of mercuric chloride in distilled water, which is
allowed to act till there is a distinct precipitate and the film has
become grey. After well washing the plate is flowed over with solution
of thiosulphate of gold till the grey quicksilver precipitate has
become absolutely black. The gold solution consists of—

 (A.) Distilled water        1000  parts
      Chloride of gold          1  part
 (B.) Distilled water        1000  parts
      Hypo-sulphite of soda    10 parts

Immediately before use solution A is added with constant stirring to
solution B, and a few drops of ammonia added. If the desired blackening
is not effected with one application the operation must be completed.

The solution of gold, when kept in the dark, will keep a long time.

For fixed negative the following intensifiers have been used with good
results:—

1. Intensifier with pyrogallol.

 (_a._) Silver nitrate    5 parts by weight
        Distilled water  75 parts by weight

To this solution is added—

 (_b._) Citric acid          5    parts by weight
        Distilled water     75    parts by weight
 (_c._) Pyrogallol           1·25 parts by weight
        Distilled water    150    parts by weight

2. The hydrochinone intensifier recommended by Baron Hübl:—

 Hydrochinone    10 parts
 Water         1000 parts

To this as much acid is added as will keep the solution clear for {39}
five minutes, when it is mixed with a third of its quantity of 1 : 30
solution of silver nitrate. The addition of a few drops of sulphuric
acid or 5 parts of citric acid is generally enough. This intensifier
acts somewhat more delicately than the silver and iron solution,
and has the advantage over the pyrogallol that it can be applied as
frequently as desired in full daylight to the fixed negatives without
any danger.

3. The metol intensifier.

The negative should be developed with the above-mentioned iron
solution:—

 (A.) Metol              15 parts
      Citric acid        10 parts
      Distilled water  1000 parts
 (B.) Silver nitrate     10 parts
      Distilled water   100 parts

The negative must be fixed before intensification with hypo and well
washed.

A small quantity of solution A is poured over the negative to drive off
the water, and then it is intensified in the ordinary way with 10 parts
of solution A and 1 part of solution B.

Further intensification is effected, as described, with mercury, the
blackening with thiosulphate of gold.

When the negative is finished and dried it is coated with a solution of
gelatine 1 : 50, or a 1 : 15 solution of gum, in order to protect the
film, and the negative should be levelled and allowed to dry.

Good opacity in the ground and clear glass in the lines of the drawing
are the fundamental requirements of a negative for photo-lithography.
But drawings are not always prepared in such a manner that this can be
completely obtained. With flat drawings which are drawn in grey instead
of black the first intensification is only continued till the finest
lines appear clear. For further intensification the negative after
drying is given a coating of a light sensitive solution of—

 Gum arabic            17·5 parts by weight
 White sugar           17·5 parts by weight
 Potassium bichromate   5·8 parts by weight
 Glycerine              1·8 parts by weight
 Water                 35   parts by weight

Ammonia is now added till a light colour is formed. After drying it is
exposed from the glass side to 15° Vogel’s photometer, washed for about
a quarter of an hour and then soaked in warm water till a relief is
formed. By this operation a transparent relief is formed on the lines
of the drawing, which absolutely protects the same from fogging. The
intensification is then effected with mercuric chloride and chloride of
gold, or an intensifier of {40} solutions of uranium and ferridcyanide
is used, which is composed of two solutions—

 (A.) Uranium nitrate            8 parts by weight
      Sugar                      8 parts by weight
      Water                    350 parts by weight
 (B.) Potassium ferridcyanide    8 parts by weight
      Sugar                      8 parts by weight
      Water                    350 parts by weight

The negative is first flooded with the uranium solution and then with
the red prussiate.

Another process of intensification recommended by Prof. Eder and Toth
is the so-called lead intensifier.

The somewhat under-exposed negative ought only to be developed with
iron, fixed with hypo, and must then be well washed. It is finally well
rinsed with distilled water, and then placed in a filtered solution of—

 Lead nitrate               4 parts by weight
 Potassium ferridcyanide    6 parts by weight
 Distilled water          100 parts by weight

After a few minutes it becomes absolutely opaque in the covered parts.
The negative is allowed to remain in the bath till it has attained
the desired density. On the silver molecules of the image a pale
yellow precipitate has formed by the action of the lead bath. The
ferridcyanide of potash is reduced by the silver to yellow ferrocyanide
of potash, and gives then, with the lead salt, an insoluble compound,
ferrocyanide of lead. By the action of ammonium sulphide the unstable
lead salt is converted into a stable salt.

As soon as the negative has been taken from the lead bath and well
washed, till the washing water no longer gives a blue precipitate, it
is flowed over with dilute ammonium sulphide 1 : 5. Sodium sulphydrate
may also be used. The image becomes black instantaneously. The negative
becomes generally vigorous; if, however, it was exposed too long the
fine hair lines and points veil over very easily.

If the negative is not sufficiently intensified, which may happen with
very much under-exposed negatives, it should after well washing, and
before treating with ammonium sulphydrate, be laid in a bath of—

 Cadmium sulphate   10 parts
 Distilled water   100 parts

in which it becomes still whiter, and should then be treated with the
ammonium sulphide. The lead, the cadmium, and the silver of the bath
are converted by the ammonium sulphydrate into sulphide. The negatives
treated with cadmium have a yellowish tinge, whilst those treated with
lead are pure black. For {41} clearing up the white-lead image when it
is too vigorous or is foggy hyposulphite of soda or a dilute solution
of potassium cyanide can be used. This manipulation, however, requires
great care. The negative treated with ammonium sulphide if foggy can
be cleared up with hydrochloric acid, used weak and repeatedly poured
on and off, with careful watching of the action. After this it must be
well washed.

The lead solution will remain clear for weeks, and if it begins to
work slowly can be freshened up with addition of lead nitrate and
ferridcyanide of potash.

If stripping negatives are to be prepared, it is advisable, with the
lead intensified negatives, to give the glass plate a preliminary rub
with vaseline oil, to well wash, and then to coat with raw collodion.

Husnik’s graphite intensification is still to be mentioned, which, in
some cases, may be of great service, but requires practice and care.

The expert photo-mechanical worker will adopt one or the other methods
for his work, and as soon as he can work safely and without hesitation
he will adhere to that.


4. THE PREPARATION OF AUTOTYPE NEGATIVES OF BLACK AND COLOURED DRAWINGS.

As regards the preparation of autotype negatives from simple black
originals—wash drawings—the above photographic processes are quite
sufficient. For taking painted originals—such as oil paintings,
water-colour drawings, fresco, and pastell drawings—an orthochromatic
collodion must be used if a correct rendering of the tones in the
negative is to be obtained.

In our studio we have obtained excellent results with two kinds of
colour sensitive collodion. These are the isochromatic collodion
emulsion prepared by Dr. E. Albert and that suggested by Major von
Hübl. In using the former, the glass plates as soon as they are taken
out of the acid bath and well washed must be given a substratum of the
following solution:—

 White gelatine    5 parts
 Water           500 parts

to which is added—

 Glacial acetic acid  15 parts
 Alcohol              10 parts

The solution should be filtered and coated whilst warm, and the plate
dried in a room free from dust at least 15° R.

For the production of the sensitiveness, or for the production of the
correct reproduction of the colours, two eoside of silver dyes, R. and
P., are used. The P. dye gives great sensitiveness, and is especially
suitable for portraits, landscapes, etc. In using this a {42} correct
reproduction of the red must be abandoned, whilst the R. dye gives
an absolutely correct colour rendering but requires about double the
exposure. Ten ccm. of the eoside of silver solution are added to 100
ccm. of the emulsion. When coloured the emulsion will only keep for one
or two days.

The time of exposure with the R. dye is normally from one-and-a-half to
three minutes.

After exposure the plate must be well washed under a tap and then
allowed to thoroughly drain, or otherwise developing streaks will show.

Hydrochinone developer is used for developing, consisting of three
solutions:—

 (A.) Distilled water             500 parts
      Sodium sulphite             200 parts
      Potassium carbonate (pure)  200 parts
 (B.) Hydrochinone                 25 parts
      Alcohol (96%)               100 parts
 (C.) Ammonium bromide             25 parts
      Distilled water             100 parts

This developing liquid is concentrated, and is used as follows:—

 Solution A.  100 parts
 Solution B.    5 parts
 Solution C.    7 parts

To obtain hard negatives solution B is increased from 1 to 5 times. A
mixture of 150 parts of the above solution with 1000 parts of distilled
water forms the actual developer. By the addition of more concentrated
developer or increasing the quantity of water the developer may
be suited to the character of the subject. The developer must be
freely flowed over the plate, and then the plate fixed with sodium
hyposulphite. Intensification is effected with—

 (A.) Pyrogallol            7 g.
      Citric acid           7 g.
      Distilled water    1500 ccm.

and when dissolved

 Glacial acetic acid  25 drops

are added.

 (B.) Silver nitrate       10 g.
      Distilled water     100 ccm.

Immediately before use 100 parts of solution A are mixed with 5 parts
of solution B, and the intensification continued till the desired
density is obtained. Negatives can be reduced by placing them whilst
damp in a solution of—

 Potassium permanganate    1 part
 Distilled water         300 parts

When this has acted sufficiently, the plate is well washed, {43}
flowed over with a five per cent. solution of potassium cyanide, and
then well washed. When the dyed emulsion is used this must be done,
after developing, in red light.

A very excellent method of preparing an orthochromatic collodion
emulsion has been described by Hübl,[2] which can be used either wet
or dry. Repeated trials made in the Imperial Military Geographical
Institute, in our establishment, and in the Photographic Institute
in Vienna have proved the advantageous use of this method for
orthochromatic work. The raw emulsion, according to Hübl, is prepared
as follows:—40 g. of silver nitrate are dissolved in 50 ccm. of warm
distilled water, and as much ammonia added as will give a clear
solution; then 100 ccm. of alcohol are added and the whole allowed to
cool. 30 g. of ammonium bromide are dissolved in 35 ccm. of water and
70 ccm. of absolute alcohol with gentle heat.

  [2] “Encyclopædie der Photographie,” Heft 3, and Eder’s “Jahrbuch,”
  1892, p. 387.

To make the emulsion 450 ccm. of four per cent. raw collodion are
placed in a strong glass flask which will hold a litre, and to this in
the dark room the silver solution added. Some of the wool separates
out, but by vigorous shaking this can again be dissolved. A part of
the silver salt also remains suspended in the liquid in the form of
fine crystals. The ammonium bromide is added in three or four parts
whilst warm. After shaking thoroughly for several minutes the emulsion
is precipitated by distilled water, which is repeatedly added till the
separation is complete. The emulsion, which is now powdery, is placed
on a linen filter, washed several times with distilled water, squeezed
to press out the last of the water, damped two or three times with
alcohol, and then pressed. Whilst still damp with alcohol the emulsion
is dissolved in from 800 to 1,000 ccm. of alcohol and ether, mixed with
0·5 grs. of codeine, and allowed to rest for some days, when it will be
ready for use.

The preparation of the eoside of silver solution is effected as
follows:—10 g. of yellow-shade eosine are dissolved in 250 ccm. of
boiling water and 5 grs. of silver nitrate in 50 ccm. of water added
hot. The solution is allowed to settle, then filtered, and then washed
first with boiling water and then with alcohol on the filter, and then
dried in a dimly-lighted room.

To prepare the dye solution 0·5 g. of the dry eoside of silver and 1 g.
of ammonium acetate are gently heated together in 30 ccm. of alcohol
till dissolved, then 120 ccm. of alcohol and 10 ccm. of glacial acetic
acid are added, and the whole filtered. For plates to be exposed wet,
5–10 ccm. of glycerine are added. The emulsion is sensitized by adding
one-tenth of its volume of dye, and should be well shaken before
coating the plates. The glass plates should receive a preliminary
substratum of gelatine or india-rubber, so that the frilling of the
film and impurities of the glass plates may be totally avoided. {44}

For small sized plates the emulsion is used somewhat thicker than for
larger, and for the latter it should be diluted with alcohol and ether.
After coating they should be dried at about 15° C., and then for some
minutes exposed to a temperature of 30° C.

The plates should be developed with the following mixture:—25 g. of
sodium sulphite should be dissolved in 40 ccm. of warm water, then
10 g. of glycine added and 50 g. of potassium carbonate, at first in
small quantities in consequence of the evolution of carbonic acid. When
cool about 75 ccm. of a thin pasty liquid will be obtained, which may
be kept as a stock solution, and before use must be well shaken and
diluted with from 12–15 times the quantity of water. Wet plates should
be washed before development, and the developer flowed on; dry plates
should not be washed, and should be developed in a dish.

They should be fixed in sodium hyposulphite. The intensification may be
effected with metol (see p. 39), and the blackening as described on p.
38.

Obviously the collodion emulsion may be used for ordinary work undyed.

The qualities of the cross-lined screen and the distance of the same
from the sensitive plate will be described in Chapter V.


5. PREPARATION OF REVERSED NEGATIVES.

For the different photo-lithographic work direct and reversed negatives
are used; for the transfer process direct negatives are used; for
printing direct on to the stone or plate, reversed negatives.

For making the latter various methods are used, the principal of which
are as follows:—


(A.) EXPOSURE THROUGH A PRISM.

This method is, on account of its inconveniences and difficulties, only
used when it cannot be possibly avoided.

  [Illustration: Fig. 5.]

{45}

Fig. 5 shows the arrangement in which the prism _a_ is placed in front
of the lens _b_. The prism is three-cornered and the angle turned to
the objective is a right angle. The hypothenuse is silvered. It is
mounted in brass or nickel; on the mount is a screw, by means of which
it is fastened to the objective, so that the side opposite to the
hypothenuse lies upright to the side of the camera, and this position
must be an exact right angle to the focussing screen. The camera itself
must be absolutely horizontal. The subject to be taken, instead of
being in front of the camera, is placed sideways to the prism. The
image passes through _a′_, falls on the silvered hypothenuse _a″_, from
there through the objective _b_, through the box-shaped extension _c_
and the camera _d_, on to the sensitive plate, which is not visible in
the diagram. The exposure with the prism is about 1⁠/⁠5th longer than
usual, because a portion of the light is absorbed by the prism.


