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  THE ESSENTIALS OF ILLUSTRATION

  A PRACTICAL GUIDE TO THE REPRODUCTION
  OF DRAWINGS & PHOTOGRAPHS
  FOR THE USE OF SCIENTISTS & OTHERS

  By
  T. G. HILL

  Reader in Vegetable Physiology in the University
  of London, University College

  LONDON
  WILLIAM WESLEY & SON
  28 Essex Street, Strand
  1915


PRINTED BY THE WESTMINSTER PRESS, LONDON, W.




CONTENTS


                                                    PAGE

INTAGLIO PRINTING                                     1

  Intaglio plates                                     2

  Line engraving                                      2

  Etching                                             5

  Soft-ground etching                                 6

  Mezzotint                                           7

  Photogravure                                        8

PLANE SURFACE PRINTING                               15

  Lithography                                        15

  Chromolithography                                  20

  Photolithographic processes                        23

  Collotype                                          23

  The preparation of illustrated pages               26

RELIEF PRINTING                                      33

  Woodcuts and engravings                            33

  The Half-tone process                              37

  The Half-tone three-colour process                 46

  Photomechanical line blocks                        49

  The drawing of microscopic details                 67

  The drawing of diagrams and apparatus              72

  The drawing of maps                                76

  The drawing of graphs or curves                    79

  The swelled gelatine process                       84

The Relative Cost of blocks and plates by
    various processes                                89

LITERATURE                                           95




ILLUSTRATIONS


1. PLATES

PLATE

  1 An original lithograph by Mr. Harry Becker.

  2 Chromolithograph. Messrs. Gerrards, Ltd.

  3-5 Collotype.      Messrs. Andre, Sleigh & Anglo, Ltd.

  6 Half tone.        Swan Electric Engraving Co., Ltd.

  7 Half tone.               \
                             |
  8 Photogravure.            |
                             |
  9 Collotype.               | Messrs. Andre, Sleigh &
                              > Anglo, Ltd.
  10 Half tone.              |
                             |
  11 Half tone.              |
                             |
  12 Half tone three colour. /


2. TEXT FIGURES

  Tailpiece, p. 11. Electrotype from the original wood
                      engraving by Bewick.

  Tailpiece, p. 30. Line block.  Messrs. Bourne & Co.

  Fig. 1.           Wood engraving.
                      Messrs. Edmund Evans, Ltd.

  Fig. 2.           Wood cut.     Mr. G. N. Oliver.

  Figs. 3-6.        Line blocks.
                      Messrs. Andre, Sleigh & Anglo, Ltd.

  Figs. 7 and 8.    Line blocks, reproductions of a wood
                      engraving.   Mr. C. Butterworth.

  Fig. 9.           Line block.

  Figs. 10-13.      Line blocks, reproductions of wood
                      engravings.

  Fig. 14.          Line block.

  Fig. 15.          Line block.
                      Messrs. Andre, Sleigh & Anglo, Ltd.

  Fig. 16.          Line block.
                      Swan Electric Engraving Co., Ltd.

  Fig. 17.          Line block.
                      Messrs. Andre, Sleigh & Anglo, Ltd.

  Figs. 18-20.      Line blocks.

  Figs. 21-23.      Line blocks.  Messrs. Bourne & Co.

  Figs. 24 and 25.  Line blocks.

  Fig. 26.          Line block.  Messrs. Bourne & Co.

  Fig. 27.          Line block.

  Figs. 28 and 29.  Line blocks.
                      Messrs. Andre, Sleigh & Anglo, Ltd.

  Fig. 30.          Line block.   Mr. C. Butterworth.

  Fig. 31.          Line block.
                      Messrs. Andre, Sleigh & Anglo, Ltd.

  Fig. 32.          Line block.   Mr. C. Butterworth.

  Figs. 33 and 34.  Line blocks.

  Figs. 35 and 36.  Line blocks.
                      Messrs. Andre, Sleigh & Anglo, Ltd.

  Fig. 37.          Line block.  Messrs. Bourne & Co.

  Fig. 38.          Lithograph reproduced by the Swelled
                      Gelatine Process.
                              Artists Illustrators, Ltd.

  Tailpiece, p. 86. Line block.
                      Messrs. Andre, Sleigh & Anglo, Ltd.




PREFACE


Modern scientific publications, although they may in some or even
many cases equal in their scientific quality the memoirs of earlier
workers, do not, on the average, reach a high standard as regards
illustration. For instance, in Great Britain botany is pre-eminent
in its morphological aspects; it should therefore follow that the
illustrations, which form so important a part of such papers, should
be beyond reproach. This is not always so, a fact which must be patent
to anyone with the slightest critical knowledge who looks through a
typical journal. This is a fact much to be regretted, since many of
the earlier scientists were accomplished draughtsmen and, indeed,
often artists; in this connection the Hookers and Professor Daniel
Oliver may be mentioned. The implication is not intended that there
are no good amateur draughtsmen nowadays; there are, and in some cases
possessed of great ability. The beautiful work of Church in his Floral
Mechanisms may be cited as an example.

It may, of course, be argued that any picture which serves to
illustrate the particular feature is good enough; this is the
contention of one who takes an insufficient pride in his work. A
feature worthy of an illustration deserves the best the author can
produce, more especially as a literary form is still, fortunately,
preserved or, at any rate, aimed at.

The reason for indifferent illustrations is primarily due to bad
or mediocre drawings, or to their unsuitability for the kind of
reproduction in view.

With regard to the first point: this lack of draughtsmanship often
obtains; when education entirely replaces mere instruction, it is to
be hoped that all students of science will be trained in the rudiments
of drawing. Meanwhile the difficulty can be partly overcome, as will
be seen later on, by the simple means of drawing on an enlarged scale,
in order that in reproduction reduction can be made.

The second reason, the onus of which also falls on the authors, is
a lack of knowledge regarding the kind of drawing suitable for the
different modes of reproduction; this is a very important point, for
"technical conditions govern even genius itself."

Authors, however, are not always to blame; it would appear that even
editors sometimes are wanting in the requisite knowledge, for we have
known straightforward line drawings reproduced by half-tone; in other
cases the paper used is unsuitable for the reproduction and, at other
times, the printers are at fault.

With a view to remedying, at any rate in part, these deficiencies, a
course of lectures, arranged by the Board of Studies in Botany of the
University of London, was delivered in the Lent term of 1913 in the
Department of Botany of University College, London.

In gratifying the wish expressed by some that these lectures should
be given a more permanent dress, the author feels that some apology is
necessary, for he can lay no claim to authoritative knowledge of much
of the subject-matter; questions relating to the graphic arts and to
illustrations, however, have always been of interest to him, so that
he has tried various experiments, often with disastrous results, and
thus has gained some experience.

In these matters the author has benefited much through his association
with Professor F. W. Oliver, who, characteristically, has been ever
ready to discuss these problems with, and to place his knowledge and
experience at the disposal of the author.

The outline of the ways and means of illustration contained in the
following pages is primarily intended for ordinary working scientists,
not for artists, professional draughtsmen or skilled amateurs.

The point of view is mainly botanical, primarily because the present
writer is a botanist and also because the requirements of modern
botany in the way of illustrations are more extensive than those of
any other science; the requirements of other sciences, however, have
not been overlooked. With regard to other branches of knowledge, the
principles considered will, it is hoped, prove of some value to the
workers therein.

The details of technique have been kept as brief as possible; in
fact, sufficient only has been said to indicate the main principles
involved. In the literature cited, to which the author is indebted
particularly for matters relating to technique, will be found full,
and sometimes exhaustive, accounts.

With regard to the illustrations, these have been selected to
illustrate the various methods of reproduction described or to
demonstrate the points raised. In those instances where the source has
not been acknowledged or the draughtsman or photographer mentioned
by name, the figure is by the author: and since the actual making
of plates and blocks is of considerable importance, the firms, when
known, responsible for their making are mentioned in the Table of
Illustrations. In this connexion the author desires to express his
appreciation of the skill shewn and care taken by Messrs. Andre,
Sleigh and Anglo, Limited, who prepared the majority of the new
illustrations which appear in the following pages.

The author is indebted to many who have helped in various ways in the
production of his work; particularly is he desirous of expressing
his warmest thanks to Miss O. Johnston for the charming drawing
of _Geranium columbinum_ (Plate 2) and to Mr. Harry Becker for
his beautiful lithograph (Plate 1). To Miss S. M. Baker, Dr. W. G.
Ridewood, and Miss Winifred Smith thanks are due for the loan of
original drawings; also to Mr. Edward Hunter and Mr. Hugh Hunter for
information regarding matters of technique and cost.

The number of illustrations would have been less but for the
generosity of Messrs. Chapman and Hall, the Editors of the "Annals
of Botany," "The Imprint," and the "New Phytologist," Professor F. W.
Oliver and Mr. G. N. Oliver in lending blocks. Recognition also must
be made of the kindness of Mr. Richard G. Hatton in consenting to the
use of certain blocks from his admirable "Craftsman's Handbook,"
of the Delegates of the Clarendon Press for permission to reproduce
figure 14, and of Messrs. Frederick Warne and Co. for permission to
make use of the wood engraving by Messrs. Edmund Evans, Ltd., of Kate
Greenaway's charming Milkmaid. Finally, the author desires to express
his sincerest thanks to Mr. Gerard T. Meynell, of The Westminster
Press, for the keen interest he has taken in the work, for his help
with the illustrations, and for the great care he has taken in the
production of the book.

  University College, London
  _January, 1915._




INTAGLIO PRINTING


In the biological sciences the massing of illustrations into plates is
still the favourite method of illustration, although text-figures have
recently become more numerous.

This is partly due to innate conservatism, for most of the earlier
memoirs were so illustrated, doubtless because it saved time, since if
wood engravings were used with a view to text-figures, the compositor
had to wait for the blocks, whereas in the case of plates the
compositor and the engraver worked independently. Also the
possibilities of plates are enormous; they may be very beautiful
indeed besides being biologically satisfactory, for much finer results
can be obtained by engraving metal than by engraving wood. Then again
there are many different processes available for the making of
plates, so that if one proves unsuitable for a subject an excellent
reproduction may be obtained by another.

Before passing on it is desirable to point out the essential
differences in the three ways of printing.

_Intaglio printing._ If the finger-tips be examined, many ridges and
furrows will be seen on their under surfaces; if now a thick ink
be well rubbed into these so as to fill well the furrows, and the
superfluous ink be wiped off from the general surface, an impression
will be obtained of the furrows on pressing the fingers on to a piece
of smooth white paper. Better still, if the copper plate of a visiting
card be examined, the name will be found cut into the surface. If an
intimate mixture of tallow and lamp-black be well rubbed into these
depressions and the excess of ink wiped off the surface of the plate,
an impression can be obtained by placing a piece of damp paper on
the plate and passing both through the domestic mangle--the kind with
rubber-covered rollers. In each case the principle is the same, the
pressure forces the paper into the depressions of the plate so that it
takes up the ink.

_Plane surface printing._ This is characteristic of lithography and
allied processes. Writing or a design well chalked on a blackboard
can be transferred on to a smooth piece of paper merely by a little
vigorous rubbing on the back of the paper placed in position over
the drawing. The transfers of childhood provide a further simple
illustration, so also does the hectograph (jellygraph).

_Relief printing._ In this case, the design is raised above the
general surface of the substance. A rubber stamp is an obvious
example.

It will be noticed that intaglio and relief are the reverse one of
the other, whilst plane-surface printing is intermediate between these
extremes. In intaglio, the ink is taken from a depression; in relief
from an elevation; and in flat printing from a plane surface.


INTAGLIO PLATES. There are several methods of making intaglio plates,
but only a few are used in the illustration of scientific papers;
attention however may be drawn to the others, not only for their
own sake, but also on account of their influence on some modern
photo-mechanical processes.


LINE-ENGRAVING. Line engraving, by which is meant cutting lines into
copper, steel, or other suitable material with a burin or graver, is
a very ancient art. Its employment for illustrative purposes is an
outcome of the art of the metal workers--particularly the Florentine
goldsmiths of the fifteenth century--who filled up the lines cut in
the metal with a black enamel of silver and lead sulphides (niello)
which was made by heating together a mixture of these metals with
sulphur. This enamel when once in was very hard to remove, so that in
order to see how their lines were progressing, the artists rubbed
well into the metal, in order to fill up the lines, a sticky ink. The
superfluous ink was then wiped off the general surface of the metal
and a piece of paper was placed in position and pressed sufficiently
hard to make it enter the depressions, which alone contained the
pigment, and take up the ink. A print was thus obtained of the work
and so its state was ascertained.

Metal engraving is carried out in the same fashion at the present
time. A flat plate of copper or steel is well polished and is worked
upon with a graver or burin, so that the picture is represented
by lines cut into the metal. Any line, however fine, will give an
impression on printing, hence it is hardly surprising that engraving
has long been a popular means of expression by artists, since force,
depth and delicacy are possible of attainment.

The printing is carried out in exactly the same way as by the early
metal workers: the plate is covered with a thick ink which is forced
well into the lines and then the superfluous ink is removed. The plate
is now ready for printing; to do this, the plate is placed in the bed
of a copper-plate press and over it is laid a sheet of damped paper
which is covered with two or three layers of blanket. The whole is
then passed under the roller which forces the paper into the incised
lines, so that not only is the ink picked out, but a mould of them
is taken on the paper, hence the very finest lines will give an
impression. Having passed through the press the paper is carefully
peeled off, and thus the print is obtained.

With regard to the metal employed, copper is commonly used, since
it is soft and easy to work; its softness however is, in a sense, a
disadvantage, since the plate will soon wear, the finest lines being
the first to go, so that a limited edition of good impressions only
is possible. To overcome this difficulty, the plate may be faced with
steel, by which means it is rendered very durable.

Steel, although once popular, is not much used nowadays owing to its
hardness and the rapidity with which it rusts. As compared with copper
engravings, steel gives a somewhat harder line, whilst copper gives
a soft line, but this, of course, does not mean that steel engravings
are harsh; the finest work can be done on steel and of remarkable
delicacy.

At the present day line engraving is seldom or never used as a means
of illustrating scientific work. It is obvious that the average
scientist has not the time and he certainly does not possess the skill
to make his own plates; the engraver must translate the originals into
lines, so that much consultation would be necessary. Further, a
line engraving takes a long time to make, and most publishers would
certainly look at the expense.

In the past, however, the line engraving was much used, and very
beautiful work was often accomplished. The following works contain
outstanding examples.

    Bojanus: _Anatome Testudinis Europaeae_, Vilnae, 1819-1821. The
    plates are beautiful engravings by Lehmann after the drawings
    by the author.

    Chatin: _Anatomie Comparee des Vegetaux_. Good steel
    engravings illustrating the structure of various plants.

    Curtis: _Flora Londinensis_, London, 1777. The illustrations
    are hand-coloured copper engravings by Sowerby and others,
    many of which, particularly the earlier ones, are of
    outstanding excellence. The engraving is often nothing more
    than the mere outline of the plant, whilst in cases where the
    structures are more massive, a certain amount of shading is
    used. The colouring is very good indeed, and it is obvious
    that much care was taken not only in the actual painting but
    also in the choice of pigments which, as far as can be judged,
    are as fresh now as when first used.

    _Curtis's Botanical Magazine_ and _Edwards's Botanical
    Register_ contain some excellent examples of hand-coloured
    copper engravings.

    Levaillant: _Histoire Naturelle des Oiseaux d'Afrique_. Paris,
    1805-8. This work contains beautifully coloured engravings by
    Feesard. The original drawings were by Reinold.

    Lyonet: _Traite Anatomique de la Chenille_. La Haye, 1762.
    The plates are amongst the best illustrative of zoological
    science.

    Martius: _Flora Brasiliensis_. The earlier volumes, _e.g._,
    Vol. 13, Part I, contain excellent engravings.

    Passaeus: _Hortus Floridus_. Arnheim, 1614-17.

    Sowerby and Smith: _English Botany_. London, 1790-1866. The
    illustrations are hand-coloured copper engravings.

    Thuret et Bornet: _Etudes Phycologiques_. Paris, 1878. This
    work contains the finest plates ever published in a botanical
    work. Riocreux drew from the preparations, and his drawings
    were engraved on steel by Picart, Thomas and others.


ETCHING. Etching is a term very loosely used; strictly speaking it
consists in corroding a metal plate or a flat stone with acid, or
other substance possessed of a kindred action, so that depressions are
formed. A pen and ink drawing, although usually so termed, is not an
etching. Briefly the method is this: a well polished copper, steel or
zinc plate is covered with a substance, known as the etching ground,
consisting commonly of a mixture of asphaltum, white wax and pitch,
which resists the action of the acid. The ground may be laid in more
than one way; the simplest, perhaps, is to dissolve the etching ground
in some solvent such as chloroform, which readily volatilises, and to
pour the solution on to the plate, which is tilted this way and that
until the liquid is evenly distributed; the excess is poured off and
what remains is allowed to dry, the plate being kept level during the
process.

The plate is then warmed until the ground is softened, when it is held
over a smoking candle and is rapidly moved here and there so that if
properly done the fine soot is evenly incorporated in the ground.
When the plate is cold, the drawing may be made by cutting through the
etching ground, so as to expose the underlying copper, with needles of
various sizes. The work is then etched by means of dilute nitric acid.

When this is satisfactorily accomplished, the ground is cleaned off,
the plate well inked with copperplate ink, and the surface ink removed
by coarse muslin. The plate is then gone over with fine muslin, but
the ink must not be removed from the depressions; finally the damped
paper is placed in position and impressions obtained by the use of the
copper-plate press.

Etching, although suitable, especially when natural-printed,[A] for
the illustration of many scientific subjects, is but seldom employed
at the present time for this purpose; the preliminary announcement
of Warburg's _Die Pflanzenwelt_, however, states that some of the
illustrations are etchings.

    [Footnote A: A plate is said to be natural-printed when all
    the ink is removed except from the depressions; in artificial
    printing some ink is allowed to remain on the flat parts.
    Artists frequently, after removing the superfluous ink,
    lightly dab the plate in order to make the pigment spread
    slightly beyond the actual limits of the depressions; this is
    known as _retroussage_.]


SOFT-GROUND ETCHING. This is a somewhat rare method of reproduction
nowadays; it may, however, be described briefly, for it would appear
to be suitable for scientific purposes, since it should not prove a
matter of great difficulty for an author who is a sufficiently skilled
draughtsman to make his own plates. The polished copper plate is laid
with ordinary ground to which is added lard in a quantity according to
the warmth of the weather.

Over the plate is then placed a sheet, larger than the plate by an
inch or two, of damp, thin, grained paper, the edges of which are
folded over and pasted to the back of the plate. When the paper is dry
it will be well stretched and in close contact with the plate. With
the hand resting on a bridge, in order to avoid inadvertent touching
of the plate, the drawing is made on the paper with a pencil of a
hardness suited to the softness or otherwise of the etching ground.
When the drawing is finished the paper is carefully removed; wherever
the pencil has been used, the etching ground will adhere to the paper,
so that in such places the metal will be exposed. The plate is then
etched and printed as in the normal process.

No reproductions of drawings of scientific subjects apparently have
been reproduced by this method. Examples can conveniently be examined
in _The Seven Lamps of Architecture_ by Ruskin.


MEZZOTINT. The characteristic feature of mezzotint is that the
subject is translated into tones rather than lines as in the preceding
intaglio methods.

The surface of a smooth metal plate--usually copper--is raised into
innumerable and minute projections by going over it in all directions
with a curved steel tool, known as a rocker, the edge of which is
finely toothed. An impression taken of the plate in this condition
will give a deep rich tone. The high lights are obtained by scraping
and burnishing away the elevations so that there are no pits left
to hold the ink, and, similarly, intermediate tones are produced by
partly removing the pile so that the pits are made of varying degrees
of shallowness and consequently will print in tones according to their
depth.

Impressions are taken in the same way as in the case of etchings.

Mezzotint apparently has never been used for the reproduction of
scientific subjects. Indeed, in a sense, this process is much too
artistic for the purpose. At their best, illustrations reproduced
by this method have mystery and depth and give the imagination
much employ; in a word, they are subjective rather than objective,
qualities unsuited for our purpose.


PHOTOGRAVURE. Photogravure may next be considered, for although it
is a photo-mechanical process, it corresponds to mezzotint. Excellent
results may be obtained by its use provided the drawings--usually
executed in monochrome such as sepia--be really good, otherwise they
are hardly worth reproducing by this relatively expensive method.[A]

    [Footnote A: This account refers only to plates made and
    printed entirely by hand, not to photogravure for printing on
    a rotary machine.]

Photogravure is particularly suitable for the reproduction of drawings
showing a large amount of detail and made up of a variety of tones
rather than lines or stipple.

The photographic part of the process is essentially the same as making
a carbon print from a photographic negative. This consists in exposing
under the negative the carbon tissue, which is a mixture of gelatine,
in which is dissolved bichromate of potash, and a suitable pigment.
Such a film of bichromate gelatine is, when dry, sensitive to light.
If no light gains access to it, the gelatine is readily soluble in
warm water; if light acts upon it, the gelatine becomes insoluble in
proportion to the degree of its exposure. Obviously, the pigment will
be retained in varying degrees according to the relative insolubility
of the different parts of the gelatine.

The carbon tissue having been exposed, is rolled down on a wet sheet
of paper covered with some adhesive and is dried under pressure. The
paper is then soaked in warm water when the basis of the carbon tissue
easily peels off; the picture is developed by laving in warm water,
which will dissolve the gelatine in proportion to its exposure to
the light. The print when dry is remarkably permanent and, from the
picturesque point of view, is infinitely superior to the ordinary
silver print.

The method of making the photogravure plate is, in outline, as
follows:

The original drawing is photographed, and it is very important that
the negative should be as perfect as possible.

From the negative, a positive is made upon transparency carbon tissue
which is mounted upon a sheet of plate glass. The procedure is, in
essentials, exactly the same as described above for the making of a
carbon print. This positive when dry may be touched up; after which
a negative, which also may be touched up, is made from it upon an
ordinary sheet of carbon tissue.

The negative so obtained is transferred to a prepared plate of copper,
developed with warm water and dried.

The copper plate is prepared as follows: after being well polished
until quite free from all scratches, the surface is dusted over with
finely powdered resin or, more usually, bitumen. The plate is then
heated until the dust adheres.

After the carbon negative has been stuck on to the plate, developed
and dried, the margins and back of the copper are protected with an
acid-resisting varnish. When dry, the plate is placed in the etching
bath of nitric acid or, more generally, of ferric chloride. The
etching fluid will pass through the thinnest parts of the negative
first, so that the surface of the copper will be etched to a degree
corresponding to the thickness of the gelatine. The high lights on the
negative obviously will be represented by thick coatings of gelatine,
consequently such parts will be but slightly etched and vice versa.

If the plate had not been laid with resin, the surface after etching
would show more or less extensive depressions and elevations; but the
grains of resin protect the copper immediately beneath them from the
action of the acid, which consequently can only dissolve the exposed
parts of the metal between the resinous particles. The result is,
therefore, that the plate is covered over with numberless fine pits of
varying depths. The deepest ones will, on printing, give the darkest
tones, since they will hold more ink, the shallower ones will give
the lighter tones, whilst the shallowest and those parts unetched will
give the high lights.

The plate is usually etched three or four times successively in
varying strengths of fluid, after which the etching ground and
gelatine is cleaned off.

A strong copper-plate ink is then well rubbed in by means of a dabber,
after which the ink from the surface is removed, first with a coarse
piece of muslin and finally, with fine muslin. The ink must not be
removed from the pits.

The first pull is then taken as in a line engraving with a
copper-plate press, and its appearance shows what corrections are
necessary. The plate nearly always requires a certain amount of
engraving; the high lights may be improved by means of a burnisher,
the shadows by means of a rocker or a roulette--a small steel wheel
the rim of which is beset with fine teeth--and so on. Finally, if a
large edition is required, the plate is steel faced.

Although much used for the reproduction of pictures, photogravure is
too rarely employed for scientific purposes; this is to be regretted,
for the process is admirably suited to the reproduction of photographs
and drawings with delicate tones. As compared with the usual
half-tone, the cost is high, and this no doubt militates against its
use.

Examples of outstanding excellence will be found in the _New
Phytologist_, Vol. xi, 1912, plates 5 and 6. These are absolute
facsimiles of the original drawings by Mr. McLean, both as regards
colour and reproduction of tones. Plate 8 may also be examined and
compared with plates 9 and 10 which are reproductions of the same
subject in collotype and half-tone respectively.




PLANE SURFACE PRINTING

[Illustration: PLATE 1.--An original lithograph by Mr. Harry Becker.]




PLANE SURFACE PRINTING


LITHOGRAPHY. Of these methods of printing, lithography is the
outstanding example: it is a method of reproduction possessed of great
possibilities, for by its employment a facsimile of any drawing can be
obtained.

As a means of artistic expression it ranks high amongst the graphic
arts, and, for the reproduction of drawings of a scientific nature, it
is very popular, since it meets most requirements and is comparatively
inexpensive.

The art, which was discovered by Senefelder towards the end of the
eighteenth century, depends on the fact that grease and water are
immiscible: a drawing made with a greasy pigment upon a suitable
surface adheres very strongly, whilst those parts free from it retain
water, so that when damped and rolled up (_i.e._, inked), the ink used
will stick only to the lines, etc., of the drawing, but not to the
other parts.

Clearly the surface is all important, and this is provided by
lithographic stone, a limestone occurring in Germany, France, England
and Canada. The best stones occur at Solenhofen near Munich, those
from other localities being inferior in quality. Incidentally it may
be mentioned that zinc and aluminium plates are not infrequently used
in place of stone.