(B.) PLACING THE PLATE THE WRONG WAY ROUND IN THE SLIDE.

Generally, for making reversed negatives of line drawings, it is
quite sufficient to place the sensitive plate the wrong way round in
the dark slide or in the carrier, so that the film side, instead of
being towards the objective, is turned towards the operator. It is,
of course, absolutely essential to use only glass plates which are
absolutely clean and which contain no particles of sand, air bubbles,
etc., which would show on the prepared negative as points. After
sensitizing the plate, the back of it must be thoroughly cleaned, for
any smudges or drops would be visible on the negative. Obviously great
care should be taken also in cleaning the plate to make as little dust
as possible. In the Imperial and State Printing Works nearly all the
reversed negatives are prepared most satisfactorily in this way.

The photographic manipulations, the preparation, sensitizing and
developing of the plates, etc., is exactly the same as with direct
negatives.


(C.) STRIPPING NEGATIVES.

There are various directions for making stripping negatives.

An india-rubber solution, consisting of equal parts of benzole and
chloroform, in which an equal part by weight of india-rubber is
dissolved, is used as a substratum. When the solution has become quite
clear, the unreversed and unvarnished negative is coated with it. When
the film is dry, a coating of raw collodion, to which some drops of
castor oil have been added, is given. When this film is quite dry, it
is cut through near the edges with a sharp knife, and the glass plate
and film placed in a dish filled with water, when the negative film
will loosen from the glass and after some time will swim in the water.
In this operation the use of force must be avoided. The film is lifted
from the water by placing a card {46} underneath it, carefully dried
with fibre paper, then laid flat and pressed somewhat between tissue
paper. The negative prepared in this way has many disadvantages. First
of all, the film is easily injured, and, therefore, the edges should
be bound with strips of paper in order to protect it from tearing;
further, the film is easily folded and does not remain accurately of
the same size, which makes it useless for certain purposes. Moreover,
this process is somewhat costly. It is now almost entirely replaced by
a process in which a gelatine substratum is used.

This process is as follows:—The unvarnished negative is accurately
levelled with a level and coated 2 mm. thick with a solution of—

 White gelatine                20 parts by weight.
 Distilled water              500 parts by weight.
 Glycerine (chemically pure)   25 parts by weight.
 Glacial acetic acid           10 parts by weight.
 Alcohol 36%                   50 parts by weight.

The above quantity is quite sufficient for at least four negatives
21 × 26 cm. Many omit the acetic acid, but I have found that it is
an advantage for the slow drying, the pliability, and the keeping of
its size of the negative, to use acetic acid in moderate quantities.
To a certain degree the addition of glycerine also effects this, but
not sufficiently enough. Before pouring on the gelatine solution, the
plate must be absolutely dry. Any air bells formed whilst coating must
be pushed to the edge of the plate with a piece of card. The plate
must be dried spontaneously in a room as airy and as free from dust
as possible. In order to protect the film from dust particles, it is
advisable to give it a paper cap or cardboard cover, which allows the
access of air, and obviously it ought not to touch the film.

When the gelatine film has become thoroughly hard, it should be coated
with negative varnish, and, after again drying, should be cut round the
edges with a sharp knife right through to the glass and stripped from
the plate.

If the glass was well-cleaned and prepared, as has been previously
described on page 41, any gelatine film thus prepared will well and
safely strip without a substratum.

With dirty or old plates, a substratum of a 1–2% solution of
india-rubber should be used.

After stripping, the gelatine films are best kept between filter-papers
and under glass plates.

{47}




CHAPTER III.

PHOTO-LITHOGRAPHY BY THE TRANSFER OF A GREASY PRINT ON TO STONE OR ZINC.


1. THE HOME PREPARATION OF BICHROMATED GELATINE PAPERS.

Photo-lithographic or gelatine papers are articles of commerce and
entirely fulfil their purpose, and must before use be sensitized in a
bichromate bath. In establishments where much photo-lithographic paper
is not used, it is better to obtain it commercially from some reliable
firm and not to make it oneself, as this is somewhat troublesome, and
requires special appliances, some practice and experience, and with
small consumption does not pay.

For those who are interested in the preparation of chromated gelatine
paper I will now give the method, and I would remark that this paper
possesses all the necessary qualities for this process.

A sheet of well-sized paper is soaked in a bath of cold water, or
evenly damped with a clean pad, till it has become slimy. The water
is allowed to drain off, and then the sheet of paper placed on a
plate of glass which has been accurately levelled, and which rests
on a levelling stand with screws, so that it can be easily levelled.
By placing over it a sheet of blotting paper and squeegeeing with an
india-rubber or flannel squeegee the air bells between the paper and
glass are removed and any excess of water pressed out. Then the edges
of the sheet are bent up to about the depth of 2 cm., and wood or iron
rods laid outside, and a warm 1 : 30 gelatine solution poured on to it.
A sheet 70 by 70 cm. will require 305 g., that is 7·5 g. of gelatine
and 297·5 g. of water. The gelatine will set in a few minutes, when the
sheet is removed from the glass and laid on a rack in a place free from
dust to completely dry, and should remain from a day and a half to two
days. Such gelatinized sheets can be kept in stock, and will keep fit
for use in a cool, dry place for from six to eight months. For this
purpose only good pure rag paper should be used, as the ordinary cheap
papers contain many additions which render them unsuitable for this
work.


(A.) THE GELATINE.

The gelatine must possess certain qualities, of which the principal are
as follows. Before all things it must be pure and free from grease, or
else small round pits form on the surface, which give rise to troubles
in developing and printing, and only produce {48} defective transfers.
A large proportion of carbonic acid will produce the same faults, which
may, however, be remedied by a small addition of ammonia shortly before
use.

Gelatine is very hygroscopic, and therefore attracts moisture from
the room where it is kept and dissolves completely in warm water.
Even in very great dilution, _e.g._, 1 : 100, it sets again to a
jelly in the cold, but loses the setting power after being repeatedly
warmed, or if the temperature was raised considerably higher than was
necessary to melt it. Damp gelatine decomposes in the air very soon;
the decomposition, however, can be delayed with salicylic and carbolic
acids and glycerine. Greasy gelatine can be improved by the addition of
5 per cent. of alcohol. Too soft gelatine can be hardened with chrome
alum, and one part of chrome alum may be used to 200 parts of gelatine,
and by this addition the melting point is raised about 7° C. Too hard
gelatine gives rise to the formation of bubbles. If the gelatine
solution is slightly acid it is not a disadvantage.

The gelatine used in our establishment is of French make, and is
known as “transparent white gelatine,” and is also very suitable for
collotype. I mention this because the gelatine frequently gives rise to
failure. For practical work, then, it is advisable to stick to one make
when it has been proved to be absolutely satisfactory.

To those who would study more closely this very important material
for photo-lithography and collotype, I would strongly recommend the
brochure “Ueber die Reactionen der Chromsäuren und der Chromate auf
Gelatine, Gummi, Zucker und audere Substanzen organischen Ursprunges
in ihrer Beziehung zur Chromatphotographie,” by Professor Eder, in
which the most exhaustive information on the application of these two
materials so important in photography, gelatine and the chromate salts,
is given in a concise, popular, and easily understood form.


(B.) THE CHROMATE SALTS.

The sensitiveness to light of the different chromium compounds forms
at present the foundation of several photographic and photo-mechanical
processes.

According to Dr. Eder, Vauquelin discovered in the year 1798 chromium
and chromic acid, and made at the same time the observation that
chromic acid formed with silver a carmine red salt, which became
purple-red by the action of light. In the year 1832 the philosopher Dr.
Gustav Suckow, in his work, “Die chemischen Wirkungen des Lichtes,”
stated that the chromate salts were also sensitive to light in the
absence of silver if an organic substance was added, as in the light
lower (green) oxidation products were formed. In 1839 Ponton added to
Vauquelin’s and Suckow’s discoveries, and discovered the photographic
application of chromate of silver, the light-sensitiveness of potassium
bichromate on paper. The chromates are _per se_ stable in light; in
the {49} presence of organic substances, however, such as gelatine,
albumen, gum, etc., a quick reduction of the same takes place in light.
Talbot finally found that a mixture of gelatine and a chromate became
brown in light, and lost at the same time its solubility in warm
water and its power of swelling up in cold water. According to the
same authority simple potassium chromate is from 20 to 25 times less
sensitive to light than potassium bichromate, and the simple ammonium
chromate shows the same sensitiveness to light as ammonium bichromate.
For photo-lithography the latter salt, potassium bichromate, is very
important, and it has the chemical formula of K_{2}Cr_{2}O_{7}.


(C.) THE GELATINIZING.

The gelatinizing of the paper and the preparation of the gelatine
solution is effected as follows:—

The gelatine, accurately weighed out, is placed in small pieces in
the proper quantity of water, either in a large measure or some other
vessel, and placed in a water bath and immediately heated. It is
advisable to place the vessel containing the gelatine into the water
bath before the latter is heated, so that both may heat together and
fracture of the glass be thus avoided. When the gelatine is completely
dissolved the warm solution is filtered through a linen filter, and so
that it may not be cooled the vessel into which the gelatine solution
is filtered is also placed in the water bath.

Whilst still warm and liquid the gelatine is poured on to the
previously prepared paper, and any bubbles of air brought to the edge
of the sheet with a strip of stiff paper or a feather.

It should be especially noted the gelatine solution should be used up
as quickly as possible or else it will deteriorate. Gelatine which
remains for a long time in a state of solution becomes soft and fluid,
and if the chromate bath is not well cooled a partial or complete
dissolving of the same takes place in sensitizing or later in washing
and developing.


(D.) SENSITIZING.

The first thing to be treated of is the preparation of the bichromate
bath. The necessary quantity of the bichromate of potash is rubbed
up as fine as possible in a porcelain mortar with a little water; it
should then be transferred to a larger flask and the necessary quantity
of water added. When all the bichromate is dissolved the solution
should be filtered, and so much ammonia added as will convert the
orange yellow colour into a straw yellow. This bath can be kept, in a
dark cool room, fit for use for a long time. The proportions for the
solution are—

 Potassium bichromate   1 part
 Water                 15 parts

{50}

and as much ammonia as will make it straw coloured. The bath is
neutralized with ammonia or a soda or potassium salt, because solutions
of the bichromate salts have the property of dissolving gelatine even
in the cold.

The day before being used the sheet of gelatinized paper is placed in
this bichromate bath, which should be as cold as possible; in summer
it should be cooled with ice. It should be completely immersed in this
bath, so that the solution covers every part of the sheet to the depth
of 1–2 cm., and should be left in it about three minutes; care must be
taken that no air bells form on the gelatine. If this should happen
they should be removed with a soft brush, which ought not to be used
for any other purpose. On the places not covered by the bichromate
solution, which has been kept off by the air bells, the paper would not
be sensitive to light.

For ordinary printing the paper may be dried in the air by placing it
on a board, or better on a rack; for better class work, and actually
for all work, it is better to squeegee the paper as soon as it is
removed from the bichromate bath on a sheet of plate glass which has
been well cleaned and polished with talc, the excess of solution
or any air bubbles being removed by squeegeeing thoroughly under
blotting-paper. Many operators slightly grease the glass plate. I have
found that this is not necessary if a sufficiently cold sensitizing
bath is used, the plate glass thoroughly cleaned and well rubbed with
talc, and it is dried in an airy room. It is advisable to see that
there is always ventilation in the drying room, and the more this is
done the better the paper will behave in the subsequent operations.

To completely dry, the paper requires when drying by itself from three
to four hours; from ten to twelve hours when squeegeed to glass. The
best way is to sensitize the paper in the afternoon or the evening,
so that it may be used the next day in the morning. The paper when
sensitized will, when properly kept in a dark cool room, be in a fit
state to use for several days. By squeegeeing on to the plate glass
the paper takes a very high glossy surface, and thus in printing comes
into intimate close contact with the negative. In exposing, therefore,
every fine line appears with greater precision than on paper which has
become wrinkled and uneven, and which has not been previously glazed.
It should also be mentioned that this gloss is frequently obtained by
burnishing the sensitized paper when dry.


(E.) THE PRINTING.

After the paper has been sensitized and well dried it is printed.

The negative is first laid in the printing frame film side up. Then the
paper is laid with the sensitive yellow side on the negative, and the
frame closed. Before it is placed in the light, care {51} should be
taken to see that the paper lies closely everywhere on the negative,
otherwise it will in parts be indistinct, and the print be useless. For
estimating the correct exposure a photometer should be used, and I take
as an example Vogel’s Fig. 6.

  [Illustration: Fig. 6.]

When beautiful clear negatives are used they should be printed to 14
to 16 degrees Vogel. Obviously no strict instructions can be given for
every case, and it will be dependent on the quality of the negative and
the object.

If the negative has to be covered, or any other dodge used, the time
of exposure must of course be arranged accordingly. As a general guide
it may be stated that the details of the picture should appear brown
and distinct from the ground when the print has been correctly exposed.
This examination of the picture must be done in a dark room, and only
one side of the printing frame should be opened, so that the print
does not shift. If it is over-printed, the picture develops badly, the
lines become broader, the details disappear in the deep shadows, and
the ink adheres to the unexposed parts. If, on the contrary, it is
under-printed, the ink does not adhere well to the exposed places, and
washes off in developing from the fine parts. Practice, as with all
manipulations, is necessary, and therefore one must not be disheartened
by the first failure.


(F.) THE INKING UP AND DEVELOPING.