Lithographic stones vary in hardness, colour and grain. For the best
work the stone should be homogeneous and of a hardness suitable for
the subject; the colour affords an indication of the hardness, the
lighter-coloured stones, which are much the commoner, being softer
than the darker.

There are two modes of procedure; the drawing may be made direct on
the stone with lithographic ink or crayon--both being mixtures of
tallow, wax, soap and shellac, with a sufficiency of pigment to render
the drawing visible to the artist--or else the drawing may be made
upon transfer paper.

The former method, although the more satisfactory and often used
by artists, is seldom pursued in scientific drawings except when
professional draughtsmen are employed. In such cases it may be
necessary to reverse the drawing, which is conveniently done by
viewing it in a mirror, and, of course, all lettering must be
reversed.

The majority of amateur draughtsmen make their drawings in pencil or
ink and these the lithographer traces upon lithographic transfer paper
and transfers them to the stone; he, the lithographer, may merely
trace the salient features and work the drawing up on the stone. The
transfer papers are coated with gelatine, starch or gum, or mixtures
of these substances, the idea being to interpose between the real
paper and the pigment--in the form of lithographic crayon or ink--some
substance soluble in water which will hold the pigment and prevent
it soaking into the paper, so that a transfer has only to be damped
through the back, pressed on to the stone and peeled off. The work,
together with more or less of the film, will thus be transferred on to
the stone and, of course, will be reversed, since the part uppermost
on the stone will be the back of the original drawing.

The original drawings may be made upon the transfer paper direct, and
in so doing mistakes in tracing will be obviated. Suitable papers are
made for various purposes, e.g., smooth for ink work and variously
granulated for crayon (see Plate 1, which was drawn by Mr. Harry
Becker on transfer paper).

Another advantage in drawing directly upon the transfer paper is that
the draughtsman can make corrections pretty easily for, if needs be,
a bad piece of work can be entirely cut out and a fresh piece of paper
inserted.

Assuming that the transfer method has been employed, the stone must be
prepared according as the drawing is made with ink or with crayon.

The stone is first thoroughly ground, in order to rid it of all traces
of previous work, and then polished for ink work or grained--_i.e._
roughened--for crayon work, the small points produced taking up the
crayon in proportion to the amount present on the transfer and the
pressure used.

The transfer is then damped with water, sometimes with a dilute
solution of nitric acid, and placed in position on the stone, which
is then passed two or three times through the lithographic press until
dry. Then the back of the paper is damped and the sheet peeled off.

The stone is next proved, _i.e._, prepared for printing.

It is first carefully examined for broken lines and other blemishes,
which are touched up with ink or crayon. The stone is then painted
over with a solution of gum in water which is allowed to dry, it is
then washed in water and rolled up with ink. The drawing will now be
clearly visible, for if properly inked the clear parts of the stone
will not take the pigment, so that any parts which require cleaning
up may be deleted. This is accomplished by means of a pencil of snake
stone, a piece of pumice stone, an acid stump--a rod of hard wood, the
sharpened end of which is dipped into nitric acid--or with a scraper.
The stone is again washed and rolled up strongly with ink and etched
with a dilute solution of nitric acid which is applied with a sponge;
then the surface is again gummed and the stone allowed to dry. It is
sometimes necessary to re-etch the stone; if so, the damp stone is
rolled up with thin ink and allowed to dry, it is then dusted over
with finely powdered resin, the superfluous resin is removed by means
of a wet sponge, and the surface is painted over with a solution
of gum arabic mixed with dilute nitric acid. If the resin is well
incorporated with the ink, the work will suffer no damage in the
process. The acid gum is then dabbed off with a rag, the stone is
cleaned up with turpentine, rolled up once more, gummed and finally
set aside to dry.

All this appears complicated, but it is very necessary to get a good
surface for printing. The action of the gum does not appear to be
clearly understood, the nitric acid obviously will etch the stone, so
that the gum will easily penetrate. It is sometimes supposed that the
arabic acid of the gum enters into a chemical composition with the
calcium carbonate, making a film which is the real ink-resisting
surface. This film has not a long life, so that in printing it is
necessary to renew it periodically by the application of gum solution.

If possible, the stone should be allowed to rest for a day or two
after proving, in order that the ink may sink well in.

Before printing, the gum is washed off and the stone allowed to
remain in the press-room until its temperature is the same as its
surroundings. The stone is then thoroughly and evenly damped all over,
placed in the press, and rolled up with lithographic ink; the paper
is then laid on, and the whole passed through the lithographic press.
After the first few pulls it will be seen whether all is well. The
essentials of a good impression are these: the lines must be black and
not grey, provided black ink is used; the lines must not be wider or
blacker ("smutty") than those on the stone, nor must they be ragged or
broken ("rotten").

In printing, the stone must be damped and inked before each impression
is taken, and occasionally re-gumming is required. Good printing
requires a considerable amount of ability, especially in the case of
crayon drawings.

The paper used is a very important matter, the selection of which can
be safely left to the lithographer, provided he be a good one, unless
the author possesses the necessary technical knowledge. If a smooth
paper is required, and the paper is not to be damped before printing,
India paper is best and plate paper next best. All coarse or grained
papers must be damped before printing.

As has already been remarked, lithography is a good process for
scientific work; but, unfortunately, considering the number of
lithographic plates published, really first-class examples are rare.
This is largely due to the original draughtsman; it is unreasonable to
expect a lithographer, in all probability ignorant of the subject of
the plate, to turn out first-class reproductions of drawings which are
obviously bad. On the other hand, lithographers vary greatly in their
capabilities, and indifferent plates may be entirely due to their
ability not being first rate.

As drawings have to be traced, mistakes are apt to occur; the proofs
should, therefore, be carefully examined, for a certain amount of
correction can be made on the stone.

The following works contain excellent lithographs, which should be
studied by those interested in the subject.

    Bornet et Thuret: _Notes Algologiques_. Paris, 1876-1880. This
    contains some of the best work, illustrative of science, known
    to the present author. The original drawings mostly were
    made by Bornet, and the lithography was carried out by
    Riocreux--one of the best if not the greatest of botanical
    artists--Arnoul, Picart and Pierre.

    Davis and Thurnam: _Crania Britannica_. London, 1865.

    Mirbel: _Sur le Cambium_, Paris, 1842. The plates provide
    excellent examples of ink lithography by Laplante.

    Von Mohl: _Schriften botanischen Inhalts_. Tuebingen, 1845.
    Good examples by Federer.

The first volumes of the _Annales des Sciences Naturelles_ (Paris) may
be referred to for lithographic work earlier than the above (1820).

For more modern examples the following may be consulted:

    Blackman and Welsford: _Fertilisation in Lilium_, Annals of
    Botany, Vol. 27, 1913.

    Gravis: _Recherches anatomiques sur les organes vegetatifs de
    l'Urtica Dioica_, Bruxelles, 1885. This memoir contains both
    good and indifferent plates.

    Keibel: _Normentafeln zu Entwicklungsgeschichte der
    Wirbeltiere_, Jena, 1904.

    Reed: _A Study of the Enzyme-secreting Cells in the Seedlings
    of Zea Mais and Ph[oe]nix dactylifera_. Annals of Botany, Vol.
    18, 1904.

    Semon: _Zoologische Forschungsreisen in Australien_, Jena,
    1904.

    Vaizey: _On the Morphology of the Sporophyte of Splachnum
    luteum_, Annals of Botany, Vol. 5, 1890.

    Woodburn: _Spermatogenesis in Blasia pusilla_, Annals of
    Botany, Vol. 27, 1913.

Several memoirs in the _Fauna und Flora des Golfes von Neapel_
(Berlin) are illustrated by excellent lithographic plates. Many good
examples of chromolithography also will be found there.


CHROMOLITHOGRAPHY. Lithography is much used for the reproduction
of coloured pictures and illustrations, the process being termed
chromolithography. The principles involved are the same as for
ordinary work, but it is necessary to print from several stones, one
for each colour. It is obvious that much skill is required, for the
employment of different colours will give a large number of secondary
and tertiary tints when printed one above the other in various
combinations. Thus, by printing part of a design in yellow and
the other part in blue, the finished product would show three
colours--yellow, green and blue, and by the use of three primary
colours a large number of different tints may be obtained.

As already mentioned, each colour is printed by a separate stone,
there is thus no limit--excepting that of expense--to the number of
different colours which can be obtained.

In practice it is usual to make an outline of the essential parts
of the composition on a stone, known as the keystone, which is not
necessarily used in printing the picture. An impression of this
outline is taken upon a sheet of paper, which is used to transfer the
design on to the stones, on each of which the artist will draw only
those parts which he desires to be printed in one particular pigment.

Although the sequence of colours is generally blue, red and yellow, it
is obvious that various changes in this order must be made according
to the colours used and the exact tint required. For instance, a
body colour such as cadmium yellow would precede a glaze such as
madder-lake; again, two distinct tints may be obtained from red and
blue, for example, according to the order of printing--red upon blue
will give a mauve, whilst blue upon red will give a purple.

A knowledge of pigments is thus all important, and in printing, the
superposition must be perfect.

Plate 2 is an example of a chromolithograph. Miss O. Johnston first
drew the outline of the plant, which was phototransferred on to the
stone. An impression was then pulled and tinted by the artist,
and from this tinted impression the colour stones were made by the
lithographer. It may be added that only three colours were used in
printing the plate.

Examples:

    Baur: _Einfuehrung in die experimentelle Vererbungslehre_
    (Plate 1). Berlin, 1911.

    Bruce and others: _A Note on the Occurrence of a Trypanosome
    in the African Elephant_. Proceedings of the Royal Society of
    London, B. Vol. 81, 1909.

    Cropper: _The Development of a Parasite of Earthworms_. _Id._
    Vol. 85, 1912.

    Oliver: _On Sarcodes sanguinea_. Annals of Botany, Vol. 4,
    1889-1891.

    Rubbel: _UEber Perlen_ ... Zoologische Jahrbuecher, Vol. 32,
    1911-12.

    Biometrika, 1906-7, Vol. 5, Plate 23.

Mention has been made of the value of a knowledge of colours. The
subject is much too extensive to be considered adequately on the
present occasion even if it were desirable; its importance, however,
warrants a few passing remarks.[A]

    [Footnote A: See Ridgway: _Color Standards and Color
    Nomenclature_.]

No two people will describe in the same way the colour of, say, a rose
petal; both will have a different conception of the colour "crimson."
The majority have but a limited sense of colour, and even when this
faculty is possessed, the personal equation looms large; further,
the ordinary names of colours are quite inadequate for descriptive
purposes. For these reasons the importance of a scientific system of
colour nomenclature and colour standards is all important. By the
use of such a scheme, the exact colour of an object can be found
by comparison with an adequate chart, and the name there given will
convey to others exactly what colour is described or desired. The
plumage of a bird or the colour of a flower can thus be described
correctly, and an author can indicate exactly the colour desired in
certain parts of a chromolithograph or other reproduction in colour.


[Illustration: PLATE 2.--GERANIUM COLUMBINUM.

A chromolithographic reproduction of a drawing by Miss O. Johnston]

PHOTOLITHOGRAPHIC PROCESSES.--Of these methods of reproduction there
are several, their value lying in the fact that the originals can be
reduced or enlarged with the greatest of ease. The general principles
are as follows.

A photographic negative is taken of the original drawing and a
positive made on a film of bichromate gelatine. Wherever light reaches
the film, the gelatine is rendered more or less insoluble according to
the intensity of the light acting upon it; through the dark parts of
the negative but little light will pass, so that the gelatine will
remain soluble.

The exposure of the positive having been made, the film, which may be
mounted on paper, is inked with lithographic ink in the dark room and
then washed. The pigment will adhere to those parts acted on by light,
but will wash away from those regions unacted upon; obviously the
half-tones will retain ink in direct proportion to their density.

The developed positive is then transferred to a stone or zinc plate
and impressions taken as in pure lithography for the dark parts are
resistant to water and will take the ink, whilst the high lights will
retain water and so will not be inked. The intermediate tones will
take the pigment according to their density.

In distinction to the previous methods, corrections cannot be made
except in so far as the negative can be touched up.


COLLOTYPE.--Of the various photolithographic methods which have from
time to time been employed, collotype is the one in most general use
at the present time, especially for the reproduction of photographs.

Collotype is a simple process which does not require so extensive a
technical knowledge and ability as some of those previously described.
But notwithstanding this, the results are sometimes unsatisfactory
and unequal; faults due to indifferent originals and to unsatisfactory
conditions obtaining in the work rooms. The great drawbacks to good
collotype are cold and dampness, and it is for these reasons that
continental firms, blessed with a more stable climate, often produce
much the best work. Provided the workshops are properly heated, the
collotypers of this country ought to be able to turn out good work at
all times of the year; indeed, the best firms do.

For this and for other processes in which photographs form the
originals to be reproduced, authors should send the negative to the
collotyper; if this be impossible, positives of the best possible
quality, printed on ordinary P.O.P. paper, toned to various shades
of purple, and also on smooth bromide paper, in ordinary black tones,
should be provided in order that the collotyper can choose the print
he most prefers to work with. Also, it is usual to glaze the prints.

The method is as follows. A piece of british plate glass, about
half-an-inch in thickness, is ground on one side with fine emery
powder, and then thoroughly washed and dried. The plate is covered
with a filtered mixture of the colloids sodium silicate and dextrine
or albumin, and placed in a warm oven to dry. If metal plates are
used, such as zinc or copper, this preliminary coating is unnecessary;
glass plates, however, must have the substratum in order that the
sensitised gelatine--which is next put on--may stick.

When the plate is dry, it is thoroughly washed with water in order to
remove any free silicate; it is then dried and put away until required
for use.

The sensitising solution is made up of gelatine and bichromate of
potash dissolved in water; before use it is filtered, freed from air
bubbles and heated to not more than 120 deg. F. The plate is now placed
on a stand, which is provided with levelling screws, in the oven, and,
when the temperature has reached 120 deg. F., an amount of the bichromate
gelatine solution sufficient to make a thickness of film proper for
the mode of printing to be employed is poured upon the plate.

The oven is kept at a constant temperature, 120 deg. F., until the
gelatine is dry, when it is allowed to cool gradually.

Whilst the gelatine is setting, precautions against vibration must be
taken else the plate will be spoilt.

When dry, the collotype plate is sensitive to light and moisture;
its surface shows a more or less regular series of convolutions which
resemble those of the outer surface of the human brain, although,
of course, very much smaller. The character of the grain is very
important, for if it be too fine it will not take up a sufficiency
of ink, and, on the other hand, if too coarse it will yield coarse
impressions.

A reversed negative, of a quality beyond reproach, must be made of the
original; if the subject is dark or has heavy shadows the negative is
frequently slightly over exposed so as to soften them.

The collotype plate is then exposed under the negative and washed in
cold water until the yellow bichromate no longer comes away. It is
then dried.

In printing, the plate is damped and rolled up with ink as in
lithographic printing; the amount of ink adhering to the film depends
on the extent to which the different parts have been acted on by
the light, as has already been mentioned. The moistening of the
plate--mis-termed etching--is best done with dilute glycerine
containing 75 per cent. of water, which when first applied should be
allowed to remain on for about half-an-hour. The excess of moisture is
taken up with a sponge or a ball of rag, and then the plate is inked
and printed in a lithographic or a collotype press. The picture is
usually masked with tin foil in order that its edges may be quite
clean.

Of the faults which may occur, the following may be alluded to. A
mottled appearance may obtain in the high lights; this is due to the
coating of gelatine being too thick. More commonly, the reproductions
may appear flat owing to the degradation of the high lights; this is
a sign that the sensitive film has been acted upon by moisture during
its critical existence between the drying and the washing out of the
potassium bichromate, or that the temperature has been too low.

The following contain good examples of collotype.

    Karsten and Schenck: _Vegetationsbilder_, Jena.

    Oliver: _Notes on Trigonocarpus and Polylophospermum_. New
    Phytologist, Vol. 3, 1904.

    Semon: _Zoologische Forschungsreisen in Australien_. Jena.
    1912.

    Thompson: _The Anatomy and Relationships of the Gnetales_.
    Annals of Botany, Vol. 26, 1912.

    See also Plates 3, 4, 5 and 9 in the present work.


THE PREPARATION OF ILLUSTRATED PAGES. Of the processes dealt with,
photogravure lithography and collotype are those most generally used
at the present day for the printing of plates or insets. Half-tone
also is employed, a process which will be considered later since it
is essentially relief printing. This, therefore, is a convenient
opportunity to make a few general observations on plates.

Plates should only be employed for the reproduction of subjects of
such complexity that cannot be reproduced satisfactorily by figures in
the text.

A plate or page made up of several illustrations should look well as
a whole; in other words, it should not outrage all the canons of
composition, it should have some pictorial effect. At the same time,
for facility of reference, the individual figures should run in a
convenient sequence. This latter point is so important that a plate
composed really well is distinctly rare, for a compromise nearly
always has to be made. At the same time there are, apparently,
comparatively few authors who pay much attention to plate design.

Although it is not desired to write of the laws of pictorial
composition, attention may be drawn to a few points which are amongst
those generally neglected.

The figures should not be crowded together; a reasonable amount of
margin should be left around each. They should be arranged, as far as
possible, in such a way that a sense of balance is maintained. As
to how this is to be accomplished will depend upon the nature of the
illustrations; if they are all about equal in tone, the largest ones
should preponderate towards the base of the plate, and not _vice
versa_. The difference which this makes will be obvious if the two
accompanying illustrations (Figs. 1 and 2, Plate 3) be compared. The
first is a reduced copy of the plate as it was published: it will be
noticed that it has a top-heavy appearance, which is corrected in the
second figure by the simple device of turning it upside down.

[Illustration: PLATE 3.]

If, on the other hand, the figures are some lighter and others darker,
the latter should form the base, since low tones give the idea of
solidity; this is so marked that in cases where the figures vary much
in size and tone, the darker ones may nearly always be situated at the
base or at any rate low down on the plate unless they are very much
smaller than the lighter toned ones.[A]

    [Footnote A: If, of course, the reader understands
    chiaroscuro, he will take no notice of this paragraph, but
    arrange his plates in accordance with his ability.]

An examination of the figures on Plates 4 and 5 will roughly
illustrate these points. The upper figure of Plate 4 is well designed,
and no improvement could be made, bearing in mind the compromise
alluded to above. The lower figure is, however, not so good, it was
obviously a difficult one to arrange; it would have been improved if
Figs. 23, 26 and 28 could have been placed in the top tier, but this
would have seriously disturbed the sequence. The first illustration
on Plate 5 is well designed; it would, however, have been improved by
interchanging 8A and 11B.

[Illustration: PLATE 4.]

[Illustration: PLATE 5.]

We may now pass on to the individual figures; these should shew the
essential features, together with some surrounding and comparatively
extraneous matter; often there is included too much of unimportance
and its retention means a waste of valuable space. The first thing to
do, therefore, is to trim, if needs be, the figures; their shape is
more or less immaterial, provided that in cases where there are a
large number of illustrations on one plate, they are not all alike.
The American fashion of circular figures is particularly displeasing,
at any rate to the author.

Having trimmed the figures, the next point to decide is whether any
require reduction; if they do, cut out pieces of paper (referred to as
patterns below) of the size which the figures will ultimately appear:
on the whole, it is better to avoid reduction of the originals,
for without a good deal of experience it is very difficult to judge
exactly what the result will be; a good idea, however, may be gained
by the use of a diminishing glass.

The size of the available surface of the plate should now be ruled
on a white sheet of fairly thick cardboard, and the figures, or their
patterns, arranged so as to be easy of reference, to compose as well
as may be, and spaced in such a way that, in the case of a quarto
plate to be folded vertically, no figure is placed so that the fold
will pass through its centre. Nothing is more irritating than having
an illustration spoilt in this way.

All this may be done by arranging in different ways until a
satisfactory result is obtained, a process which may take an hour
or two. The figures should then be pasted down, covered with several
sheets of blotting paper and placed in a press. A press is seldom
available; when such is the case, a number of heavy books serve
equally well.

The lettering must next be attended to. The individual figures are
usually designated by numbers; this is a bad method, since it involves
referring to the description of the plate. The best way is to use a
number, and after it to add the name of the plant or animal, and, if
needs be, a description as short as may be. If the author can "print"
or write reasonably well, well and good; if not, it is better to
attach a slip to the plate with full directions relating to lettering,
and to write in pencil on the plate the titles, etc., required in the
proper places for the guidance of the craftsman. The typewriter is
sometimes employed for this purpose by authors; it is purely a matter
of taste, but some readers feel a slight shock when this method is
resorted to.

In some cases a key to the plate printed on tough translucent tissue
paper and having the necessary information, guide lines, etc., is
inserted with the plate.[A]

    [Footnote A: See Kerner and Oliver: _Natural History of
    Plants_ (First Edition) London, 1894.]

In the case of glossy chromolithographs this practice is best avoided,
for the key is apt to stick to the plate if too much pressure is used
when the book is bound.

With regard to the "catch letters" used to indicate different parts:
these should be as obvious as possible, and the guide lines should be
either in black or in white ink, according to the general tone of the
illustration. These lines should be conspicuous without being heavy.
Not infrequently they, together with the lettering, are printed on the
plate by a second impression in red ink.

The foregoing is primarily the business of the author; with regard to
editors and publishers, all plates should be mounted in a manner to
facilitate reference and should be printed on suitable paper; the
former is seldom or never done. All plates which must be constantly
referred to in reading the text should have a selvedge as broad as the
book, so that when unfolded the whole plate is visible, no matter what
page is being read. This would, no doubt, prove an additional expense,
but this should not militate against the suggestion here made, not by
any means an innovation, for in many cases it would save the expense
of mounting on guards, and, further, the additional expenditure could
be saved several times over in other ways.

With regard to paper, this generally is satisfactory; unfortunately,
highly glazed paper, mis-termed art paper, with an enamelled or chromo
surface, and consisting chiefly of china clay and size, is generally
used for printing the best half-tone reproductions. For this purpose
a paper with a suitable surface, obtained by means other than those
mentioned and not too costly, is highly desirable, since art paper has
the reputation of being not at all permanent, owing to the deleterious
action of moisture, and is somewhat brittle. When used, art paper, if
folded, should have a proper paper hinge along the fold.

Half-tones are occasionally printed on a kind of vegetable parchment,
a paper which should be more extensively used since it will sometimes,
but not always, give as good a reproduction as art paper, and the
final result is more pleasing from the artistic point of view.

[Illustration: G. Oliver, del.]




RELIEF PRINTING

[Illustration:

  Little maid, little maid,
  Whither goest thou?
  Down in the meadow
  To milk my cow.

Fig. 1.--A wood engraving, by Edmund Evans, from the original drawing
by Kate Greenaway.

Reproduced by permission of the publishers, Fredk. Warne & Co.]




RELIEF PRINTING


In order that illustrations may be incorporated in the text, the
blocks used must be in relief the same as the type; a mixture of
intaglio and relief is impossible, for the whole surface must be level
in order to be inked by the rollers, which deposit the pigment evenly,
so that only one tone of colour--that of the ink--is possible.

Up to quite recent times wood cuts and engravings were the only means
available for text-illustrations, so that this method may next be
considered.[A]

    [Footnote A: See Treviranus, C.L.: _Die Anwendung des
    Holtzschnitts zur bildlichen Darstellung von Pflanzen_.
    Leipzig, 1855.]

WOOD CUTS AND ENGRAVINGS. The invention of illustrating by means of
wood blocks followed closely on the heels of the use of moveable types
for printing. The Chinese were the first, as far as is known, to use
these methods of printing and illustration; in the western world the
first wood blocks date from the beginning of the fifteenth century.

All the earlier cuts were made, commonly on pear wood, on the
longitudinal face of the wood, in technical language "on the plank,"
and seemingly, in many instances, were made from drawings in ink. By
cutting on the plank, the craftsmen were enabled to make large blocks,
but were prohibited from doing anything more than relatively simple
and straightforward work. Such blocks are known as wood cuts; wood
engravings were not made until the possibilities of a hard wood like
box carved upon the transverse section were discovered at a much later
date. This is, strictly speaking, wood engraving, an art which almost
entirely, if not quite, superseded the older craft, on account of its
great possibilities; indeed, wood engravers imitated metal engraving
so closely as to deceive many. But such work was enormously laborious;
for instance, in the case of a fishing net, if the string were to be
printed black, the engraver would have to cut out hundreds of small
diamond-shaped pieces of wood in order that the string of the net
should be in relief. But few artists would do this of their own
free will, and generally such laborious work will only be found
in wood-engravings which were intended for the reproduction of ink
drawings or other kinds of pictures where the lines, shading, etc.,
had to be faithfully copied. This point may be illustrated by the
accompanying cut (Fig. 2), which was made by my friend Mr. Geoffrey
Oliver, who at the time was totally uninstructed in the art and
knew nothing of its literature. It will be seen that he, quite
unconsciously, treated his wood in the same way as an engraver would
his metal; the result, of course, is just the opposite to metal
engraving since the printing of the wood block is the reverse to
intaglio.

[Illustration: Fig. 2.]

In fact, the cut illustrates the three fundamentals of wood engraving;
the white line made by cutting out the wood so that no impression will
be obtained when printed; the white space which is similarly obtained;
and the black space, which is made by leaving the wood untouched. It
was, however, necessary to employ the black line, otherwise the tape
with which the two men--the artist and his father--are measuring the
trunk of the tree would be invisible where it crosses the sky. In a
word, the little picture illustrates very nicely the legitimate use of
wood in the graphic arts.

As already remarked, the majority of the earlier wood cuts and
engravings are reproductions of line drawings, so that although we may
admire and often marvel at the technical ability of the engraver, the
credit for what artistic merit such illustrations may possess must, in
the majority of cases, go to the draughtsman.