As soon as one is satisfied that the exposure is sufficient, the print
should be taken from the frame in the dark room. The next process
is inking up and developing. This is effected in various ways; the
ink is either spread on the dry print with a velvet roller or a thin
developing ink is used with a brush, or the bichromate is first washed
out and then the ink spread on. I prefer to ink up the print with a
velvet roller, on which is the developing ink, before washing. By this
method I obtain between ink and gelatine the soluble chromium film.
The print develops then very quickly and well. For this purpose it is
laid on a glass plate, a litho stone or any other flat surface, a small
quantity of good litho transfer ink is distributed on an inking stone
with an ordinary litho roller, and the velvet roller charged with the
ink {52} from the stone by rolling it several times over the stone.
The print is now rolled up with the velvet roller till it appears of
a general grey tone; the details of the picture, however, are still
visible through the ink. With this first inking up, too little rather
than too much ink should be used. When the inking up is finished, the
print should be laid in cold water, care being taken that no air bells
form on the surface, and it is also advisable to frequently turn the
paper over once or twice in the water. After ten or fifteen minutes a
change will be seen on the print, the exposed parts will be somewhat
more depressed than the unexposed, which will have swollen to some
extent in the water. The print is now taken out of the water and spread
out exposed side up on a sheet of glass, very carefully avoiding folds,
and dried with blotting paper, and the water which is on the back of
the print is removed by strong pressure on the print from the front.

The print whilst still damp is again for a second time rolled up with
the velvet roller, by which means the details of the drawing again take
the ink. From the unexposed parts the ink now goes on to the roller,
in exactly the same way as in cleaning the litho stone, and they
appear covered now with a very faint tone. If the first rolling up was
done with too much ink, it will be accompanied by two disadvantages.
Firstly, that too much ink will adhere to the details of the drawing,
and there will be the danger that in transferring the same will appear
thick, and secondly the tint will not be so well removed from the
unprinted parts, which will produce a difficult development. It is
therefore advantageous only to give in the second inking the printed
parts the quantity of ink requisite for transfer.

After being inked up a second time the print is again placed for a
short time in the water, then taken out, spread out on the sheet of
glass, and now completely developed with a pad or a tuft of cotton
wool. This is effected by going over all the print with light pressure
and not too quickly with a circular movement, till the drawing appears
quite clear and clean on a white ground. In this operation it is
advisable to use as much water as possible, in order to remove all the
bichromate from the print, which might be troublesome in the subsequent
operations. The washing should not therefore be stopped till the
unexposed parts have lost all yellow tinge and appear nearly white. If
the bichromate remains in the unexposed parts, the process continues
during the drying of the print; these places then become hardened, and
are frequently the cause of an unsatisfactory transfer. _One of the
chief requisites is, however, that too much ink should not be used in
inking up. The developed drawing should not appear deep black, but
grey, yet covered in all places._ The developing ink contains so large
a quantity of grease that the least quantity is sufficient to form the
combination previously described on the stone. {53}

The developed print is freed from all adhering water by pressure with
half-damp blotting-paper, and then fastened on to a board with drawing
pins to completely dry.

The room where the development is carried on should be well ventilated,
and not be heated too much, as the latter makes the work more
difficult. The drying ought not to be forced and should be allowed to
take place spontaneously at the ordinary temperature of the room.

For transfer to zinc and for sending photo-lithographic prints it is
advisable to bathe them in a 10 per cent. solution of alum for about
five minutes, so that the gelatine film is hardened. When the prints
are to be used or to be transferred to stone immediately this treatment
may be omitted without harm.


2. VARIOUS OTHER PHOTO-LITHOGRAPHIC PAPERS.

The paper described above is a pure gelatine paper, and although this
has proved in practice to be satisfactory for all work that may arise,
still I will describe some other papers, which have been also used in
practice with good results, and for those who do not care to prepare
their own paper they have the advantage that they may be obtained
commercially.

Albumen was used first instead of gelatine and rendered sensitive by
the addition of a chromium salt. This paper had the disadvantage that
it could not be kept, and only sufficient paper and albumen solution
for one day’s work could be prepared. A much greater disadvantage,
however, was that in developing, the albumen film was rubbed off with
the pad, and the paper was more or less rubbed up. A tint was produced
through this which transferred to the stone, and thus gave rise to
considerable troublesome and tedious retouching. This is not the
case, however, with the gelatine coating, which is comparatively more
resistant.


(A.) HUSNIK’S PHOTO-LITHOGRAPHIC PAPER.

Prof. Husnik has combined these two processes for the production
of his papers, as he gives a coating of albumen to a paper coated
with gelatine, which should be rendered sensitive with ammonium
bichromate. By this means is, on the one hand, the rubbing up of the
paper prevented and damage to the image not easily possible; on the
other hand, the development takes place very quickly, as the albumen
film dissolves and can be easily removed with the greasy ink. Husnik
specially contends that with the use of these papers he obtains
extraordinarily sharp images without any tint. The sheets thus prepared
will only keep, however, one or two days, and this inconvenient
operation has to be repeated every time before using the paper. This
applies also to the albumen solution, so Husnik has come to the
conclusion that it is better and more practical to use plain gelatine
paper; but {54} when trouble, time, and cost are not of such great
consideration, then it is better to use the paper with the compound
coating, as it enables less experienced operators to produce good work.

The paper more recently produced by Husnik is a pure gelatine paper,
which is rendered sensitive to light in—

 Ammonium bichromate   1 part
 Water                15 parts
 Alcohol (ordinary)    4 parts

As much ammonia is added to the bichromate solution as will convert the
reddish colour into yellow, and the bath smells of ammonia. The bathing
of the paper must be done as quickly as possible, and the sheet should
only be drawn through the solution. The exposure for this paper is
from one to three minutes in the sun, or from ten to thirty minutes in
diffused light.

The inking up of the print should be done with a greasy transfer ink,
to which one-sixth part of wax has been added, and the whole dissolved
in turpentine to the consistence of oil. The print is inked up with
this thin ink, and then gone over with a pad of cotton wool till it has
taken an even gray tint.

When the turpentine has evaporated the print is laid in cold water,
and, after about ten minutes, developed with a soft thick pad with
a continuous circular movement and quite light pressure. After
development all adhering water is removed from the print with damp
blotting-paper, and the transfer can be effected after from fifteen to
twenty minutes.

Husnik, however, did not rest, and soon prepared a still better paper,
which is known at the present time commercially as “Husnik’s Autotypic
Paper.” He produces this paper in large quantities, the coating of the
gelatine being effected by machines, which certainly tends to ensure
equality.

Husnik found that by the use of less concentrated bichromate baths
the fine lines were stronger after printing than from the nature of
the negative they should be. From one and the same negative there was
obtained by the use of a bichromate bath of 1 : 100 a relief five
times as broad as when a bath of 1 : 15 was used to sensitize the
paper. This he ascribes to the colour of the gelatine being less,
so that more rays of light penetrated to the surface of the paper,
from which it would be again reflected, and every point or line again
reproduced, which must obviously lead to an increase of the size of
the same; on the other hand, with strongly chromated paper, the rays
of light would not only be absorbed by the intense yellow colour of
the chromium salt, but still more by the brown tone formed immediately
after printing, which makes a reflection impossible. With autotype
negatives this is specially striking, as with weakly-chromated paper
black shadows without details occur, because here the quantity of light
is distributed by reflection over the fine points, and they will {55}
therefore become thicker. When using strongly-chromated papers the
details in the shadows appear open, clear, and sharp.

The concentration of the bichromate bath cannot be increased at will,
because other disadvantages are produced, especially such a firm
adherence of the greasy ink to the print that it transfers badly and
a part of it always remains behind. The bichromate salt, when as
strong as 1 : 18, dissolves the gelatine at ordinary temperatures, and
the baths, neutralized with ammonia, have the disadvantage that the
greasy ink adheres too little to the print and will be rubbed away in
developing the drawing. In order to entirely obviate the reflection
of the rays of light Husnik uses an addition to the gelatine besides
a 1 : 22 acid bichromate bath, which produces a pure yellow tone in
sensitizing the papers, is insoluble, and completely penetrates the
film of gelatine, so that a reflection of the chemically active rays is
entirely avoided.

This paper, which is also darker coloured, does not allow the light
rays to pass through, and is specially suitable for the transfer of
autotypes to stone or zinc.

For sensitizing this paper bichromate of potassium, sodium, or ammonium
is used, but the sodium salt has acted the best.

In winter a 1 to 20 bath is best; in summer, 1 : 22 or 1 : 24. The
treatment of the paper, as well as of the print, is exactly the same
as with other transfer papers. The bath will keep for fourteen days.
Caustic ammonia ought not to be used.


(B.) PHOTO-LITHOGRAPHIC PAPER BY ADALBERT FRANZ.

A photo-lithographic paper, with which I have obtained very good
results on stone as well as on zinc, with all kinds of drawings, is
sold by A. Franz.

This is also a pure gelatine paper. But Franz adds to the gelatine
solution manganese sulphate (this must not be confounded with manganese
borate, siccative powder, which makes the transfer ink dry so quickly
that a transfer to the stone or zinc is impossible).

Through the researches of MM. Lumière the manganese salts have
gained considerably in importance, and they have been introduced
into photo-mechanical processes. When an addition of about 10% of
manganese sulphate is made to the acid bichromate baths for sensitizing
photo-lithographic papers, the printed places assume a very much darker
colour, which is an advantage in judging the print, in developing the
finest lines, and points are retained much more easily than on paper
sensitized with the addition of ammonia.

This paper possesses the advantage, which is also more important, that
the—especially in summer—unpleasant ammonia bath need not be used. The
paper is sensitized in a solution of—

 Potassium bichromate    40–50 g.
 Manganese sulphate          5 g.
 Water                       1 litre

{56}

Ammonium bichromate ought not to be used. The bath would then become
cloudy immediately, and both bath and paper made useless.

When sensitized the paper can be kept from eight to ten days without
losing its good qualities.

With this a transfer ink is supplied in tubes, which must be mixed with
an equal volume of turpentine and benzine, so that it becomes quite
fluid. The print, when it is taken from the frame, is fastened on a
board with drawing pins, and with a fine camel’s hair brush coated with
this fluid ink as evenly as possible, and just so much that a light
grey tone is formed on the print. This paper must not be inked up with
a roller. As soon as the turpentine and benzine have evaporated the
print is laid in cold water, and after about ten minutes developed with
a clean tuft of cotton wool. The print does not show a strong relief;
the development takes place quickly and regularly. The ink, in spite of
its being so thin, is very greasy, so that only a very light skin is
necessary for the subsequent transfer. The tint produced by a negative
slightly too thin cannot be easily removed.

The other operations are the same as for the other photo-lithographic
papers.

Franz’s photo-lithographic paper is characterized, as already
mentioned, by giving extraordinarily sharp clean transfers, which,
indeed, maybe due to the use of the very thin liquid greasy ink. It is,
therefore, especially to be commended for very fine work.


(C.) ALBERT’S PHOTO-LITHOGRAPHIC PAPER.

August Albert’s is also a very good photo-lithographic paper. It can
be obtained commercially in two qualities, viz., “Photo-lithographic
paper” and “Autotypic high glaze paper.” This has been tested
in the K.K. Lehr- und Versuchsanstalt für Photographie und
Reproductionsverfahren in Vienna, and has received a certificate
of excellence. The high glaze paper has a prepared film of several
coatings; the developed prints when dry keep the high glaze.

The sensitizing bath consists of—

 Water                 16 parts by weight
 Potassium bichromate   1 part by weight
 Alcohol (ordinary)     4 parts by weight

and to this so much ammonia is added as will convert the reddish colour
into a light yellow; a small excess of ammonia does no harm. The
bichromate bath should not have a lower temperature than +15° R, or
else the solution cannot penetrate the film sufficiently, which results
in a defective development. The duration of sensitizing is from four to
eight minutes, till the paper is quite soft and damped through. It is
preferable to sensitize too long rather than too short. {57}

The paper should be squeegeed on to plate-glass, as already described,
and allowed to dry spontaneously. The paper when stripped from the
plate-glass shows a beautiful high glaze, and can be kept fit for use
for twenty-four hours. When the paper is older it can still be used,
but the development is more difficult, and it is better to avoid this
for fine drawings or autotypes.

Albert does not recommend a photometer to be used when printing this
paper, but by examination of the print to judge when this is correct.
The image should have a brown tone, and be easily distinguished by the
eye from the ground. Over-printing is disadvantageous, as the lines
and points become broader, the prints develop badly, the tint adheres
firmly to the ground, and the details in the deepest shadows are lost.

The inking and developing can be done by any of the known processes
which is thought desirable. The chief thing is that too much ink must
not be used in the first inking up; any intensification required may be
effected with a second coating. This is, especially for fine drawings
and autotypes, very important, whilst for coarser work also once inking
is sufficient. The prints are then placed in cold water, and after
sufficient washing should be developed with a soft pad or pad of wool,
with which any tint can be very easily removed from any parts which
should remain white.


3. THE PHOTO-LITHOGRAPHIC TRANSFER.


(A.) TREATMENT OF THE PHOTO-LITHOGRAPHIC PRINT AND THE PLATE.

The transfer from the bichromated gelatine paper requires generally,
as regards treatment and choice of the material, greater care on the
part of the printer than an ordinary transfer, and this increases in
transferring fine drawings or autotypes on to stone.

In the first place the good quality of the stone should be looked to.
For ordinary or coarsely drawn subjects this is of less importance,
but for fine drawings and autotypes it is of the highest importance.
Further, accuracy and cleanliness are all important, without which
successful work is impossible. On the other hand, a transfer can hardly
fail if it be accurately and correctly performed.

When the print comes from the developing bath, and has been well washed
so that every trace of bichromate is removed, it should be freed from
excess of water between blotting-paper. It should then be dried in a
not too warm place free from dust till the gelatine has completely set
and feels absolutely dry. The relief will have now again disappeared,
and the black and white places lie in the same plane. It is best dried
by pinning it to a board with drawing pins, and then set up in a dry
place.

In the meanwhile the transfer stone should be prepared, which must
be absolutely faultless. Just before the transfer it should be dry
polished with pumice stone, and then well dusted with a {58} cloth.
The slightest grain will give a spot in a fine tone. Obviously the
stone must be well ground so that neither any spots nor lines of
an earlier transfer can appear. With an open drawing this can be
corrected, but not with an autotype; in such a case the shortest way is
to make a new print and a new transfer.

The print is first wiped over on the back with a damp cloth, and then
laid on damp blotting-paper. After about five minutes the print is
treated a second time with a damp cloth, and then laid between damp
blotting-paper. It is not advisable to lay the print between ordinary
damp blotting-paper, as the gelatine becomes somewhat sticky, and would
attract particles from the rough paper.

The degree of dampness which is necessary for transfer may be judged in
that the print must feel soft, but the gelatine film ought not to be
very sticky. Any further preparation of the print before transferring
to the stone is not necessary. The print is laid on the stone, over it
a dry sheet, and then the cover, and then drawn through the first time
with light pressure.

In order to prove whether the transfer has taken well a corner may be
lifted up. All the ink which was on the print must be transferred to
the stone, and then the transfer has been completed in the correct way.
The print is now pulled off the stone and the transfer made ready, like
any other.

With this method of treatment the print will strip easily, which is not
the case if it was not well dried after the developing bath; a much
sharper and cleaner transfer will also ensue. If the print was too damp
a fuzzy, broken-down transfer will be obtained, because the gelatine,
which has become too soft, will be broken down.

I will also mention that it is not advisable to treat fine drawings or
autotypes with the rubbing-up pad. It is better to go over the transfer
with the roller, and the tones are kept cleaner. The stone is then
gummed, placed on one side, and allowed to stand some hours before
being etched.

For transferring to zinc plates which are to be etched or to be
printed from, the bichromated gelatine print should be bathed in a ten
per cent. solution of alum, allowed to dry, and then, as previously
described, damped, and then transferred under the same conditions as to
stone.

It only remains to mention that the stone or zinc plate should not be
too cold.


(B.) FAILURES IN THE PHOTO-LITHOGRAPHIC TRANSFERS.

The failures or faults which are met with in photo-lithographic
transfer may be caused by various things.

The squashing down rarely happens with photo-litho transfer, because a
good photo-lithographic paper will bear a considerable {59} amount of
dampness. When, however, it occurs it may be assumed that either too
strong pressure or insufficient care in the setting of the stone is the
cause. Much more frequently it happens that some parts of the print do
not transfer at all, or only in a defective manner. The chief reason
of this is that the print was insufficiently damped. This frequently
happens if ordinary or gravure prints are to be transferred with
photo-lithographic prints. If the printer encloses the impression on
the ordinary transfer paper and the photo-lithographic together in the
same damp sheet, and if he estimates the degree of dampness from the
gravure print, the photo-litho paper will be insufficiently damped and
a good transfer will not be obtained from the latter. If, however, he
waits till the photo-litho paper is damp enough, the other impressions
will be too damp and will squash out in transfer. For such work the
print on ordinary transfer paper and the photo-lithographic print
should be kept separate, so that the different dampness requisite for
each can be regulated.

Another case which frequently happens is that the print is contaminated
with particles of dust or other foreign substances. These may be flying
about in the air or be on the stone, the roller, or the damping paper.
Through this many transfers of fine drawings are rendered useless.
Perfect cleanliness of the utensils and the use of the correct ones,
combined with a drying-room for the print absolutely free from dust,
are absolutely essential for faultless work.

The composition of the ink, especially if it was too hard, may give
rise to bad transfers.

Photo-lithographic papers, which are prepared with very hard gelatine,
must be laid before transferring in lukewarm water. By this means the
hard gelatine becomes rather sticky, and the greasy ink transfers much
better. Even those points which in developing have taken up little ink,
and appear grey, transfer completely to the stone and adhere firmly.

{60}




CHAPTER IV.

PHOTO-LITHOGRAPHY BY DIRECT PRINTING ON TO STONE OR ZINC.


The processes of photo-lithography previously described are based upon
the printing on to bichromated gelatine or albumen paper development
with a greasy ink and subsequent transference of the greasy print to
plate or stone. A process may also be used in which the stone or plate
is printed on direct. There are in this various methods, of which the
principal are printing on to light-sensitive asphalt, or an organic
substance, gelatine or albumen, in combination with a bichromate
salt. The reason is the high sensitiveness, which is possible, of the
substances used.


1. THE ASPHALT PROCESS.


(A.) THE LIGHT-SENSITIVE ASPHALT.

Light-sensitive, or so-called Syrian, asphalt, which is prepared for
photo-lithographic and photo-zincographic purposes, can be obtained
from various firms who deal in photographic goods, and one has only to
dissolve the same according to the prescribed directions. This kind of
asphalt is, however, not very sensitive, and in use must be printed
for some considerable time. If, therefore, an asphalt of greater
sensitiveness is desired it is not sufficient to merely dissolve Syrian
asphalt, but it must undergo a preliminary preparation.

Only that part of the asphalt is sensitive or useable for
photo-lithographic work which does not dissolve in ether. The
insensitive part must, therefore, be separated out, which is done by
finely powdering the asphalt, sifting it through a fine sieve, and
then treating it with ether. All that is soluble in ether goes into
solution; the marc which is not soluble in ether is then dissolved in
benzole and used as wanted.


(_a._) HUSNIK’S PROCESS.

Professor Husnik has improved this process in so far that he does not
dissolve the asphalt powder in ether, as, according to his view, a
complete solution of all the insensitive portion is not attained by
this process, but he dissolves coarse asphalt powder completely in
rectified spirit of turpentine to the consistence of a moderately-thick
syrupy mass, until no hard particles or a residue are contained in the
solution. To this viscous asphalt solution a plentiful quantity of
ether is added gradually, and with constant stirring, and a big flask
should be used for this purpose. After a sufficient quantity of ether
has been added a pitch-like deposit {61} separates out at the bottom.
In order to test whether there is still any light-sensitive asphalt
in the supernatant liquor a small quantity is poured into a glass and
mixed with ether, when if a precipitate ensues more ether must be added
to the big flask.

After standing for about twenty-four hours the ether contains all
soluble insensitive constituents of the asphalt; the pitch-like residue
in the flask, after pouring off the solution, is again treated with
ether, so that all turpentine is extracted and any stray insensitive
particles are dissolved. The pitchy residue is now removed from the
flask and allowed to stand in a porcelain dish in a warm place, with
frequent stirring, till it is quite freed from ether, and has formed
a hard, brittle, black shining substance, which can be easily broken
up into powder with the hand. This product is now the light-sensitive
asphalt, which is dissolved for use in anhydrous benzole. As benzole is
only to be obtained anhydrous with difficulty, some chloroform is added
to the solution in order to prevent the running together in drying,
whence the film would become unequal and patchy.

The coating of the stone or plate with the asphalt film is very simple;
it should be placed horizontal, and then whirled rapidly on a whirler.

Printing under a clear negative takes from a quarter to half an hour in
direct sunlight.

The picture is developed with turpentine.


(_b._) VALENTA’S PROCESS.

Valenta recommends for photo-lithography asphalt which has been
sulphurized by the wet process, as it possesses a considerably higher
light-sensitiveness than that which is not sulphurized.[3]

  [3] Eder’s “Jahrbuch der Photographie,” 1892, p. 241.

The process is as follows:—100 g. of raw Syrian asphalt are boiled in
a retort with an equal quantity of raw pseudo-cumene, which has the
formula C_{6}H_{3}(CH_{3})_{3}, and a boiling-point of about 170° C.,
with 12 g. of flowers of sulphur, which should have been previously
dissolved in the pseudo-cumene. When after about three or four hours’
boiling the evolution of sulphuretted hydrogen has ceased, the
pseudo-cumene is distilled off and the black pitchy residue dissolved
in benzole in the proportion of 4 : 100, and used for the preparation
of the plate or stone.

The sulphurized asphalt prepared in this way is almost insoluble in
ether, but dissolves fairly readily in benzole, toluene, xylene,
cumene, and turpentine, and is very sensitive to light.

With this asphalt good prints are obtained even in bad, cloudy weather.
For use four parts of the sulphurized asphalt are dissolved in 100
parts of benzole, the solution filtered and diluted till a thin film
on a zinc plate shows a golden yellow colour. Exposure of the asphalt
solution in an open flask for from half to one hour in sunlight is
advisable.

For developing the asphalt image rectified oil of turpentine free {62}
from acid is used; the best is French or Austrian. The development
may be accelerated by adding Hungarian or Russian turpentine, which,
however, attack the asphalt image; it can be restrained by the addition
of ligroin, benzine, or wood oil to the turpentine.

Zinc plates are best developed in a dish, stones by making a wax margin
round the drawing. The oil of turpentine is poured on and rocked to
and fro. Rubbing with a pad of cotton wool, etc., should be avoided.
After development the plate should be well washed under a stream of
water, and before gumming, the plates should be exposed for some time
to light, as this makes the ground more resistant to the etching.


(B.) COATING THE STONES.

The stone or zinc plate is now coated with one of the above-described
asphalt solutions, or with the following:—

 Asphalt           20 g.
 Chloroform       300 g.
 Benzole          100 g.
 Oil of Lavender   20 drops.

The solution must be thin, so that it flows over the stone well and
does not form unequally-covered patches.

The subsequent manipulations must be conducted in the dark.

The stone which is to be used must be well ground, and polished with
dry pumice stone, well dusted, and be absolutely flat. It ought not to
have any depressions, as the negative would not lie in contact there.
The places would not print sharp, and therefore a bad result would be
obtained.

The necessary quantity of the solution is now poured into the middle
of a well-polished stone, and distributed as evenly as possible by
rocking backwards and forwards. When thoroughly distributed the stone
should be placed on the whirler and kept for some time in motion.
The asphalt solution must be as thin as possible, so that it appears
yellowish-brown and the colour of the stone appears through it. If the
stone is only covered all over the film can be very thin; on the other
hand, if it is too thick it will not print through, and will develop
badly, as too much of the asphalt will dissolve. If zinc plates are
used for printing they should be prepared as previously described on p.
6. Zinc plates for deep etching must be well ground and well polished,
and ought not to repel water. The zinc plates are coated the same as
the stone.


(C.) PRINTING.

When the film is absolutely dry, which will be in about fifteen
minutes, printing may be proceeded with. For this purpose the negative
is either laid on to the asphalted stone, film side down, and pressed
down with screw bands, or it is laid, the glass downwards, in a
specially-constructed and very strongly-built printing frame, which is
provided with a sheet of plate glass, and the {63} asphalted side of
the stone laid on this, the printing frame closed, and then exposed to
light. The exposure continues according to the strength of the light
and the nature of the negative from 15 minutes to 1½ hours. If the
film of asphalt be thin and the negative clear it may be printed to
18 or 20 degrees in Vogel’s photometer. This kind of printing always
requires some experience, as various factors, such as the thickness of
the asphalt film, the density of the negative, also the fineness of the
drawing, have to be taken into account. It will be understood that the
asphalt film must always be coated as evenly as possible.

If it is printed too long the stone will not develop at all, or only
in parts; if it is printed too little the drawing wholly or partially
dissolves. In both cases an unsatisfactory result will be obtained.
Negatives very clear in the lines of the drawing, and well covered in
the ground, are here more essential for success than with the chrome
gelatine process.


(D.) DEVELOPING AND INKING UP.

When properly printed the frame and the stone should be brought into
the dark room and development proceeded with. For ordinary Syrian
asphalt rectified turpentine can be used, and one of two methods may be
adopted. The stone is laid in a pan as straight as possible, and then
flowed over with turpentine, which should be allowed to remain on it
for some time, and then poured off into the pan. Fresh turpentine is
now applied till the drawing appears clear and distinct. The turpentine
which is allowed to run off can be used for washing purposes. An edging
of warm gutta-percha may also be made round the drawing, and then
turpentine poured on to it and the stone rocked up and down till the
drawing is developed.

The very sensitive kinds of asphalt of Husnik and Valenta are much
more readily soluble than the ordinary Syrian asphalt. In developing
one must go carefully to work, and not allow the turpentine to stay on
the stone a long time, but to pour it over the stone, which should be
inclined so that it can run off. This can be repeated if required. It
can be well and safely developed if half and half of turpentine and
linseed oil is used, which, however, has the disadvantage that the
stone becomes greasy, but this can be taken off by the expert printer.

After developing the stone should be well washed under a strong stream
of water, then allowed to dry in the light, as by this the asphalt film
becomes more capable of standing the etching, and then be coated with
neutral or very slightly acidulated gum. After gumming, the stone is
again dried and allowed to stand for some hours to rest, after which it
can be inked up and etched, and finally sharp etched.

The zinc plate is, after development, also well washed, then allowed
to dry, treated with thin gum solution, then with an {64} etching
solution of tincture of galls or gallic acid and phosphoric acid, and
inked up.

Prints on zinc plates for deep etching are gummed after developing, and
if the asphalt film is perfect without rubbing up with a pad, which
thickens the drawing, etched for some minutes in very dilute nitric
acid.

Many lithographers are accustomed, and indeed it is necessary with some
transfers, to rub the prints up with greasy ink. The process is as
follows:—Greasy transfer ink is diluted with some turpentine, and after
the stone has been gummed and allowed to dry, then washed, the drawing
is wiped over with a soft pad with this dilute ink, when the ink
adheres to the drawing, strengthens it, and if great care is not taken,
thickens it also. With asphalt prints this is absolutely useless, and
for other direct prints, as well also as for good chromated gelatine
prints, in most cases unnecessary. The exposed asphalt combines so
intimately with the stone that strengthening with a greasy ink is quite
unnecessary, is indeed absolutely purposeless, as the ink can neither
penetrate the hard asphalt film nor combine with it. The film of
asphalt alone is so resistant to every etching solution that it is for
this reason absolutely useless to strengthen it.


2. OTHER PROCESSES.

Besides the asphalt other mixtures of other light-sensitive substances
may be used for direct printing, and these are mostly organic
substances in combination with a chromium salt, and possess also a
greater sensitiveness to light than asphalt.

The solutions which have been specially used in our establishment
consist of—

 (A). Albumen                    5 g.
      Ammonium  bichromate       3 g.
      Distilled water          500 g.
      Ammonia                15–20 drops
 (B). Chloroform               250 g.
      Benzine                   50 g.
      Alcohol                   20 g.
      Mastic                     2 g.
      Aniline red                2 g.