The work of the earlier wood engravers may be conveniently studied in
_A Lyttel Booke of Nonsense_, by R. D., London, 1912. (See also the
relevant works cited under Literature, p. 94).

Bewick, of course, is an outstanding example of an artist who used
wood engraving for illustrating natural history; the methods he
pursued may be studied in the tailpiece on p. 11, which was printed
from an electrotype of the original block.

Wood engraving, up to quite recent times, was the method of
reproducing text figures; not only for scientific books and
periodicals, but also for general literature and journals.

Much of this work is of outstanding excellence; for scientific work
the following may be studied:

    Duchartre: _Elements de Botanique_. Paris, 1867. The drawings
    were made by Riocreux and engraved by Leblanc.

    Baillon: _Histoire des Plantes_, Paris, 1887. This work
    contains some beautiful wood engravings, reproductions of
    drawings by Faguet.

    Bentham: _Handbook of the British Flora_, London, 1865. The
    engravings are from drawings by W. H. Fitch.

    Deschanel: _Natural Philosophy_, London, 1890. The engravings,
    many of which are of excellent quality, are by Laplante,
    Rapine and others. In many cases, notably in the
    representation of the rays of light passing through lenses
    and also in the illustrations of snow crystals, the use of the
    white line is admirably demonstrated.

    Kerner: _Pflanzenleben_, Leipzig, 1888. This contains some
    excellent engravings by Winkler and others.

    Le Maout et Decaisne; _Traite general de Botanique_, Paris,
    1876. This work contains splendid examples by Riocreux and
    Steinheil (see Fig. 8).

    Oliver: _First Book of Indian Botany_, London, 1869. This
    contains some characteristic work of W. H. Fitch.

It does not appear to be generally known that excellent reproductions
in colour may be obtained from wood blocks by superposed printing in
a manner comparable to that followed in chromolithography although, of
course, in the present instance, the blocks are in relief (Fig. 1).

From the foregoing account it is obvious that the engraving even of
a small illustration, except it be in mere outline, involves a
considerable amount of labour; in fact, if the subject were large
it was usual to cut it up into areas and distribute between several
engravers, the finished blocks finally being joined together to make
the block of the whole picture. Hence it is not surprising to find
that when the photo-mechanical processes were perfected, the older
methods of reproduction were ousted by the newer, more especially
since they are much less expensive; these, therefore, may next be
considered.


THE HALF TONE PROCESS.--For the making of a relief block by
photo-mechanical means, the main difficulty is the proper rendition of
the tones intermediate between black and white; this has been solved,
at any rate in part, by the discovery of the half-tone process.

If an ordinary photographic negative be highly magnified, it will be
seen that the high lights, the low lights, and the intermediate tones
are made by the varying density of the reduced silver. In the lighter
parts the small black particles are surrounded by colourless areas,
whilst in the dark regions small colourless patches are surrounded by
black areas owing to the closeness of the particles of silver (Plate
5, Fig. 2).

What is required, therefore, is a relief block which will print
a number of dots of equal density but of unequal size. Vervasser
illustrates the point in an ingenious way: a plate, covered with a
number of cones, is supposed to be acted upon by light in such a way
that the cones are truncated in varying degrees according to intensity
of the light falling upon them. The section of such a plate would
therefore shew a curve (Fig. 3); now if the truncated cones be brought
down to one level and a print taken from them, the high lights would
be represented by black dots surrounded by white areas and so on.

[Illustration: Fig. 3]

This illustrates the principle which obtains in the making of
half-tones in which the image is made up of a large number of dots
varying in size but all equally dense, so that when viewed from a
suitable distance the dots are individually invisible but compose
to give gradations of light and shade. In other words, the structure
obtaining in a photographic negative is, in a sense, realised by
optical chemical means, although the dots in a half-tone block are
much coarser than those in a negative (Plate 5, Fig. 3).

This result is obtained by interposing between the diaphragm of
the camera and the negative--for the half-tone process is a
photo-mechanical one--a glass screen covered with intersecting
engraved lines (Fig. 4). As a matter of fact, each screen consists of
two plates of glass similarly ruled and cemented face to face so that
the lines intersect.

[Illustration: Fig. 4]

It may at first be thought that the effect of such a screen placed in
front of the negative would be to produce merely a cross hatching on
the reproduction; this, however, is not the case; if the screen be
placed in a proper position relative to the negative and the size
of the diaphragm of the camera, the picture will be reproduced in a
series of dots of varying size.

The optical and other reasons for this phenomenon must be sought
elsewhere,[A] but the following brief consideration will serve to
illustrate what happens. The rays of light which ultimately reach the
sensitive plate are acted upon by two lenses, that of the camera and
the meshes of the screen, each one of which acts as a lens on the
principle of the pin-hole camera. Each mesh, therefore, brings the
image of the diaphragm to a focus on the negative, but the lens of
the camera focusses the picture as a whole, thus the amount of light
falling on the different pin-holes will vary in intensity, and hence
the dots produced will vary in size, for it is assumed, with good
reason, that each dot is built up from its centre and radially expands
according to the amount of light acting upon it.

    [Footnote A: See Verfasser, _loc. cit._, p. 94.]

It is obvious that the quality of the resulting picture will depend,
other things being equal, upon the coarseness of the screen employed.
Screens are ruled with lines varying from 50 to 400 to the inch: the
lower rulings give very coarse reproductions, and are only used for
posters, whilst the higher rulings yield very fine impressions and are
employed only for the best work. It is hardly necessary to remark that
the finer the screen the better must be the skill of the printer.
To illustrate the difference in the results obtained by the use of
different screens, the two figures on Plate 6 have been prepared; both
were made from the same negative, but for the upper figure a 100-line
screen was used, and for the lower a 200-line screen. It will be
observed that there is more contrast in the former, and more detail
in the latter. Authors should therefore mention when sending in their
original pictures the qualities they require in the reproduction; it
must, however, be remembered that the blocks made from the finer ruled
screens will not print satisfactorily except on more or less highly
glazed paper, to the use of the "art" varieties of which there are
objections on aesthetic and other grounds.

[Illustration: PLATE 6. Half Tone reproduction of a photograph by Mr.
W. Rowan.

Part of a shingle beach shewing plants of Sea Blite (_Suaeda
fruticosa_) and a ring plover's nest with four eggs.]

Before passing on it may be mentioned that screens with patterns other
than that represented in Fig. 4 are sometimes employed; for instance,
the wavy-line screen gives the impression of coarse collotype.

The preparation of the blocks may now be briefly dealt with.

A negative of the picture, using a screen suitable for the purpose,
is taken on a special dry gelatine plate ("process" plates) or on some
other form of negative, _e.g._, wet collodion which is most commonly
employed. This negative requires very careful development in order to
get the dots right.

From the negative a positive is made upon a copper or zinc plate,
suitably coated with a sensitive film. The usual practice is to coat
the polished metal plate with a mixture of water, albumen, fish glue,
ammonium bichromate, chromic acid and ammonia; the plate is then dried
and, when cooled, exposed under the negative. The action of the light
on such a film, the essentials of which are the albumen, the glue
or gelatine and a chromate, has already been described. The mixture
becomes more or less insoluble in water, according to the intensity of
the light falling upon it.

The positive is now rinsed in water, and is sometimes stained with
an aniline dye in order to render the film more visible. Next it
is developed in a stream of water until the surface of the metal is
visible between the dots, the last traces of the soluble gelatine
being removed with warm water. After drying, the plate is evenly
heated over a Bunsen burner until the dots of gelatine mixture turn
chocolate colour, when the plate is allowed to cool gradually. This
is known as burning in. The plate, if necessary, is now touched up and
the back, sides and margins varnished in order to protect them from
the acid: when the varnish is dry, the plate is etched in a weak
solution (about 2-1/2 per cent.) of nitric acid if the metal be zinc;
if the plate be copper, it is usually etched with a solution of iron
perchloride.

On taking a proof, there is almost certain to be a lack of contrast,
the plate is then fine etched, by which means a considerable
improvement can be made; and, by covering certain parts with an
acid-resisting substance ("stopping out"), it is possible to fine etch
locally.

Incidentally it may be mentioned that machine etching, by which a fine
spray of the etching fluid is distributed over the plate, has recently
come into vogue, for it is claimed that the results print better and
are in other ways an improvement upon the older method.

The plate may now pass through the hands of an engraver, who removes
any blemishes, as far as is possible, improves the high lights, and so
on; in fact, a skilful engraver can improve the plate considerably.

After the plate is trimmed, and the superfluous metal cut out by means
of a routing machine, it is firmly tacked to a wooden mount, usually
of oak, but sometimes of mahogany, especially if the plate is large.
In order to obtain the best results, the printing, in a typographical
machine, should be done on highly calendered paper--so-called "art"
paper; in fact, this is absolutely essential if a fine screen has been
used; it is only the blocks made with the coarser screens that will
give fair prints on ordinary paper. For this reason reproductions made
by the half-tone process are very generally treated as plates unless
the glazed paper is used throughout the book. The process is used
principally for the reproduction of photographs, and for pencil or
wash drawings.

With regard to photographs, it has already been mentioned that authors
should send the negative or two or three prints differently toned,
in order that the operator can choose the one most likely to give the
best result.

It is sometimes difficult in a photograph of a landscape to obtain
a negative in which the particular feature it is desired to
represent--_e.g._, in photographs of vegetation--stands out with the
requisite contrast. This is due to the position of the sun at the
time of exposure, or to the use of ordinary plates. The remedy for the
first is to take the photograph when the proper light obtains; with
regard to the second, the use of colour correct plates, together with
a colour screen in front of the lens, will obviate the defect. Since
for scientific purposes the correct interpretation of the various
tones of the vegetation, for example, may not be essential, variously
coloured screens may be used in order to emphasise a particular
feature. For instance, it will be noticed how well the bushes in Plate
7 stand out. This effect was obtained by the use of a panchromatic
plate in conjunction with a red colour screen.

[Illustration: PLATE 7.--Half Tone reproduction of a photograph taken
by Dr. Mees through a red screen.]

With regard to drawings in wash, charcoal or pencil, in which
there are half-tones; these are better drawn on an enlarged scale,
especially if the author is not a skilled draughtsman, for improper
gradations in shading and other imperfections will not appear so
noticeable in the reduced reproduction. Originals should all be
made in one colour; in the case of wash drawings, diluted Indian ink
(really Chinese ink) will give excellent results.

In making pencil drawings, a fairly stout hand-made paper with not too
much grain should be used. If the drawing is to be of some size, the
paper may be damped and pasted by its edges on to the drawing board,
it will then be stretched quite flat and will not cockle when dry.

The outline of the object may first be sketched in lightly with a
soft pencil and then the shading may be proceeded with. To do this,
broad-pointed soft pencils, 2 B, 3 B, or 4 B, should be used, and it
is better generally to work from the high lights to the shadows. To
avoid rubbing finished parts, the work should proceed from the top of
the board downwards, especially in the case of large drawings.

In order to obtain a nice gradation and a more smooth appearance--more
especially when a very coarse paper has been used--the work may be
gone over with paper stumps of appropriate size and softness, and, of
course, India rubber may be employed where it is desired to reduce the
density of the shading.

When finished, the edges of the various parts may appear woolly owing
to the rubbing of the lead; this may be cured by cleaning up the edges
with a trimmed piece of India rubber, but in so doing there is always
a risk of rubbing out part of the shading, especially if the outline
be at all intricate. If preferred, all the shaded parts may be fixed
by painting them over with a suitable solution, gelatine for instance,
paying particular attention in following the correct outline. When
dry, the application of soft india-rubber will soon clean up the
blurred edges.

If charcoal be used the same procedure may be followed. Charcoal and
pencil drawings should be fixed, in order to prevent rubbing, before
sending to the block makers. A suitable fixative may be purchased or
one may be made by dissolving white resin in alcohol and applying it
to the paper by means of a scent spray or an atomizer. A very good
fixative may be made by dissolving a little gelatine in hot water and
applying it whilst hot by means of a broad, flat camel hair brush,
or ordinary milk may be used in a similar way. After the fixative has
been put on, the drawing should be pinned up by one corner--unless,
of course, it was pinned up before the fixative was employed, which is
the best way when the fixative is an alcoholic solution--and allowed
to dry; it may then be placed under pressure in order to flatten it,
for fixed drawings generally shew a tendency to curl, especially when
the preparation used for fixing has only been applied to one surface
of the paper.


In making drawings for reproduction by means of the half-tone process,
there are a few general points to which attention should be paid.

It should be remembered that there is not infrequently a tendency
towards flatness in the reproduction; it is therefore important that
the originals should be "plucky," and, on the whole, it is better to
exaggerate with regard to high light and shade, especially if there is
much modelling or perspective.

Finally, with regard to lighting, it is better for the majority in
drawing their objects--solid objects in relief are referred to--to
use a more or less lateral illumination and to represent only the
high lights, shades and shadows referable to this main direction of
illumination. A high relief will thus be obtained, and the effect
will prove more satisfactory than if minor sources of illumination
are unsuccessfully dealt with. This is especially important in drawing
complicated structures such as models of vascular tissues, embryos,
etc.

In cases where many such figures are to occur on one page, it is
highly desirable that the lighting of each should be from the same
direction.

The use of the half-tone block is now almost universal, so that it is
hardly necessary to mention examples, more especially as they are hard
to judge without seeing the original picture. Those in the present
book are all of a high quality. Excellent examples will also be found
in Tansley's _Types of British Vegetation_ (Cambridge, 1911) and in
the _Journal of the Royal Horticultural Society_.


Proofs should be carefully compared with the originals, particular
attention being paid to the rendering of the tones; as already
remarked, fine etching will clear up a block and will often prove a
remedy to flatness.

An author will naturally consider whether a photograph is to be
reproduced by means of photogravure, collotype or half-tone. It is
impossible to lay down any laws on the subject, but the following
points should be considered.

If it is essential to have the reproduction in the text, a half-tone
block must be used; it must, however, be remembered that the paper
used for the letterpress may be very unsuited for the printing of
half-tones. On the other hand, if it be immaterial where the picture
is placed, then the relative merits of photogravure, collotype and
kindred processes and half-tone must be weighed.

Provided that expense need not be considered, photogravure will, in
the majority of cases, give the best results; on the other hand, if
this process is too costly, then the choice lies between collotype
and half-tone. The latter method will often give a result with more
contrast as compared with collotype, whilst collotype will give a
truer interpretation of the tones.

As has already been remarked, the best results with half-tone blocks
only are to be obtained by the employment of a paper which
seemingly has no lasting qualities; it therefore follows that if
the reproduction forms an important record, the use of collotype is
indicated, since many varieties of good paper are available. As a
general rule photo-micrographs are best reproduced by collotype.

In order that the respective qualities of these three
processes--photogravure, collotype and half-tone--may be compared,
Plates 8, 9, and 10 have been made from the same photograph, a view
taken by Dr. F. F. Blackman of the Bouche d'Erquy, a salt marsh in
Brittany, which was selected chiefly on account of the large number of
tones it contains.

[Illustration: PLATE 8. Photogravure]

[Illustration: PLATE 9. Collotype]

[Illustration: PLATE 10. Half Tone]

These three plates are not entirely comparable, since the heavy
shadows in the right hand bottom portion of the photogravure have been
touched up by the engraver. This was not intended by the author, but
the plate was retained as it shews that directions regarding this
point should not be omitted when sending the drawing or photograph to
be reproduced. It also indicates that for critical work, when an exact
a facsimile as possible is required, collotype should be used, for the
plate cannot be touched up.

With regard to the reproduction of drawings shaded by means of wash
or pencil, the same remarks apply, with the addition that if it be
possible to express what is desired by other means, suitable for
reproduction by line block, these latter should be employed. To
illustrate this point, Figures 5, 6, and Plate 11 have been inserted;
all illustrate the vascular skeleton of a fern (_Marattia fraxinea_),
the first one is in outline and the second is shaded by lines of
varying thickness; both of these are reproduced by means of the
line block, whilst the third is a reproduction by half-tone of a
pencil-shaded drawing. In order to obtain a fair comparison, the
half-tone is reproduced as a plate, owing to the fact that it would
not print satisfactorily on the paper used for the letterpress.

[Illustration: Fig. 5]

[Illustration: Fig. 6]

[Illustration: PLATE 11]


THE HALF-TONE THREE COLOUR PROCESS.--This process is much used for
colour reproductions of various subjects; and, in view of the fact
that the best results can only be obtained by the best photography,
the object should, if possible, be sent to specialists for
reproduction. In many cases, however, this is impossible, _e.g._,
landscapes and animal and plant portraits amidst their natural
surroundings, so that the scientist, if unable to make a water colour
drawing, which will give by far the best result, must make his own
negatives.

The first thing to do is to purchase a set of colour-filters, adapted
to the colour-correct plates to be used, from firms who specialize in
these matters, Messrs. Paget or Messrs. Wratten for instance, and
from them the inexperienced should obtain full information regarding
exposure, etc., for it is essential that the exposure of the negatives
should be correlated in order that all may have the same tone-value.

The colour-screens, blue, green and orange, are made by dyeing
gelatine with suitable stains; the films are stuck on to perfectly
plane glass and are mounted in frames. In practice these screens are
usually placed behind the lens, in which case a special camera is
necessary, or they may be adapted to fit on to the front of the lens.
In either case the procedure is the same; three negatives are taken
one after the other through each colour filter, the exposure being
modified in order that the tones in each case may be of equal value.

There are thus obtained three negatives which, of course, yield
positives which look very different one from the other. These prints
may be sent to the block makers, but it is better, on the whole, to
send the negatives with clear indications as to the colour of each.

From each negative there is made by contact a transparency, and from
these positives there are prepared a set of half-tone negatives from
which are made the half-tone blocks.

The reproductions are made by superposed printing of the three blocks,
yellow being printed first, then red, and finally blue (Plate 12).

[Illustration: PLATE 12.--Three Colour Half Tone.]

As indicated above, it is hardly worth while to make negatives for
this process unless the operator is a really skilful or at least an
efficient photographer, and even then the final product may prove
unsatisfactory.

Better results are generally to be obtained by sending to the block
maker a Lumiere colour photograph with full instructions regarding any
corrections in the colours which may be necessary.

Examples:--

Bateson: _Mendel's Principles of Heredity_, Cambridge, 1909. Church:
_Types of Floral Mechanism_, Oxford, 1908. Seward: _Darwin and Modern
Science_, Cambridge, 1909.

PHOTO-MECHANICAL LINE BLOCKS.--The photo-mechanical line block,
commonly known as a zinco, is in a sense the lineal descendant of
the wood block. As a means of reproduction the possibilities of line
blocks are very great, for not only is it possible to reproduce by
their means all kinds of line drawings, but also drawings in charcoal
and crayon, provided they be suitably executed on a proper grained
surface. In fact, an artist or draughtsman who has a thorough
knowledge of the process and its capabilities can obtain extraordinary
results. The process has the further advantage of being both quick
and inexpensive, a few hours only being required to make the finished
product.

Their mode of manufacture is the same in principle as for half-tone
blocks; in the case of the latter, the method known as the enamel
process was described; in the present instance a different procedure
may be dealt with.

A photograph of the drawing is taken on a negative, the wet collodion
process being generally followed, although dry process plates may be
used.

A highly polished zinc plate is sensitised with bichromate of potash
and gelatine, or by other means, and, when dry, is exposed under the
negative.

The exposed metal plate is then taken into the dark room and evenly,
but thinly, coated with etching ink. When the ink is dry, the plate is
developed in water; the unexposed gelatine, and with it, the ink, will
come away, its removal being helped by the judicious application of a
dabber of wet cotton wool.

The plate may next be "rolled over" with an ink which will more
stoutly resist the action of the acid than that used in the first
inking, but prior to this it is usual to soak the plate in a mixture
of gallic acid, phosphoric acid and gum. This second rolling up must
be carried out as if the plate were for lithographic reproduction;
and, when dry, powdered resin may be applied, in order to make a
better acid-resist, as in the preparation of a lithographic stone.

The plate is now etched slightly in a weak solution of nitric acid; it
is then rinsed, dabbed dry and placed upon a hot plate until the resin
has stuck well to the ink. When cool, the margins, sides and back are
protected from the action of the acid by means of a varnish and the
plate is given its first real etch, which is a very slight one. After
rinsing and drying, the plate is again heated until the ink and resin
have melted and flowed down the exposed sides of the ridges of metal
produced in the first etching. This application of ink and resin must
be repeated in order that the exposed sides of the ridges may be well
covered with the acid-resist and so will not be undercut. The plate
is then given its second etch, and this is done with a stronger acid,
after which the sides of the lines are again protected with resinous
material in the same way as before. The third etch follows, after
which the metal is thoroughly cleansed from all the ink, etc.

In order to smooth the shoulders of the lines, the plate is given a
finishing etch: the cleaned plate is warmed and rolled up with hard
etching ink; the metal is then heated until the ink becomes glazed,
and, when cool, is placed in the acid bath for the requisite amount
of time. If necessary the plate, after cleaning, is touched up with a
graver, and the superfluous metal is cut away. Finally it is mounted
on a block of wood, and after the corners and sides have been trimmed
square, the block is ready for the press.

To illustrate the enormous improvement which may result from the block
passing through the hands of a skilful engraver, two line blocks of a
wood engraving by Riocreux (see p. 36) have been prepared. Fig. 7 is
the impression given by the block as ordinarily turned out, whilst
Fig. 8 is a precisely similar block which has been worked up by an
engraver.

[Illustration: Fig. 7]

[Illustration: Fig. 8]

There are several other methods of making the blocks, but the
principles are the same as in the foregoing process.

In examining the proofs it must be remembered that deletions are not
the only alterations that can be made in the finished block; not only
can lines be cut away, or their character altered by removing part
of the metal from them, but additions can be made in reason. For
instance, lines can be added across open spaces, and if part of the
printing surface has been accidentally removed in cutting away the
superfluous metal, the damage can be made good by building up with
solder and working on this with the graver. If, however, the additions
required are at all extensive or complicated, it is better to have a
new block made.

Inasmuch as scientific illustrations are to describe and explain
definite facts, the drawings must needs be materialistic rather than
suggestive; in other words, a more or less conventional system must be
employed.

In making their drawings for reproduction by line blocks, authors have
at their disposal the black line, the white line, the black space,
the white space, the black dot and the white dot, all of which may be
combined in various ways. No tones, other than black and white, are
available; if it be desired to represent half-tones, they must be
rendered by the above-mentioned means.

In the majority of cases the originals should be made with black ink
on white Bristol board or smooth white paper; ordinary lead pencil
drawings on smooth paper are useless, and lead pencil, black crayon
or charcoal in combination with grained paper or board should not
be employed unless the draughtsman has the requisite skill and knows
exactly the limitations of the line block. For all ordinary folk black
ink and Bristol board cannot be improved upon.

The drawing may be made first with a soft lead pencil, using the
camera lucida or other optical aids to correct delineation. The pencil
lines are then gone over with ink; for this purpose a good black
ink is necessary. Wolff's Indian ink, Higgins' waterproof ink and
Steuber's waterproof drawing ink are highly satisfactory, and
there are many others. With regard to pens, a suitable implement is
all-important; Gillott's lithographic pens and Brandauer's No. 515 are
recommended. For straight lines of an even thickness a ruling pen is
very useful, and these may be obtained fitted with an adjustment which
enables the worker to rule a line of a definite thickness, _e.g._, .5
mm. and so on.

All drawings should be made larger than it is intended the
reproduction to be, for slight inaccuracies, ragged lines, and other
blemishes will thus appear less obvious. This drawing on a large scale
is often a stumbling block, because the work appears too open and the
draughtsman is tempted to put in too much; this must be avoided, else
the crowded lines may join together in the reduced reproduction. Also
it must be remembered not to draw too finely, else the work in parts
may disappear entirely in the reproduction. In drawing on an enlarged
scale a certain amount of exaggeration may be employed, in order that
when reduced the drawing may not be quite spiritless.

When representing a solid object, such as a plant or an animal, to
shew the external morphology, it is to be borne in mind that form
is the main thing to represent, and this can be expressed by outline
drawing alone. In fact, more or less primitive methods must be
employed, and better models cannot be followed than the best wood
cuts.

[Illustration: Fig. 9. The Lesser Celandine (_Ranunculus Ficaria_). By
R. G. Hatton. (From Hatton's _Craftsman's Handbook_).]

[Illustration: Fig. 10. The Lesser Celandine. After Fuchs. (From
Hatton's _Craftsman's Handbook_.)]

An examination of figures 10 and 12 will shew that Fuchs[A] attained
his object by simple outline drawings; he never employed local colour,
and shading he used very sparsely indeed, and then only to give
expression to the form of some thick part. Fuchs's celandine (Fig. 10)
should be compared with the drawing of the same plant (Fig. 9) by R.
G. Hatton.

    [Footnote A: The methods followed by the illustrators of
    the Herbals may be conveniently studied in Hatton's "The
    Craftsman's Plant Book," London, 1909, and Arber's "Herbals,"
    Cambridge, 1912.]

[Illustration: Fig. 11. The Apple (_Pyrus Malus_). After Matthiolus.
(From Hatton's _Craftsman's Handbook_).]

The methods of Matthiolus (Figs. 11 and 13) were somewhat more
advanced, for he used shading not only to express form but also to
give a certain amount of relief. It will be noticed that he shaded by
lines which followed the moulding of the parts.

The work of Riocreux (Fig. 8) should also be studied; it will be
observed that he managed to get a very high relief in his drawings by
the simple means of straight or curved lines, according to the shape
of the part, of varying thicknesses.