Solution A is strongly sensitive to light, and is used for coating
the stone or zinc plate; with solution B the stone is coated before
developing. The details of the process are as follows:—


(A.) COATING THE PLATES.

After the stone has been carefully polished and well dusted it should
be first flowed over with distilled water, in order to increase the
possibility of spreading the sensitive solution. When the water has run
off, the stone whilst still damp should be flowed over with solution A,
and care should be taken that the same is evenly distributed and that
no bubbles form. The stone should be {65} placed immediately on the
whirler and rotated till the solution is dry. Obviously a thick film
must be avoided, as in such a case the print would not adhere to the
stone.

If a zinc plate be used it must be well prepared and be rendered free
from grease. To prove this the plate is flowed over with distilled
water, and when this spreads equally all over and is not repelled
from any part, the solution can be poured on. If, however, the plate
does not willingly take water everywhere, it must be again cleaned or
polished. The other operations are the same as for the stone.


(B.) THE PRINTING.

When the film is quite dry, printing may be proceeded with. The
duration of printing depends obviously also here again on two important
factors—the quality of the negative and the strength of the light.
Under a good negative with absolute bare glass in the lines of the
drawing I print to about 10° Vogel, for example:—

 In direct sunlight (middle of April, 11 a.m.)        2 min.
 In the shade       (middle of April, 11 a.m.)        5 min.
 In electric arc light (3000 c.p., at a distance of
      50 cm. = 20 ins. without reflector)            25 min.

The picture is faintly visible. If the negative was too thin, or if
it be over-printed, the image develops badly or not at all. With
under-printing the film washes right away.

Immediately after printing the stone or plate is coated with solution
B, which is distributed as evenly as possible by rocking backwards and
forwards. It is not necessary, however, to obtain even distribution
with a whirler. The whole of the coated surface becomes deep violet.


(C.) THE DEVELOPMENT.

When solution B has become completely dry, the stone is placed in a
suitable vessel with pure water. After about five minutes the places
not affected by light dissolve if the stone is rocked, and it is only
necessary to go over the drawing with a pad of cotton wool to clean
the same completely. The drawing now appears a deep violet on a bright
ground. The development is continued without rubbing strongly with the
pad—which might rub up the drawing—till all the details of the drawing
appear clear and distinct. This especially applies to the details in
the deep shadows.


(D.) FURTHER MANIPULATIONS.

When the stone or plate is correctly developed, which can be easily
told, it should be well rinsed and again exposed to make the film
adhere firmly. It should then be gummed and treated as previously
described in the asphalt process. The “rubbing up” of the stone or
plate is not necessary; it is better to roll up the drawing with an ink
roller. Zinc plates for deep etching can be lightly etched, then dusted
with fine asphalt of resin powder, heated and then further etched. {66}


R. J. Sachers, of Toronto, Canada, published a sensitive solution which
has the following composition:—

 Distilled water         150 parts
 Fish glue                50 parts
 Ammonium bichromate       2 parts
 Ammonia                   2 parts
 Chromic acid              1 part

This solution is brown, not very transparent, with an olive green
tinge, and must stand and settle at least twelve hours before it can be
decanted, filtered, and used. The time of exposure is about—

 Direct sunlight                          2–5 minutes
 Diffused light                         12–15 minutes
 Electric arc light (3000 c.p., 50 cm.)    30 minutes

The image appears a bright brown on the golden yellow ground of the
plate. The development is effected in an aqueous solution of methyl
violet, when the image assumes a beautiful blue violet colour. The
developed image is hardened with alcohol. The results by this method
are very good, and although this is recommended for half-tone etching,
it is also suitable for photo-lithography.

Excellent results also attend the sensitive “Marine glue solution,”
prepared by A. Hebensperger, of Munich, to which a second solution
called “Chlorogutt-losung” is added. The sensitiveness to light is very
high, and the treatment about the same as with the first described
substance. The “marine glue solution” consists of albumen, bichromate
of soda and ammonia. The dye solution of Victoria blue dissolved in
benzine.

The process published by Waterhouse consists of coating a prepared zinc
plate with a thin chromated solution, and then drying in a few minutes
with a gentle heat—

 (A.) Arrowroot                 2 parts
      Potassium bichromate      9 parts
      Water                   700 parts
 (B.) Alum                      1 part
      Water                     1 part

For use mix—

 Solution A                    40 parts
 Potassium bichromate           5 parts
 Solution B                    15 parts

This is printed under a reversed negative for about six minutes in
the sun. The plate is then laid for about half an hour in cold water
in order to remove the chromium salts, and then cleansed from all
soluble parts with a pad, and after well washing set up to dry. It
is then inked up with transfer ink, and after about fifteen minutes
washed with turpentine. This process, as, indeed, all direct printing
processes, offers many advantages for preparing colour plates from a
coloured object with one negative. The register of the separate plates
is very exact, which is not always the case with a transfer process. In
reproducing line drawings the unnecessary parts on the stone or plate
can be covered.

{67}




CHAPTER V.

THE HALF-TONE PROCESS FOR PHOTO-LITHOGRAPHY.


The half-tone process is used in photo-lithography to reproduce
originals which do not contain distinct lines or points, but closed
tones, which are executed either in one or several colours. With this
process any coloured picture, oil, water, pastel, indian-ink or sepia
drawing, as well as any photographs from nature of living, moving
scenes, or still life objects can be prepared for reproduction on the
printing press.

I will first describe briefly the theory of the process, and then come
to the practical part.

As regards the photographic part and the quality of the negatives, in
the present state of this method of reproduction the same principles
apply as in line reproduction; where they differ I will mention the
same.

The duration of printing, the transfer of the image to the stone, as
well as the other arrangements will be described in the different
processes.

We divide this chapter again into two sections:

1. Methods in which the half-tone is broken up when making the negative.

2. Those methods in which the formation of the grain is effected after
the negative has been made by some suitable means.


1. BREAKING UP THE HALF-TONE ON THE NEGATIVE (AUTOTYPY).

Of the various methods by which a breaking-up of the half-tones can be
obtained, the so-called “autotypy” is the one most used practically.
With this process the half-tones are broken up in the negative.

As every important technical discovery is formed not at once, but
must be made by a longer or shorter series of smaller discoveries or
improvements in order to attain the hoped-for goal, so was it also with
autotypy.

From the work of Paul Pretsch, Mariot, Brown, and Fred. E. Ives the
present state of the certain and beautifully-working half-tone process
gradually evolved, and the last process, which ought to be considered
as the immediate predecessor, is far outshone by autotypy as now
practised.

Early attempts were made to obtain a printable image on stone by
breaking up the chromated gelatine film, so that an irregular so-called
serpentine grain was formed on it, which corresponded {68} fairly
well with the theory of lithography, but gave no precise lines and no
beautiful gradations of stone. If the grain was somewhat too coarse the
effect of the picture was lost, the tone gradations were too far apart,
and only light and shadows were given; if the grain was too fine the
stone was not printable.

A further experiment was printing a design over the original, the
strength of which had to be brought in correct proportion to the
original; the impressing of a design was also tried, and when using
this method the correct angle of the incident light when making the
exposure had to be taken into account.

Further experiments, which were principally carried out by Mariot,
Cronenberg, and others, were founded principally on the basis of
breaking up the tones in printing. For this a lineature or screen on
glass, or a gelatine film, was introduced between the negative and the
sensitive film. Others, again, coated the blank glass plate with a
lineature, and prepared the plate afterwards with collodion or gelatine
emulsion for the exposure.

It will be thus seen how this method of reproduction developed step
by step till net-work of silk muslin or woven horsehair, and finally
grating images, strongly reduced by photography, were placed in front
of the photographic plate.

Thus were efforts made to make half-tone pictures suitable for printing
by litho- or typography, and although the end was very nearly attained,
yet the crux was not quite solved. These methods did not, however,
yield the desired result, namely, a beautiful sharp clear image. There
was still required a considerable improvement of the existing methods,
and this was made by Meisenbach, of Munich.

The principle by which Meisenbach prepared his images was essentially
different from the previously-described results. He broke up the
half-tones, also by means of a lineature, into a printable grain,
but the process was essentially different from the previous methods,
in that Meisenbach used a glass plate on which, on a black ground,
a grating was drawn till the glass was laid bare, and in this way
prepared a lineature which consisted of clear glass, transparent lines
and absolutely opaque lines.

He produced, first, an ordinary negative, from this a positive, and
from this, by the interposition of the lineature, the actual half-tone
negative for making the printing plate. The lineature or screen was in
the second exposure interposed before the sensitive plate, and half the
time of exposure given; then the screen was turned till the line first
obtained crossed the second at an angle of 90°, and then the exposure
was completed. By this means an absolutely certain breaking up of the
half-tones into mathematically exact points was attained, and the most
important step made in making photography useful for preparing printing
plates for the two principal methods, typographic and lithographic.
Meisenbach has called his process “autotypy.” It was, indeed, {69}
somewhat inconvenient, but had the advantage that on the negative and
also on the positive any retouching that was necessary could be done.

I cannot here enter into the numerous simplifications and improvements
of Meisenbach’s process which, as well in the photographic process as
also in the preparation of the lineature, were in the course of time
made partly by him and partly by Carl Angerer, Gillot, Bussod and
Valadon, Lefmann, and others, since, on the one hand, it would carry us
too far, and, on the other hand, they may be considered as a natural
consequence of the discovery. I will only mention that it was found
after a short time that the two exposures and the production of the
necessary positive could be omitted, and that the lineature could be
simply interposed before the sensitive plate in the first exposure, by
which an important simplification of the work was attained, and, thanks
to the continued perfecting of the processes, no detraction of the good
results was thus produced.

I do not consider it superfluous to give a short explanation of the
action of the interposed lineature on the photographic plate during
exposure.

If we take, for the sake of simplicity, not a picture, but a scale
with four or five-tone gradations from light to deep black, the light
tones will act more or less on the sensitive photographic plate
according to their degree of brightness, but as the rays of light have
to pass through the cross-lined screen interposed between the lens and
sensitive plate, and as the rays can only pass through the transparent
parts and not through the opaque, no homogeneous surface is obtained
on the negative, but a tone produced by the cross-lines of the screen.
If the tone was very bright, the rays reflected with great intensity
on the sensitive plate will completely decompose the silver film.
Since they are prevented by the screen from acting with equal power on
all places of the surface, these places will show very plainly on the
negative, and the result is therefore a darker tone on the same, which
is marked with bright fine lines, corresponding in thickness to the
screen plate.

If the original tone was darker so many rays of light will not be
reflected, and these have thus not the power to impress the screen on
the sensitive plate in full intensity; the result is therefore on the
negative a tone which does not contain such strong dark lines as the
first; the tone appears lighter in the negative, and in the print from
the same darker than the first.

In the reproduction of deep black surfaces finally no rays of light are
reflected, therefore no rays of light can penetrate through the screen,
and because actually here no chemical change of the light sensitive
film takes place, we obtain a negative which is clear and transparent
in these places, that is to say without any interruption, which gives
in the print a full black tone. {70}

In this process there comes, however, to our aid a very important
physical law, namely, the diffraction of light. A ray of light passing
through a round hole or a slit and falling on to a black surface is
represented not the same size as the slit, but more or less broadened
the more the receiving surface is moved away, and in the middle the
brightest light will be, and this gradually fades off into shadow
towards the margin.

If we take now the opposite, and use instead of the hole or slit a
black surface or a conglomerate of such in the form of points, squares,
or other geometrical figures, and if these be placed before a screen
illuminated with a bright light, these figures become somewhat smaller
with this bright illumination, whilst with a weaker illumination they
are represented in correct strength.

Where the light acts in its full intensity, or in excess, in a
manner of speaking it is diffracted or bent over the figures, and
proportionately makes them smaller.

This law does good service in autotypic work.

As we have seen, the rays of light must pass through the screen during
exposure. This screen consists of equally thick opaque black and
transparent white lines. Where the light acts with full intensity it
will be more diffracted over the black lines. It makes the lines of the
screen broader on the negative, and will, therefore, have more covered
places, which in the after printing of the prints cannot be penetrated
by the light, and thus represent the light places in the print covered
with fine dots.

The darker the tone the less the rays of light reflected, and the
less, therefore, can the light be diffracted. As the tones get darker
the lines of the screen become of equal value on the negative, till
finally, when at the opposite end of the screen, they totally disappear
in the deep blacks.

A valuable quality of a correctly-prepared autotype is, therefore, that
the covered lines or the covered grain appear of different strengths on
the negative. In the high lights they are stronger, in the half-tones
weaker, till finally in the black parts they have totally disappeared.

A further not less valuable property is that the grain in the highest
lights is not sharply defined, does not appear as a square point, but
is rounded by the diffraction of light, which gives a softer, more
beautiful appearance and plasticity.

Whilst the light reflected from the brightest parts of the drawing acts
with full intensity, and is diffracted over the figures standing in its
path and makes the same smaller, and cuts off the sharp corners and
gives more covered surfaces to the negative, as it decreases according
to the more or less deep shadows of the drawing, and can only act now
with less intensity through the open places of the screen, the result
is that the points become larger, till finally in the deepest parts it
is quite inactive, and the shadows begin to block. The action of the
light rays of different {71} strengths reflected on to the negative
in accordance with the brighter and darker tones of the drawing,
taking into consideration the print, can be graphically represented
as a pyramid of which the base represents the deepest shadows and the
point the high lights. If we interpose a cross-lined screen, or more
correctly called a grain plate, before the sensitive plate, we obtain,
graphically considered, grain figures, actually of many more very
different sizes, as shown in Fig. 7, 1–6, in which the smallest points
represent the high lights of the drawing, and those becoming gradually
bigger the gradually increasing shadows.

  [Illustration: Fig. 7.]

The original grain plate contained, measured diagonally, five black
points, five white interstices to the millimetre. The figures represent
enlargements of a negative made with the above-named grain plate, and
for this the grain plate was one millimetre distant from the sensitive
plate.

The accompanying Figure 8, 1–6, represents very much enlarged the
scheme of grain of an autotype from a perfectly-executed wash drawing,
with a screen of five opaque and five transparent lines to the
millimetre, in equal proportions of black and white, at a distance of
one millimetre from the sensitive plate, with equal time of exposure
before and after the turning of the screen, and obviously with correct
exposure for the whole.

The scheme is only given here in six gradations of tone. As a matter of
fact, a good autotype has at least from six to eight times the number
of tones, as with a sharp screen and an original cleanly {72} and
sharply drawn in many tones, the light reflects the least alteration of
tone in the size of the grain.

  [Illustration: Fig. 8.]

As previously mentioned, the smallest points represent the highest
lights of the drawing; the larger, according to our graphic
representation, the darker tones, but a correct reproduction of the
grain.

In a similar way obviously the formation of the lines on the negative
behave with an interposed but not revolved screen. Here also the lines
in the high lights of the negative appear more covered than in the
shadows.

The proportion of grain can, if the original requires it, be so
far altered by not giving equal exposures for each position of the
screen—for instance, in the proportion of two to one or three to one.
We obtain then on the given scheme less closed tone gradations, 3, 4,
and 5, and just before 3, and between and after 5, tone gradations, no
single black and white points, but more or less jagged black or white
lines, whilst the open black grain in 1 and 2 becomes more an oval
instead of the round form in 6, and beyond the round openings are drawn
out into ovals.

We have, however, in autotypy still the physical law, which is very
useful to us, and that is the greater or less distance of the point
from the light surface. The nearer a point or a figure is brought to
the wall on which it should throw the shadow, the greater the size
of the original, and so much sharper will be the outlines of the
shadows. The more the point or the figure is {73} removed from the
wall the less the shadow will correspond to the shape of the original;
it will be smaller and less defined. The shape will also frequently
change, and a square will become a round. We have then in the near or
distant position of the lineature to the sensitive plate, on which
it throws its shadow, an important assistance to act on the general
tone gradations of the image. Let us remember that in focussing the
shadow-forming object on to the surface on which the light falls, we
obtain the same formed in all its actuality on the receiving surface;
therefore, when this refers to a lineature with equal proportions of
black and white, we obtain these in equal ratio. When, however, we
remove the lineature from the light-receiving surface, the shadows
which it throws contract, the lights predominate, we obtain no longer
the ratio of 1 : 1 between light and shadow, but about 1·5 : 1 and so
on.

By placing the lineature close to the sensitive plate, we obtain more
closed tones, and as this gradation of tone is carried naturally
throughout the whole of the image, also less high lights, less deep,
middle shadows, whilst the deep shadows appear in their natural
strength. With the removal of the lineature from the sensitive plate,
on the other hand, the ratio of tones for the whole image, as well as
for the details, is displaced. In the first place we shall obtain a
picture which contains more contrasts of black and white. The light
tones become considerably lighter by the reduction of the shadows. The
dark parts, on the other hand, attain full vigour. In the first place,
therefore, the original has to be considered as regards the distance
of the lineature from the sensitive plate. Obviously, therefore, no
accurate directions can be given in a case where feeling and experience
are required. Next to the original, the number of the lines on the
screen has to be considered. As a rule, one uses lineatures with five
or six transparent and opaque lines to the millimetre (= 125–150 to the
inch), and for these a distance of ½ to 1 mm. (= 1⁠/⁠50–1⁠/⁠25th inch)
from the sensitive plate is generally sufficient for most cases. With a
less number of lines the distance can be increased.

Autotypy is a process in which unprintable half-tones can be broken
up by the use of a well-defined physical law into a mathematically
determined grain, and the size of the grain can also be regulated to a
certain extent with certain precautions.

It is, therefore, easily understood that the autotypic process is now
very general and most used, and not only in the limited department of
photo-lithography, but in a more extended way, does excellent service
for the preparation of illustrations of all kinds, for the simplest
picture for the daily paper as for the finely-printed magazines and
journals, for simple monochromatic printing, and for the highest colour
printing.

With accurate knowledge and command of the technique of {74}
photography and lithography, there is required before everything,
for successful work, a faultless screen plate. The indispensable
requirements which must be found in the screen are absolutely opaque
black lines and bare glass in the white lines. The home preparation
of such a screen plate is a somewhat difficult matter, and will not
be absolutely successful if one has not a faultless ruling machine, a
composition which is thoroughly opaque, which adheres well to the glass
and gives clean, sharp lines in ruling, and which does not chip, and
it will require a tremendous expenditure of patience and perseverance.
Glass screens of excellent quality may now be obtained commercially.

For reproduction of the very highest quality, a drawn and etched screen
plate is more suitable than one merely ruled on pigment, which never
gives such sharp results.

From various firms etched screen plates may now be obtained either as
single or crossed-line screens, which fulfil all requirements.

The best screen to use is one with five or six opaque and transparent
lines to the millimetre, which corresponds with 2,500 to 3,600 points
to the square centimetre. The above number of lines will suffice for
nearly all work, and such screens give reproductions in which the grain
is no longer visible to the naked eye, but appears as a closed tone. It
is not advisable to go beyond this number of lines, except in special
cases, when the details of the drawing in the original are specially
small. With a smaller number of about three or four lines to the
millimetre, too coarse a grain results, of which the individual points
become too plainly visible, and these are distracting and act roughly,
and do not accurately reproduce the gradation of tone.

The best proportion between opacity and transparency is 1 : 1. From
this is obtained, according to my opinion, the most beautiful and
restful tones. It must also be remembered that the opaque spots
actually lose considerably in strength in the brighter portions of the
picture by the spreading action of the light.

The printing may be done on bichromated gelatine paper, with which,
however, extremely accurate inking up of the print is essential, and
the prints must not have too much ink and must be very carefully
printed. If, however, very good, clear negatives are used, either of
the direct printing methods, as already described in Chapter IV., is to
be preferred. (See No. 4 Supplement.)


2. PHOTO-LITHOGRAPHIC PROCESSES IN WHICH THE GRAIN IS NOT FORMED DURING
THE EXPOSURE.

Of the many existing processes by which the breaking-up of the
half-tones into printable lines or grain is effected, not in the
negative, but subsequently by mechanical and chemical action on the
stone or plate or the transfer film, I will only mention those {75}
which appear to me to be the most important, the new methods which
have already found firm footing in practical work or which appear
likely to do so. All the older processes, which were either never
actually successful or have been superseded on account of difficulty of
working, we may properly pass over.


(A.) THE PATENT ASPHALT PROCESS OF ORELL, FÜSSLI, AND CO. USED FOR THE
PREPARATION OF COLOUR PRINTS.

I have already mentioned that the use of light sensitive asphalt for
the preparation of printing plates for the various branches is by no
means new.

The fundamental principles of the well-known processes we find also
used in the process of Orell, Füssli, and Co.

The grained stone is coated with a thin film of light-sensitive
asphalt, the composition of which we have previously learnt, and
exposed under a reversed or stripped negative. The image after correct
exposure is developed, and then, according to the construction of
the asphalt, in combination with the graining of the stone and the
developer, there is formed a finer or coarser grain, or a closed or
open image.

The development is effected with petroleum, to which one-fifth or
one-sixth of its volume of benzine is added, or with turpentine alone.
Development takes place rather rapidly, and after a short time the
image appears on the stone. The print is then treated as was suggested
in asphalt printing; the stone is first gummed, and then by rolling
up with ink and etching rendered suitable for printing. The pictures
produced by this have a very fine grain and are in appearance very much
like good collotypes; still two or more tones are necessary to obtain
an absolutely closed and vigorous action.

Very similar to Orel and Füssli’s process is the following, also
patented.


(B.) THE COLOUR PRINTING PROCESS OF WEZEL AND NAUMANN OF REUDNITZ,
LEIPZIG.

In this process also all the colour stones of a chromo picture are
produced from a single stripped and reversed negative which is taken
of the original. For the preparation of any colour stone there are
three distinct stages. The first stage is the exposure, the second the
development, and the third the development continued still further,
and any necessary small help by the lithographer. In each stage a
special mode of treatment is required, according to whether the stone
in question is to be used for a light, a more vigorous, or full colour.
The stones for grey and the light blue or light red inks—thus those for
many surfaces, but with few details—are treated differently to those
for yellow, the second red {76} or blue; and these, again, differently
to those for brown or quite dark colours.

Everyone only slightly conversant with colour printing knows that
the first plates are used for the general tones of the picture, and
contain, therefore, few details, and with the exception of the highest
lights are tolerably full; the latter plates, on the other hand, which
are devoted to the darker colours, contain less toned surfaces, but,
on the contrary, more details of the drawings. In order to attain this
correctly the three stages of the production of the plates are carried
out with this end in view.

It should still be mentioned that the more or less fine graining of the
stone determines the general ratio of the grain of the picture.

The first stage is the exposure of grained stone coated with asphalt.
With longer or shorter exposure it is possible to make the asphalt film
more or less soluble, that is to say, to make the same more or less
capable of resisting ethereal oils.

It is therefore possible at this stage, by long exposure of the asphalt
film, to give to the colour stone for bright colours more tone and less
details. The stones for the darker inks are printed for a shorter time,
and the asphalt film is less capable of withstanding the solvents, and
the resulting plate contains less tones and more details. Finally, the
plates for the deep colours are normally printed; the asphalt film is
still less resistant, and consequently the stone will only have tone
and details on those places which in printing ought to be the darkest.

It is possible, therefore, by correct manipulation of this operation,
to obtain approximately the correct colour plate.

There is, however, in the second process a corrector for the first. The
development may be so performed that by the longer or shorter use of
strong solvents, Hungarian or Russian turpentine, more or less of the
asphalt will be dissolved. Thus if a slight error is made in printing
it can be made good in developing. As a rule, the stones for bright
colours, which consist of many tones, are not developed so long as
those for the stronger colours. The actual stones for the deep colours
are very strongly developed, so that almost all the delicate parts of
the picture disappear, and only the dense strong parts remain on the
stone.

Still the fine details which are to be found in the vigorous parts, and
which cannot be recognized, must be brought out. The fine parts of the
drawing must be quite clear if the details are to be recognized, or the
picture will be a fuzzy copy of the original, wanting in structure.

This fault is remedied in the third stage of the treatment, in which a
strong development of the picture is effected with strong acting oils
or benzole and turpentine. As this operation, however, would also wash
away such delicate places which ought to remain on the colour stone,
they must be covered with solution of gum and allowed to dry. Then
those parts not covered with gum, {77} in which the details of the
image cannot be seen, are painted for a longer or shorter time, as may
be required, with a brush dipped in the developing solution, and when
correctly developed may be covered up. The lighter places are treated
for a shorter time, the very dark places for a longer time.

By this treatment the particular parts of the picture become lighter
and lighter, the details appear more and more; and, finally, the whole
picture shows as it should do. Then the gum is washed off and the
stone subjected to the already described treatment, so as to make it
suitable for printing in quantities. Finally, the lithographer can make
corrections with a needle or tusch.

This process may be used, therefore, to prepare colour-printing plates
from a negative obtained in the camera from an oil painting or any
coloured original.

The negative for this process must contain all the details very clear,
must be soft, and not be too dense.

The different colour plates are thus in this process obtained by long
or short printing, by strong or weak developing, and finally the
details in the dark plates are obtained by separate development and
covering up the other places with gum.

The breaking up of the half-tones into printable grain is effected by
graining the stone, before coating with the light sensitive asphalt
film. On the finer or coarser graining of the stone depends also the
structure of the grain of the image.

This process yields the most beautiful results with correct
manipulation, and in the hands of an expert photographer and
lithographer is a valuable aid to the preparation of colour plates. The
process is patented.


(C.) J. BARTÖS’ PROCESS FOR PREPARING PHOTO-LITHOGRAPHS AND PHOTOTYPES
IN GRAIN AND HALF-TONE.

Bartös’ process belongs to those in which the breaking up of the
half-tones into a printable grain is effected subsequently on the plate
or stone by mechanical means. This is attained in a very original
manner by means of a sandblast, which makes the half-tone printable.
We have here not the breaking up of the half-tones in a mathematically
regular manner, dependent on optical laws, as is the case with
autotypy, but a method similar to that of Pretsch, which obtains the
printable grain by reticulation of the chromated gelatine film, or
other discoverers who attain the same result by asphalt dusting or some
other means.

For this process a well-polished litho stone or zinc plate is coated
with a thin film of varnish, composed of—

 Chloroform      300 g.
 Mastic            5 g.
 Asphalt          10 g.
 Benzole         300 g.
 Linseed oil       2 g.

{78}

On the stone or plate thus prepared is transferred a carbon image in
half-tone.

This pigment film, when completely dry, is flowed over with a mixture
of—

 Glycerine      35 g.
 Water          25 g.
 Alum            2 g.

and this should be allowed to act for about five minutes and then
removed with blotting-paper. After this operation the pigment image can
be easily destroyed. The pigment image is now exposed to the action
of a weak sandblast. The sand acts on the relief image and gradually
destroys it, and so that the film of varnish underneath is gradually
grained.

After the pigment film has been removed the picture shows in all its
details in grain on the varnish of the stone or plate. The image is now
visible on the film of varnish, according to the strength of the tones
in partial graining, and can be etched into the stone or plate.

This is effected by etching with phosphoric acid—

 Water              100 g.
 Phosphoric acid      4 g.

When the etching solution has acted for about two minutes, the stone is
washed and coated with a solution of gum—

 Water              100 g.
 Gum arabic           5 g.

and allowed to dry.

Then the film of varnish is removed with a pad of cotton wool damped
with turpentine, the dry stone rolled up with litho ink, damped, and
the excess of ink rolled off. The picture now shows with all its finest
details on the stone, and can be printed.

In preparing a relief printing plate the film of varnish forms the
resist for the first etching. It is then rolled up and etched in the
usual way.

For preparing larger pictures on stone or metal plates, in which the
grain must be coarser than with small pictures, the fully-developed and
still damp pigment image is dusted with powdered resin and the film
allowed to dry with the powder adhering to it. The pigment image thus
dusted is treated, as previously described, with alum and glycerine,
exposed to the action of the sandblast, and then etched with phosphoric
or nitric acid.