[Illustration: Fig. 12. Charlock (_Brassica Sinapis_). After Fuchs.
(From Hatton's _Craftsman's Handbook_)]

There is no necessity for keeping all the lines of even thickness.
For instance, provided the character of the form is not altered, the
outline on the shaded side may be made thicker than on the illuminated
side; also distance can be indicated by the use of thinner lines, for
these, although really black, will give the impression of greyness.
Then again, a line may be drawn with local increases and decreases in
thickness, as in ordinary writing, and such lines drawn by a skilled
hand can be made to express a marvellous amount of modelling.

[Illustration: Fig. 13. Sea Lavender (_Statice Limonium_). After
Matthiolus.

(From Hatton's _Craftsman's Handbook_.)]

The draughtsman, however, is not restricted to lines; any marks which
can be made with a pen and black ink may be employed, provided they be
sufficiently firm and large.

The accompanying figure (14) which is a reduction of an illustration
in Church's _Floral Mechanisms_, illustrates the use of lines of
varying lengths for shading.

[Illustration: Fig. 14. _Viola odorata_: Floral morphology. A
reduction of a figure in Church's _Floral Mechanisms_.]

In shading, the effect of shadow may be obtained by increasing
the thickness of the lines, but they must not be drawn too closely
together; on the other hand, the lighter parts can be represented by
thinner lines placed further and further apart, and the lightest parts
by the white of the paper. Cross hatching may also be employed (see
Fig. 15), but the crossed lines must not be too close together, for
otherwise they will tend to thicken in the making of the block and so
will print too black.

[Illustration: Fig. 15. A Seedling of _Abronia villosa_.]

For very delicate shading and tinting, stipple may be employed,
but the dots must be quite definite, sufficiently large to stand
reduction, and not too close together (Figs. 18, 28c, and 32). A
particularly good example of this method will be found in Butler's
paper on _Allomyces_ in the Annals of Botany, 1911, vol. 25. Dots have
also been employed in Fig. 28c (p. 69).

With regard to local colour; this may be indicated by shading, by a
white space, or by a black space.

Hitherto, drawing with black ink on white paper alone has been
considered, but the reverse is equally available; much can be
expressed by drawing with white ink on black paper.

Drawing in white upon a black ground is not frequently attempted, but
an excellent example by Miss Janet Robertson is shewn in figure 16,
which is well worthy of study, since it illustrates to a nicety some
of the means at the disposal of the draughtsman for line blocks. The
black surface is best obtained by the use of a waterproof Indian ink
applied with a brush to a white surface, the drawing being made with a
dense white ink, using a pen or a brush. The white ink may be made by
diluting any good opaque white water-colour paint, or process white
may be used. The composition of this should be zinc oxide or baryta,
for these do not darken with age; the author once used for this
purpose a white pigment which proved excellent at the time; the
drawings, however, subsequently turned dark brown owing to the fact
that the basis of the paint was apparently a compound of silver.

[Illustration: Fig. 16. _Neuropteris Heterophylla_.

A line reproduction of a drawing by Miss Janet Robertson.]

The top part of the drawing (Fig. 16), shewing the general morphology
of the plant, was drawn with a brush charged with white ink upon a
black ground. In the simplest possible way relief has been obtained by
representing the leaflets of the nearer fronds by white spaces, whilst
those further away are represented by white outlines. An enlargement
of a frond is shewn on the lower part of the picture, and here the
parts are represented in black on a white ground. The leaflets are in
black outline and the fruits are made to stand out, as in the upper
part, by the use of local colour--in this instance black--their shape
being indicated by the curve of the higher lights. In brief, a very
effective drawing has been made by the simplest use of the white line,
the white space, the black line and the black space.

[Illustration: Fig. 17. _Fucus volubilis_, var. _Flexuosus_, a
seaweed.

(From a drawing by Miss Baker.)]

This may be compared with figure 17, which was drawn by Miss Baker;
the method pursued is entirely different to the last, it being a pure
pen and ink drawing on white paper. No local colour has been employed,
and the modelling has been expressed by the lines used for shading
which have been made by short strokes with a fine pen. The result
is suggestive of an engraving but this was not intentional; under no
circumstances should an attempt be made to imitate in a relief block
effects which can only be obtained by intaglio.

From what has been said it is obvious that the photo-mechanical line
block can be used for the reproduction of all kinds of drawings in
pure black and white; to illustrate this figures 18-26 have been
inserted.

[Illustration: Fig. 18. The Larkspur (_Delphinium ajacis_). By R. G.
Hatton. (Hatton, _Craftsman's Handbook_.)]

[Illustration: Fig. 19. Hollyhock (_Althaea rosea_). By R. G. Hatton.
(Hatton, _Craftsman's Handbook_.)]

[Illustration: Fig. 20. A Liverwort (_Lepidozia reptans_). (Evans,
_Annals of Botany_, 1912, vol. 26.)]

[Illustration: Fig. 21. A Seedling of _Bruguiera gymnorhiza_, a
mangrove. Drawn by Mrs. F. E. Fritsch. (Tansley and Fritsch, _New
Phytologist_, 1905, vol. 4.)]

[Illustration: Fig. 22

A diagrammatic sketch by Mrs. F. E. Fritsch of _Rhizophora conjugata_,
a mangrove. (Tansley and Fritsch, _New Phytologist_, 1905, vol. 4.)]

[Illustration: Fig. 23

A shoot of _Acanthus ilicifolia_, a mangrove. Drawn by Mrs. F. E.
Fritsch. (Tansley and Fritsch, _New Phytologist_, 1905, vol. 4.)]

[Illustration: Fig. 24

A longitudinal section of a fossil seed, _Conostoma oblongum_. Drawn
by Dr. E. J. Salisbury. (Oliver and Salisbury, _Annals of Botany_,
1911, vol. 25.)]

[Illustration: Fig. 25

The Meadowsweet (_Spiraea ulmaria_), shewing four years' growth.
(Yapp, _Annals of Botany_, 1912, vol. 26.).]

[Illustration: Fig. 26. The Chesil Bank. (Oliver, _New Phytologist_,
1912, vol. 11.)]


THE DRAWING OF MICROSCOPIC DETAILS.

Questions relating to the drawing of microscope sections may now be
dealt with. Usually these are drawn in pencil and reproduced by means
of lithography; this is quite wrong, for in addition to its being an
unnecessary expense, it is also an inconvenience to a reader, since
the figures are necessarily divorced from the letterpress. There are
very few histological details which cannot be represented by line
blocks, and with a proper co-operation between the author, the
block maker, the printer and the publisher, even the delicacies of
karyokinesis could be reproduced in the text.

For demonstration purposes, transverse sections of plant-structures
may first be taken.

The walls of the various elements may be represented by lines of
more or less equal breadth, but in those cases where the walls are
particularly thick, _e.g._, the elements of the wood, the thickening
may be represented by an additional line. This is seen in Fig. 27, in
which it will be noticed that the middle lamellae of the wood-elements
are represented by black lines.

[Illustration: Fig. 27.

(From Butler's paper on Gummosis of _Prunus_ and _Citrus_. _Annals of
Botany_, 1911, Vol. 25).]

This is a particularly good drawing, but, unfortunately, it has been
over reduced.

On the other hand, the various tissues may be represented by lines
of varying breadths, the thickest walled cells having the same double
contour as in the above, but with the addition of local colour in
the shape of diagonal shading. This is not uncommonly found in
papers dealing with the anatomy of plants by French authors; it is
illustrated in Figure 28 _a_. If preferred, such thick-walled elements
may be entirely represented by thick black lines as in Figure 28_b_,
and when such cells are relatively few in number, this method has much
to recommend it since a greater relief is obtained.

[Illustration: Fig. 28

_a_

_b_

_c_

A transverse section to shew the vascular cylinder of the root of the
spinach, _c_ is somewhat older than _a_ and _b_.]

Finally, an attempt may be made to draw in a more detailed fashion
as in Figure 28_c_. Here the thickness of the cells of the wood is
represented by broad black lines, the middle lamellae being left white.
The lines marking the boundaries of the other cells vary slightly in
thickness, but this is to a great extent masked by the representation
of the cell contents, which consist entirely of dots in the case of
the protoplasm, whilst the nuclei are represented by dark ovals--black
relieved with small white areas. By varying the size of the dots and
their distance apart, varying densities can be indicated.

It has been mentioned above that it is possible to reproduce fine
detail by means of the line block; this is illustrated in Figs. 29 and
30.

[Illustration: Fig. 29]

Fig. 29, which illustrates a stage in the division of a nucleus,
was drawn with black crayon on a rough-grained piece of Whatman's
water-colour paper. The cytologist will, doubtless, criticize its
coarseness, but it may be mentioned that the roughest paper at hand
was designedly employed in order to illustrate the point raised. That
a finer grained paper will give more delicate results is shewn by Fig.
30, which is a reproduction of a drawing, kindly lent by Dr. W. G.
Ridewood, made with ordinary lead pencil on grained Bristol board. Its
delicacy is obvious, and at first sight it could easily be mistaken
for a lithograph.[A]

    [Footnote A: Many similar examples will be found in Ridewood's
    memoir _On the Cranial Osteology of the Clupeoid Fishes_,
    Proc. Zoo. Soc., Lond., 1904, vol. 11, p. 448.]

[Illustration: Fig. 30]

A half-tone can be put on to a line block during its manufacture. All
that the draughtsman has to do, is to indicate by blue pencil lines
those parts on which he requires the dots, which give the half-tone,
to be placed, and to select the pattern of the stipple he desires to
be used. The result may appear somewhat mechanical since the dots
are regularly arranged, but a drawing sometimes may be considerably
improved by this means if used with judgment. It is frequently
employed in representing drapery, and many examples may be found on
those pages of newspapers devoted to ladies' dress (Fig. 31; see also
Fig. 32).

[Illustration: Fig. 31. After a water-colour design by Miss Winifred
Pearse.]

THE DRAWING OF DIAGRAMS AND APPARATUS. Much valuable information may
be conveyed by diagrams; in fact, these could be used more freely than
they are.

[Illustration: Fig. 32]

The principles to be borne in mind are the same as for other ink
drawings. They should always be drawn upon an enlarged scale, and with
as little detail as possible, which generally should be indicated
in the most conventional ways--dots, black spaces, lines, and so on
(Figures 33 and 34). The main thing to be aimed at is clearness, so
that it is often necessary to sacrifice true relative proportions in
order to gain this end (Fig. 34).

[Illustration: Fig. 33. A diagram by Mr. E. Lee. (_Annals of Botany_,
1911, vol. 25.)]

[Illustration: Fig. 34

A Diagram from the _Annals of Botany_, 1912, Vol. 26.]

In certain cases it is possible to combine detail and diagram in one
drawing; this is shewn in Fig. 32, taken from Dr. Ridewood's admirably
illustrated memoir on the _Gills of Lamellibranchiata_ (Transactions
of the Royal Society of London, B. vol. 195, 1903). The shading
employed was either done by the draughtsman (at _ch_ and in the cells
with irregularly arranged dots), or else was put on the block during
its manufacture (_af_). If a lens be used, the difference will at once
be obvious.

The finished drawing should be bold and neat, and all lettering should
be very clear. If several figures are included in one diagram they may
be separated one from the other by ruled lines, and in no case should
one tier of figures--taking the frames as the boundaries--unevenly
overlap another tier, otherwise the diagram, to use an expressive
phrase, will look "like a pig with one ear."

Under the heading of diagrams must be included the representation of
apparatus. There are two ways of drawing apparatus; the objects may
be drawn as a study in still life, as, for example, in many of the
figures illustrating Deschanel's _Natural Philosophy_ (London, 1890)
or they may be represented in a purely conventional fashion. The
latter is the better way, and it is preferable to draw for the most
part in section in order that all connections, inlets, outlets, etc.,
may be clearly shewn.

A study of a good example is infinitely better than a written
description, wherefore Figure 35 has been inserted.

[Illustration: Fig. 35]

It will be observed that all glass vessels and tubing are represented
in section, and in the thermometers, the fine capillary bores are
represented by a single line in each case; corks by diagonal shading;
wood by lines in imitation of its grain; metal parts by vertical
shading or dead black; more or less still liquids by a series of lines
broken below and continuous at the surface, and gradually becoming
closer and closer together towards the surface. Mercury, on the other
hand, may be indicated by dead black relieved by a few white lines to
represent its reflecting surface, also its free surface may be drawn
convex. Finally thumb screws may be shewn by a combination of black
areas and vertical shading.

These conventionalities need not all be followed; for instance, rubber
connexions may be indicated by broad black lines and wood by diagonal
shading.

The drawing should be very bold and the different parts clearly and
freely indicated by writing or "printing."


THE DRAWING OF MAPS. In the drawing of maps for reproduction by the
line block process, if an existing map serves the purpose, a tracing
may be made in ink on translucent linen. If, on the other hand, the
author has to make his own map, the problem becomes more difficult.

For the obtaining of the data for map making information must be
sought for elsewhere, since we are only concerned in the preparation
of the map for publication. And as regards this, but few general rules
can be laid down since the character of maps is so diverse.