As the soft pigment film receives a grain by the dusting, this is
reproduced of the same size by the action of the sandblast on the film
of varnish on the stone or plate.

The principal points of this process of preparing photo-lithographs or
phototypes in half-tone, with a grain, are as follows:—

1. From the photographic negative a pigment image is taken {79} and
transferred to a litho stone or zinc plate, which has been previously
coated with varnish.

2. The pigment image is then exposed to the action of the sandblast; and

3. Then the pigment image is removed, and the image obtained on the
film of varnish is etched.

In the K.K. Hof und Staatsdruckerei photo-lithographs as well as
phototypes have been prepared with excellent results by this process.
The former in result are similar to the productions of the Orell and
Füssli process, and the latter were noticeable for good gradation.
On the other hand, it cannot be denied that this process, which is
patented, has been already surpassed by autotypy, which is far simpler
and easier to work, and is founded on a scientific basis.


(D.) LITHO-HELIOGRAVURE.

This process, invented by Chas. Eckstein, of Hague, the general
director of the Topographical Bureau of the Royal Netherland General
Staff, also belongs to those processes of photo-lithography by means
of which any picture in half-tone can be reproduced. The breaking up
of the half-tones is effected, as with the autotypic methods, by the
use of a lineature, but instead of this being done in the photographic
exposure, it is effected direct on the stone before the transfer of
the photographic image. In this particular process the stone itself
is not coated with a light sensitive film and printed on direct, but
the ruling is made on the stone, and then a negative pigment image—a
diapositive—is transferred to it exactly the same as with photogravure
on copper. A further feature is that the result is not an ordinary
transfer stone result, but an intaglio etched stone, which is printed
from the depressions.

For this original process the basis is a ruled pattern stone, prepared
with great care and accuracy. For preparing this a grey stone of
the best quality should be taken, and one without any chalky spots,
crystals, or holes. This should be polished with a coarse cloth
and oxalic acid solution till it has a very high polish. On the
highly-polished stone surface is spread a very thin but even film of
asphalt.

The solution is composed of—

 Asphalt       5 parts.
 White wax     6 parts.
 Stearic acid  6 parts.

This mixture is boiled, and to it whilst boiling is added in drops a
solution of two parts of soda. When cold this mixture, which is fairly
hard, is dissolved in about an equal volume of turpentine, filtered and
kept in bottles for use.

A sufficient quantity of this asphalt solution, which must not be
sensitive to light, is poured into the middle of a levelled stone and
{80} distributed by means of a lithographic ink roller, which must not
be used for any other purpose but this, till the coating is absolutely
even and shows a light brown colour.

When this film has become quite hard, fine parallel lines are drawn
over the whole surface of the stone with a very accurate working ruling
machine, by means of which from five to ten lines per millimetre can be
ruled.

When the ruling is finished the stone is given a margin of wax, and
quickly and evenly flooded with the following etching fluid—

 Pure nitric acid       0·16 parts.
 Alcohol 36 per cent.   0·60 parts.
 Water                 35 parts.

And, watch in hand, is etched for about half-a-minute.

Instead of the above a solution of—

 Glacial acetic acid    2 g.
 Water                100 g.

may be used and allowed to act for half-a-minute. The stone is then
well washed under a strong stream of water, allowed to dry, and covered
with linseed oil. After about five minutes the whole of the stone may
be washed with turpentine. Then it should be inked up with a pad, care
being taken that all lines take the ink well and evenly. This pattern
stone serves as the original plate for the subsequent ruled transfer.

From the original ruled stone can be made, according to the nature of
the original, a single, double, triple, or four-fold transfer.

For preparing a stone with a ruled transfer, a smoothly ground stone
well polished with oxalic acid is evenly coated with sensitive asphalt
solution. On this, when dry, the desired single or crossed transfer
from the original stone is made, and dusted with bronze powder. This
adheres to the lines of the pattern, and in combination with the
printing ink protects the asphalt film underneath from the action
of light. During the subsequent exposure, which, according to the
sensitiveness of the asphalt and intensity of the light, can last from
a half to two hours or more, the particles of asphalt not covered by
the bronze powder become insoluble, whilst the protected parts preserve
their solubility.

After correct exposure the surface of the stone is carefully washed
with a tuft of cotton wool soaked in oil of turpentine, when the
particles of asphalt underlying the bronzed lines dissolve. The stone
at these parts is laid quite bare, and therefore made capable of being
subsequently etched. The deep etching of the pattern is effected in
the same way as was suggested in the preparation of the mother pattern
stone.

By this method a positive pattern is obtained, that is to say, the
lines print, and the impression shows therefore a black network.

A second method of making a pattern transfer consists in making a
pull from the original stone on to chalk transfer paper. {81} This
pull is then damped on the back, and when just properly damp is laid
on the polished stone (without any asphalt) and the transfer made.
In order to remove the chalk paper without damaging the pattern the
stone is covered with warm water, when the lines will dissolve. The
simple pattern will now be found on the stone, which should now be well
washed, then dusted with resin powder, which should be melted on with
ether vapour. Then if the direction of the first lines was vertical,
the second transfer is arranged with the direction of the lines
horizontal to the first, and there is thus obtained a simple crossed
pattern. With four-fold crossed patterns the subsequent pulls are made
in opposite diagonal directions. After each transfer the stone is well
washed, allowed to dry, then dusted with resin powder, and with ether
melted on to the pattern.

The stone is now deep etched with dilute nitric or acetic acid and
covered with linseed oil.

By this method a grain instead of lines is obtained. By polishing the
stone and transferring on to it, as well as by etching the places not
covered by the ink, we have the pattern reversed, that is to say, it is
converted into grain.

For further operations of litho-heliogravure a very clear and soft
negative is required, from which a glass transparency is taken. Under
this transparency pigment paper sensitized on a 20 per cent. solution
of potassium bichromate is printed to 8 or 10 degrees Vogel. Printing
must be very carefully performed, as with under-printing too many
details are lost. The exposed pigmented paper is washed in cold water,
laid film side down on the previously prepared stone, and pressed into
contact with an india-rubber squeegee. It should then be allowed to dry
in a not too dry or too warm place.

The stone should now be placed in a trough with warm water of about
40 to 45° C., and care should be taken to obtain water of as even a
temperature as possible. After about five minutes the paper will be
free from the stone, which should remain in the bath and be developed
so long by shaking in order that the water may flow evenly over it till
the image appears quite distinct; a negative image is thus obtained on
the stone. The film is then allowed to dry spontaneously for four or
five hours till the pigment image has become quite hard.

For etching a solution of perchloride of iron of various strengths is
used, 40, 37, 33, and 30° Beaumé. With subjects very rich in tones
all four will be used; with simpler subjects one or the other may be
omitted.

The etching will begin, as a rule, with the 40° solution. The ferric
chloride will first dissolve the thin, hardened pigment film and then
go through the open lines of the pattern, where it will attack the
stone and etch the deepest parts.

Slowly the ferric chloride dissolves also the thicker pigment {82}
film—begins also to etch the stone there, but less deeply. To tell
when the four solutions should be used in turn, as well as the correct
moment to interrupt the etching, requires considerable experience. The
30° solution, the weakest of the ferric chloride solutions, is used
last, and in consequence of the greater proportion of water possesses
a solvent power for the whole of the light-hardened pigment film.
Accurate directions as to how long the etching with the different
solutions is to be continued cannot be given, as this depends upon the
character of the subject as well as upon the thickness of the pigment
image. It may be always assumed, however, that any individual etching
ought to last under no circumstances longer than three to four minutes.
With well-covered stones the first etching should not be allowed to act
so long as the last, and _vice-versâ_ with less covered stones.

As soon as the image shows the correct character through the etching
solution the stone should be brought under the tap in the trough and
quickly washed with clean cold water. The surface of the image should
then be flowed over with oil of turpentine in order to remove the
asphalt and gelatine film, and finally well washed with the rose and
allowed to dry. The picture will be found deeply etched into the stone.
The stone is now smeared over with linseed oil, inked up, and further
treated as in ordinary lithogravure.

In this process the negative pigment image is transferred to the stone
and the printing image prepared by etching; the formation of the grain
is produced by the pattern printed either on a polished stone, when
it is converted into points, or the transfer may be effected on to an
asphalted polished stone, when a network of lines will be obtained.

For dark subjects the latter process is better, for lighter subjects
the grain.

Printing from such a plate has more similarities with etching printing
than from stone; the effect of the ink is very good and expressive.

Various pictures executed by Eckstein and in our establishment in one
or more colours have proved the value of this process in practice.

The foregoing are the different photo-lithographic methods for
obtaining printing images in half-tone, and although in no way
exhaustive, yet it appears to me that they are practically the most
important.

{83}




APPENDIX.


1. NEGATIVE TRANSFER WITH BICHROMATED GELATINE PAPER.

The properties of bichromated gelatine paper can also be very well
used for the so-called negative printing, and this method offers many
advantages.

In order to convert a positive printing image into a negative various
methods may be used; the most convenient for the lithographer is the
following:—A good litho stone is first ground in the ordinary way and
then the surface rubbed with a pad and oxalic acid solution till it
has a high glaze or polish. On to this stone is then transferred a
sharp impression in a non-greasy ink from the positive printing image.
According to the destination of the stone for large or small editions
one of two processes may be adopted. If a thousand or more pulls are
required from the stone the transfer may be dusted with resin powder,
and this melted with the burning, heating, or ether process and the
drawing etched in relief with 8 to 12° nitric acid and gum. Then the
stone may be well washed with water and the acid removed with one to
two per cent. acetic acid.

For small runs the first etching is omitted, and the stone treated with
acetic acid. In both cases the stone should be well washed, dried, and
then coated with dissolved lithographic tusch or autographic ink. The
greasy substances of these materials penetrate into the surfaces of the
stone that are laid bare, and firmly adhere. When the tusch or ink is
completely dry the stone is washed with turpentine, inked up, and one
now has a negative image from the subject in question, which shows all
the original printing places in white and all white places black.

The process of preparing such negative prints by the use of bichromated
gelatine papers is much simpler.

A sheet of gelatinized paper is sensitized for this purpose on a 5 per
cent. bath of potassium bichromate, squeegeed to a sheet of plate-glass
and well dried, and on this is made with black ink, which is very
opaque, in the dark or in gaslight, a sharp clean print. This print
is then laid on a flat cable, under a sheet of plate-glass, so that
it cannot roll up, and exposed to the light for from five to thirty
minutes. A long exposure rarely does harm in such cases, as the good
opaque black ink allows no rays of light to pass through to those
places which later should print white.

The next manipulation is the development and inking up, which is
done as in ordinary photo-lithography. In this operation all {84}
those places which were not covered up by the printing will take the
developing ink; on the other hand, those places where the impression
was will wash out clean and white. The print has assumed the appearance
of a photographic positive. The print is now treated like any other
photo-lithographic print, and finally transferred to a stone or zinc
plate. This method is distinguished by its simplicity and safety;
it has also the advantage that any desired printing subject can be
directly transferred in negative form to a zinc plate for relief
etching, which otherwise could only be done by preliminary transfer to
stone and subsequent transfer to zinc.


2. PHOTO-AUTOGRAPHY.

DRAWING WITH AUTOGRAPHIC INK OR LITHOGRAPHIC CHALK ON A CYANOTYPE,
SALTED OR OTHER PRINT FROM A PHOTOGRAPHIC NEGATIVE OR POSITIVE.

By autography we understand that method of reproduction by which any
writing or drawing is made on a prepared or not prepared paper with
greasy ink, tusch or chalk, which is subsequently transferred to stone
or zinc for printing, or to zinc plates for relief etching.

Autographic drawing papers differ for the different purposes, and for
writing and simple line drawings smooth hard post paper is used, and
lined transfer paper for fine pen or chalk drawings. The latter are
prepared commercially by Angerer and Göschl. Very beautiful grained
drawings can also be made for transfer on pyramidal grain paper. The
proof for such drawings is usually done with lead pencil or red chalk,
or it may also be made on a gelatine proof.

In order to obtain fully and completely the character and correct
reproduction of the drawing, without special expense of artistic help,
it is advisable to use a photographic print as proof. It should be
noted that for pen drawing on smooth paper with greasy tusch or ink,
for chalk drawings on a prepared grained paper done as previously
mentioned, with greasy lithographic chalk, the drawing should be
transferred direct to zinc or stone in order to save having to make
subsequently a photographic print.

If a pencil, red crayon, or other proof is used for an autographic
drawing on paper with the idea of transferring it direct to stone or
zinc, a suitable photographic print may also be used on suitable paper
without any disadvantages.

For the prints all photographic papers without glaze, such as ordinary
plain salted paper, Eastman’s positive bromide paper, and others, may
generally be used. Glossy or albumenized papers are not suitable for
this, as the ink runs, and does not form solid clean lines. {85}

The best of all, however, is cyanotype paper, as even with very deep
printing it keeps the details in the shadows open, and on account of
its blue tones is more suitable for the subsequent drawing with black
tusch. When, however, prussiate paper is not handy, and subjects with
fewer shadows and less details are to be treated, any of the other
papers above-mentioned may be used.

If ferro-prussiate paper is to be used, the same may be prepared as
recommended on p. 23.

The so-called salted or plain paper is prepared as follows:—A sheet of
well-sized post paper is first bathed in a solution of—

 Ordinary salt   1 part
 Water          25 parts

and then sensitized in a solution of silver nitrate 1 : 12. It is
printed till the print has assumed a fairly full brown tone, and all
the details in the shadows are well printed out. It should then be
toned in the following toning bath:—

 Distilled water                      1000 g.
 Sodium acetate (twice fused)           15 g.
 Solution of gold chloride (1 : 100)    25 g.

till the print has assumed a deep dark brown tone. It should then
be fixed in a solution of sodium hyposulphite, 1 : 15. It should be
printed rather deep, as in toning and fixing the image loses in depth.
It is moreover unnecessary in this case to make a beautiful print; the
chief thing is only that all details of the image should be clearly
seen. The print is then well washed in frequent changes of water and
then dried.

The print on Eastman’s bromide paper is prepared as follows:—

Red light must be used. It should be printed by an ordinary gas flame
at a distance of about 50–80 cm. (= 24 to 36 ins.) for 1 to 20 seconds,
according to the density of the negative. Here again a technically
perfect print need not be arrived at, but one which contains all the
details very clear. Under a good transparent negative a useful image
for the artist will be obtained with about two seconds’ exposure.

The developer is composed of two solutions:—

 (A.) Water                       500 g.
      Neutral oxalate of potash   165 g.
 (B.) Water                        50 cm.
      Sulphate of iron             15 cm.
      Concentrated sulphuric acid   2 drops
      Or glacial acetic acid        5 drops

Three parts of solution A and one part of solution B should be {86}
mixed together. As soon as the shadows have attained the desired tone,
the prints should be placed in several fresh baths of

 Water           200 ccm.
 Acetic acid       1 drachm.
 Sat. sol. alum   50 g.

and then washed and fixed in a bath of

 Water                50 ccm.
 Sodium hyposulphite  10 g.

for about ten minutes. Then well washed and dried.

For pen drawings all not gelatinized or albumenized printing papers
may be used as already mentioned. The chief thing is that the paper
should be well-sized and of good firm texture. If prepared grain paper
is used, which is provided with a film of chalk, kaolin, or any other
white colouring matter combined with gelatine, and on which film the
grain is impressed, only prussiate prints can be used. The paper is
sensitized as previously described, only it is advisable not to leave
it too long in the solutions, or else the film may become softened. The
film will also dissolve in hot water at about 80° C.

The prints as soon as dry can be used for drawing on. On the grain
papers the outline may be drawn with the pen and be shaded with chalk,
or it may be drawn with chalk only. With unprepared papers it is
advisable to coat them with a thin solution of boiled starch, as then
the transfer to zinc or stone is most exact. The drawing may also be
left a long time without spoiling. The coating is performed with a pad
dipped into the liquid, which consists of one part of fine bookbinder’s
starch and four or five parts of water, and passed several times over
the print.

The drawings ought only to be done with greasy lithographic tusch
or chalk or autographic ink, which consists principally of greasy
materials and lampblack. For pen drawings hard pens should be used, and
care must be taken to make thick strokes. Only a little tusch or ink
ought to be taken into the pen, so that it does not run out, and thus
clean, sharp lines be obtained. If this be observed very close shadings
and cross lines can be produced clean and neat.

When the drawing is finished and the tusch or ink has become dry the
same should be laid between damp blotting-paper, and meanwhile a clean
ground, and dry pumiced stone worked in the press and the pressure
correctly adjusted. As soon as the drawing has become moderately damp
right through, and the paper feels soft without being wet, it should
be laid with the image downwards on the stone and transferred to the
same with strong pressure. After repeated working the paper will
adhere firmly to the stone. In order to loosen it the stone should be
covered with hot water of about 80° C., when the film will dissolve and
the paper become quite free. Any exertion of force must in this {87}
operation be quite avoided, and the paper must not be pulled off with
violence. All, even the finest lines, will have been transferred to the
stone. The stone is now gummed, if possible allowed to stand for some
hours, and then etched with a gum etching solution of two degrees’ acid
strength, or later etched in relief, and is ready for printing. If the
transfer is made to zinc, for printing from this the plate is treated
as suggested on p. 6. If, however, a relief etching for the typographic
press is to be prepared of the subject, the transfer is made on to a
smooth polished zinc plate.


3. LITHOGRAVURE.

With this particular process an intaglio printing stone or intaglio
printing plate is prepared by chemico-physical means.

This process was discovered and brought to great perfection by Chas.
Eckstein, the general director of the Typographical Bureau at the
Hague, and offers especially many advantages for the reproduction of
maps.

A map engraved, drawn, or transferred on stone, or written in
on copper, in originally one colour, can by this process in a
comparatively easy way be converted into a many-coloured print; this
process can also be used very advantageously for changing the names for
the places—rivers, mountains, etc. In the first place intaglio original
printing plates in all the colours can be prepared which can then be
printed for further reproduction; in the second case it is necessary to
re-engrave the network, hydrography, etc.

When it is desired to convert a monochrome image into a multi-coloured
map, as many stones as there are colours to be used must be first
ground and polished with oxalic acid till they have a high polish.

In the meantime an asphalt or other light-sensitive solution should be
prepared, with which the stone is coated in the dark very evenly, and
somewhat more than is done for a photo-lithographic print.

The asphalt solution is composed of—

 Syrian asphalt    20 g.
 Chloroform       300 g.
 Benzole          100 g.
 Oil of lavender   20 drops.

After it has been dried in the dark the impression from the black
plate, which should be previously made on transfer paper, is
transferred to the asphalt film as previously laid down, and before it
is dry dusted with bronze powder. All lines, titles, or figures which
should not appear on that particular colour-plate must be then covered
with the above asphalt solution, and only those places, for example,
on the one plate all titles, on another all the roads, on a third the
river courses, and so on, should be left, all of which later should
appear in printing. {88}

The stone is now, according to the sensitiveness of the film and the
strength of the light, exposed for from fifteen minutes to two hours.
Over-printing, if it is not very exorbitant, does not do any harm
with the stronger letters or lines on account of the good covering.
With very fine lines, however, more care must be taken. If there is
any doubt as to the length of the exposure a test may be made at one
corner of the plate with a pad dipped in rectified turpentine. When the
asphalt will no longer dissolve the exposure may be discontinued. With
some experience the photometer may also be used.

Then the whole surface should be washed with rectified turpentine and a
pad of cotton wool, when the ink lying under the bronze, that is, the
lines where the asphalt has been protected from the action of light
dissolve, and the surface of the stone appears. The rest of the asphalt
film has become insoluble from the action of light, and now forms the
etching-ground for the reversed negative image on the surface of the
stone.

When the stone has been well washed with water it may be etched, which
is done with glacial acetic acid two parts, water 100. When there are
any fine lines in the drawing the etching is interrupted at the end
of two minutes, and they should then be covered with tusch, and then
when the tusch is dry the other parts are further etched for a longer
or shorter time according to the degree of fineness. In any case the
time of etching should not exceed five minutes. The stone is allowed
to dry and then coated with a solution of tusch or linseed oil, which
penetrates into the etched parts and makes them capable of taking
ink. After about ten minutes the whole stone should be washed with
turpentine or benzole, by which the etching ground is removed, when the
stone is inked up like an ordinary gravure.

In this way is obtained a stone with deep etched drawing, which
according to the blocking contains the titles, the rivers or roadways,
and from which subsequently the necessary gravures can be taken. This
stone can either be used for direct printing or it may be used as an
original stone from which the necessary transfer can be made.

The same process may also be made for intaglio printing plates on zinc
or copper, only then the etching must be done with nitric acid or
ferric chloride.

Instead of the transfer on the light sensitive film, a drawing on
transparent paper may be used, or a photographic transparency. The
exposure in this case, as the opaque ink and bronze powder are not
used, must be very carefully estimated.

The advantage of this process is that an intaglio printing surface may
be obtained so that engraving is entirely or partially avoided, and
that this printing surface may be used as an original from which the
reproductions are made.

{89}


SCRAPER BOARDS, MANUFACTURED BY AUGERER & GÖSCHL, VIENNA.

No. 6.—A white scraper board printed with black lines. There are 40
black and 40 white lines to the centimetre; the ratio of black to white
is as 1 : 2. At right angles to the black lines impressed lines are
arranged, of which 37 are depressed and 37 raised up to the square
centimetre.

No. 7.—This is practically the same as No. 6, only that the lines are
slightly less in number, namely, 35 black and 35 white and 26 impressed
lines in equal areas to No. 6.

No. 8.—This contains dots instead of lines, both black and impressed;
there are 1,156 black dots at regular intervals, and 961 impressed dots
to the square centimetre.

No. 9 is a smooth scraper board.

Nos. 10 and 11.—These are impressed with straight lines in the
proportion of 1 : 1. With No. 10 there are 27 lines, in No. 11, 37 lines
to the centimetre.

Nos. 12 and 13.—These are impressed with lines at right angles to one
another, so that regular squares are formed. No. 11 contains 730, No.
12, 1,370 squares in every square centimetre.

  [Illustration]




INDEX.


Acid, Acetic, 10

― Citric, 10

― Gallic, 10

― Hydrochloric, 9

― Nitric, 9

― Oxalic, 10

― Phosphoric, 10

― Sulphuric, 9

Action of Lineature, 69

Albert’s Photo-litho Paper, 56

Albumen Process, 64

Angerer & Göschl, 25

Asphalt, 17

― Process, 60

― ― Husnik’s, 60

― ― Valenta’s, 61

Autographic Ink, 7

Autotypy, 67

― Negative, 41


Bartös’ Process, 20, 77

Behaviour of Asphalt on Stone, 8


Cadmium Intensification, 40

Chromate Salts, 48

Coating the Stone, 62

Cold Melting Process, 12

Correcting Negatives, 35

Cyanotype Paper, 24

― ― Bleaching, 24


Dark Room, The, 34

Deep-etching Process, 11

Developer, 37

Developing Ink, 8

Direct Printing, 60

― Transfer, 15

Distance of Lineature, 73

Drawing on Blue Prints, 23

― ― Prepared Paper, 25


Eberle’s Process, 11

Eckstein’s Process, 20

Electric Lamps, 31

Etching the Stone, 10


Failures in Transfers, 58

Fixing, 38

Fox Talbot, 17

Franz’s Paper, 55


Galls, Tincture of, 10

Gelatinizing Paper, 47

General Notes on Photo-lithography, 49

Gold and Mercury Intensifier, 38

Greasy Drawing Materials, 6

Gum Arabic, 10


Half-tone, Breaking up, 20

― Photo-lithography, 67

Hebensperger’s Process, 66

Hübl’s Hydroquinone Intensifier, 38


― Iso Emulsion, 43

Husnik’s Asphalt, 17

― Photo-litho Paper, 53

Hydroquinone Developer, 42


Indirect Transfer, 16

Inking up and Developing, 51

Intensification, 37

Intensifier, Lead, 40

― Mercury, 40

― Metol, 39

― Silver, 40

― Uranium, 40

Iodized Collodion, 37

Isochromatic Emulsion, Albert, 41

― ― Hubl, 43


Lemercier and Lerebours, 16

Line Drawings, 21

Litho Chalk, Hard, 7

― ― Soft, 8

― Stone, 4

Lithogravure, 87

Litho-Heliogravure, 79

Lithography, Theory of, 3


Making Direct Negatives, 36

Mungo, Ponton, 17


Negative for Photo-litho, 34

― Transfer with Paper, 83

Negré, 17

Nicephore, Niépce, 16


Orell and Füssli Process, 20, 75


Photo-Autography, 84

Photo-Litho Transfer, 57

Photometer, 51

Poitevin, 17

Prism, 44

Printing, 62

― on Bichromated Gelatine, 50

Pyramidal Grain Paper, 26


Reproduction of Prints, 27

― Size of, 28

Reversed Negatives, 44


Sacher’s Fish-glue Process, 66

Scamoni’s Process, 12

Scraper Boards, 25

― ― Schäuffelen & Co., 26

Sensitizing Paper, 49

Silver Bath, 37

Stripping Negatives, 45

Studio, The, 30


Tusch, 7


Valenta’s Asphalt, 17


Waterhouse’s Arrowroot Process, 66

Wezel & Naumann, 75


Zinc Plates, 5

― ― Roughened, 6

― ― Oxidized, 6


  [Illustration]




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AMERICAN, COLONIAL, &C., work is represented by a few typical pictures,
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THE SCIENTIFIC AND PRACTICAL applications of photography are not
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THE EDITION IS LIMITED to 10,000 copies.

Order early. Ready October 20th.

Published for “THE PHOTOGRAM” Ltd.

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TRANSCRIBER’S NOTE

Original spelling and grammar have been generally retained, with
some exceptions noted below. Original printed page numbers are shown
like this: {52}. Original small caps are now uppercase. Italics look
_like this_. Footnotes have been relabeled 1–3, and moved from within
paragraphs to nearby locations between paragraphs. A few missing
full stops were inserted, for example after “avoided” on page 49.
The transcriber produced the cover image and hereby assigns it to
the public domain. Ditto marks have been removed and replaced by
repetitions of the referenced text. Subscripts are indicated by a low
line followed by curly brackets, for example as in K_{2}Cr_{2}O_{7}.
Superscripts look like this: “BENJ^{N.}”. Original page images are
available from archive.org—search for “photolithography00frit”.

There are twenty-four advertisements at the end of the book. A new
heading is added at the beginning of that section. The original book
had the advantages of typography, page-breaks, and illustrations
to distinguish one ad from the next. In this text edition, lacking
those advantages, each ad is enclosed within transcriber’s markup
“[advertisement]” and “[/advertisement]”.

Page 2. “thought than an English translation” to “thought that an
English translation”.

Page 38. In the sentence “If the desired blackening is not effected
with one application the operation must be completed”, it seems likely
that “completed” should be “repeated”.

Page 39. “Gum arabic 17.5” to “Gum arabic 17·5”.

Page 53. “procesess” to “processes”.

Page 56. “tranfers” to “transfers”.

Page 61. “C_{6}H_{3}(CH_{3})3” to “C_{6}H_{3}(CH_{3})_{3}”.

Page 69. “great intensity on the sensitive will” to “great intensity on
the sensitive plate will”.

Page 73. “½ to 1 mm. (= 1⁠/⁠12–1⁠/⁠25th inch)” to “½ to 1 mm.
(= 1⁠/⁠50–1⁠/⁠25th inch)”, though other interpretations are possible.
For example, the similar instance on page 85 “50–80 cm. (= 24 to 36
ins.)” is wrong (or, speaking more charitably, inaccurate), but is
retained as printed.

Page 81. “transfering” to “transferring”.










End of the Project Gutenberg EBook of Photo-Lithography, by Georg Fritz

*** 