The amount of detail in the physical features represented depends to
a great extent upon the scale. Thus streams of a greater breadth than,
say, 10 feet, may in large scale maps be represented by double lines,
whilst no stream less than 2 feet in breadth will be shewn in low
scale maps.

[Illustration: Fig. 36

_a_ Contoured.

_b_ Spot-levels.

_c_ Layered.

These three figures illustrate in three different ways the varying
levels of a piece of ground surveyed by Prof. F. W. Oliver and Mr. A.
G. Tansley.]


The indication of hills is always a problem; the most satisfactory
way is by the drawing of contours (Figure 36_a_), and this whenever
possible should be followed, since it is scientifically the most
correct method, inasmuch as when properly drawn the form of the hill
is shewn exactly; further, contours obscure the detail to a much less
extent than does shading, and but little artistic talent is required
to draw them. If, however, contouring be impossible, the various
heights above the datum may be shewn by spot levels (Figure 36_b_)
or the relative levels may be shewn by layers; that is to say, by a
system of shading each kind of which indicates a certain level. Thus
dots may be used for all parts not more than 100 feet above sea level,
vertical lines for regions between 100 and 200 feet, horizontal lines
for parts between 200 and 300 feet, and so on (Figure 36_c_). It is
obvious that this method cannot be pursued if vegetation also is to be
shewn. The last choice is to represent the hill by shading in much the
same way as many of us did when children; the method referred to was
known as "herring bones" or "hairy caterpillars."

The sea or a broad expanse of water may be indicated by fine lines
which follow the coast-line and which may be placed at gradually
increasing distances apart.

If geological strata are to be represented, the accepted symbols
should be used; if the map is intended to represent the distribution
of soils, convenient signs may be employed, _e.g._, large dots for
shingle or gravels, small dots for sand, black areas for clay, and
so on; finally, if the distribution of plants or of animals is to be
shewn, symbols again may be employed. These, however, must be
quite simple and as far as possible give an idea of the organism
represented. This, in the case of animals, may be a difficulty, but,
with regard to plants, simple signs are easily inserted which give a
very good idea of the plant it is intended to represent. Many of the
signs used by the Ordnance Survey are ready to hand, and these can
often be used to designate plant associations.

The delimitation of areas should always be clearly shewn, and all
names should be very clearly "printed" indeed, and if they must be
placed on a dark portion of the map, they should have a good white
border around them.

The north should always be indicated. This may be done by drawing in
its proper position a representation of a compass or merely an arrow
pointing to the north. Unless otherwise stated, the arrow is assumed
to point to the magnetic north, and if no north be actually shewn it
is taken for granted by an intelligent reader that one of the vertical
sides is a true north and south line, with the north at the top.
Finally, under no circumstances should a scale be omitted--it is the
first thing a reader should look for.

For a map to look well two things are all-important, neatness and
clearness; both of these may nearly always be secured by drawing on
a large scale, bearing in mind what has been said about crowding
the detail, etc., and carefully considering how much reduction the
original can stand. This last point is of vital importance, for an
over-reduced map is an abomination; we have seen really good maps
absolutely ruined by this stupid error.

The inexperienced author should study the methods pursued by Prof.
Yapp in Figure 37. For comparison, the simpler way adopted by Mr.
Wilson may be studied (_Annals of Botany_, 1911, Vol. 25).

[Illustration: Figure 37. A Map of the Fenland by Prof. Yapp. (_New
Phytologist_, 1908, Vol. 7)]


GRAPHS OR CURVES. Simple though it be, the plotting of a curve for
reproduction requires thought and care. In the first instance, the
curve is drawn on squared paper, and the question naturally arises--To
what extent are the squares to be represented? If it be desired to
reproduce all the lines, say the paper is ruled in millimetres, a
half-tone may be employed, or all these lines can be ruled over in
black ink where the reproduction by line block is possible. It is,
however, seldom necessary to represent all the smallest squares; it
will generally be found that the centimetre squares are sufficient. If
the original be plotted on paper which is ruled in pale blue, it can
be reproduced by line block without re-drawing, since the blue will
photograph as white with the plates commonly used; all the essential
lines and curves must, of course, be in black. If, however, the
rulings of the squared paper are in red, yellow, or dark blue, a
tracing must be made. The horizontal and vertical sides should be
ruled with a broad black line, but the internal intersecting lines
should be much thinner. The actual curve may be in a continuous line
if one only be shewn on the graph; if more are drawn, then each must
be different, the obvious variations being the thick continuous line
---- the thin continuous line ----, dashes either thick or thin
---- ---- ----, dots . . . . . , and finally combinations of dots and
dashes ---- . ---- . ---- .

Owing to the difficulty which some experience in drawing freehand a
continuous line, the plot should be made twice the linear size of the
intended reproduction. A good rule to follow in drawing lines is to
keep the eye fixed on the point where the line is to end, the hand
will then guide the pen in the right path, especially after a little
practice. In many cases the ruler may be used, not only for straight
but also for curved lines, for good curve rules may be purchased.

In order that the figure may look neat, the lines should be of an
even thickness throughout their length; this is easily accomplished by
means of a ruling pen.


It has been stated above that Bristol board is the best material to
use for the making of drawings for line blocks; other materials may,
however, be employed, although they are not so nice to work upon.

For instance, it may be necessary to reproduce a map; this, as has
already been mentioned, may be conveniently done by pinning over the
map a sheet of pale blue tracing linen, and tracing the map on this
with Indian ink. The fact that the linen is blue does not matter, for
it will photograph as if it were white.

Then again, many subjects may be of so complicated a nature as to be
beyond the skill of the author to draw. In such a case a good plan
is to take a photograph of the object and make a positive on smooth
bromide paper, which need only be developed sufficiently far to give a
print which just shows the features. The print, when dry, can then be
worked on with fixed Indian ink. The finished drawing, when quite dry,
may be immersed in any solution which will dissolve out the silver; a
solution of iodine in potassium iodide answers sufficiently well. The
print will turn very dark, but it must be allowed to remain in the
bath until all the silver has dissolved; it is then removed, rinsed
under the tap and placed in an ordinary fixing bath of hyposulphite
of soda. All the colouration will be quickly removed so that the ink
drawing will stand out well against the white paper. All that it now
requires is a thorough washing in water; when dry it may be touched up
and then placed under pressure in order to make it quite flat.[A]

    [Footnote A: The chief disadvantage of iodine solution is its
    slowness of action; the following methods are much quicker.
    (_a_) To a solution of 4 oz. of hyposulphite of soda in
    one pint of water, add a 10 per cent. aqueous solution of
    potassium ferricyanide until the mixture is lemon coloured.
    When the silver image has quite disappeared, wash the print
    thoroughly in water. Since the mixture does not keep, the
    ferricyanide solution should be added to the hyposulphite
    solution immediately before use.

    (_b_) Mix 125 ccs. of a 10 per cent. alcoholic solution of
    iodine with 21 ccs. of a 10 per cent. aqueous solution of
    potassium cyanide, add to the mixture 1 litre of water.
    When the image has disappeared, which will be in less than a
    minute, wash for five minutes in water and dry.]

This method of drawing over photographic prints will often save
a considerable amount of time. For instance, it may be desired
to reproduce a consecutive series of drawings to illustrate the
microscopic structure of the subject. The ordinary way of doing this
is to make camera lucida drawings of the sections, which is a lengthy
and tiresome process; a photograph of each section will take much less
time and will give quite as good results.

Before sending any line drawings to press they should be carefully
examined; pencil marks may be rubbed out, lines touched up,
unnecessary lines removed by painting them out with white or black ink
according to the background, and, finally, a frame ruled around, if
necessary.

The amount of reduction, which should be marked clearly on the margin,
requires very careful consideration since under reduction may cause
the reproduction to appear too coarse whilst over-reduction may result
in the loss of the finer detail and the drawing may, moreover, appear
spiritless.

It must also be remembered that a reduction of, say, 1/2 linear means
that the reproduction will be a quarter the area of the original.

The best way to indicate the reduction required is to draw a vertical
or horizontal line, parallel to a side or the base of the picture,
of the exact length; or, the line may be roughly drawn and its length
indicated by figures thus ------------2-1/2"--------- .


The question arises as to when line drawings for reproduction by the
zinc block should be employed.

The answer is, Whenever possible.

The advantages to a reader of having the illustrations in the text
has already been commented upon. It is about the only method commonly
employed in which practically everything depends on the draughtsman;
the author thus exercises the greatest control. Finally the fact that
it is very inexpensive will appeal to editors and publishers.

As a matter of curiosity, the present writer picked out at random a
recent volume of a scientific journal to examine the illustrations;
although there were a number of text figures, an examination of the
plates--chiefly lithographs and collotypes--showed that there were a
large number of figures which ought to have been in the text. A more
detailed inspection of the plates was therefore made, with the result
that nearly 200 figures were found which with the minimum amount of
alteration--merely drawing in ink instead of pencil in the majority of
cases, and leaving out unnecessary shading in the others--could have
been reproduced by line blocks. If this had been done, a saving of
over 20 per cent. could have been effected on the plates. Some of this
would, of course, have been absorbed in the making of zincos, but
not much, since line blocks of excellent quality can be obtained for
2-1/2d. and 3d. per square inch. The above relates only to the most
obvious examples; the saving in plates would have been enormous if the
authors had drawn for the line process.


THE SWELLED GELATINE PROCESS. From the foregoing account of the
line-block it may, perhaps, be thought that a drawing shewing the
finest detail cannot be reproduced in the text by a relief block made
by photo-chemical means. This is not the case; the swelled gelatine
process is such that at its best the very finest work can be so
reproduced. The method is not extensively used, chiefly owing to the
remarkable amount of skill required to produce the best results and to
the facts that the blocks take longer to make and are more expensive
than the ordinary line block. This, however, should not militate
against its use, for the increased cost is but very little, and the
longer time in making, say two days, should not be of any consequence
in a monthly or quarterly periodical. The great point in its favour is
its great fidelity as compared with the ordinary photo-chemical relief
blocks: for instance, a close cross-hatching reproduced by a line
block will often come out as a series of white dots owing to the fact
that at the points of intersection the black lines tend to thicken;
hence, on printing, the white spaces, instead of being sharply cut and
diamond-shaped, are rounded. This will not occur in a good block made
by the swelled gelatine method. Further, the process does not restrict
the draughtsman to dead black ink; the drawings may be made in pencil,
crayon, or in ordinary writing ink: it is even claimed that wash
drawings and photographs can be reproduced satisfactorily by this
method. In the case of pencil drawings, the best results will be given
when the surface of the paper used by the draughtsman is slightly
rough; a pencil drawing on Bristol board, for example, will not be so
well reproduced as one on ordinary smooth drawing paper. In brief, the
process is as follows: a photographic negative of the drawing is made,
and under it is exposed a bichromate gelatine plate. This plate is
then developed in water. As already described, the gelatine will swell
up in proportion to the amount of light to which it was exposed. The
"positive" thus obtained will be in relief, the high lights being at a
higher level than the shadows. A wax mould of the gelatine positive
is then taken, covered with a thin layer of plumbago and electrically
covered with copper. The "casting" so obtained is built up with metal
and then mounted on wood in the same way as a zinco or a half-tone.
The capabilities of the process may be judged by a study of Fig. 38,
which is an extremely faithful reproduction of a lithograph, by S.
Prout, by the swelled gelatine process.

[Illustration: Fig. 38. A Lithograph by S. Prout reproduced by the
swelled gelatine process.]

[Illustration]




COST




RELATIVE COST OF BLOCKS AND PLATES


The question of cost is one of very great difficulty; in all
probability no two firms will agree in their quotations for different
kinds of work, and the reason for this lies in the large number of
factors involved, many of which are very difficult to compute exactly.
With respect to line engravings, etching, mezzotint, wood cuts and
wood engravings, it is impossible to give any idea of the cost. It
depends entirely on the complexity of the subject and the artist
employed.

As regards lithographic processes for reproduction in one colour the
cost varies with the nature of the work. If an artist be commissioned
to make an autolithograph, the fee would be agreed upon beforehand.
Photolithography and collotype, on the other hand, are processes
which do not require the hand of an artist, and these methods of
reproduction are relatively inexpensive. The price quoted by the
lithographer or collotyper is for printing so many copies, hence the
relative cost per copy depends upon the run and on the quality of
the paper used. Lithography is cheaper than collotype; but if several
illustrations are sent at the same time to be reproduced by collotype,
the cost for each would be less than if sent separately.

In chromolithography a separate stone is necessary for each colour,
hence the cost depends upon the number of stones used, and as several
may be necessary to obtain a first-rate reproduction, it is obvious
that the process may prove very expensive.

Turning to photomechanical processes, the prices vary according to the
grade of work required--the best possible, good, and, lastly, cheap
work. By best possible is meant the best that can be made under
existing conditions, the price being immaterial; in good work the cost
will be a limiting but not a preponderating factor, hence the work
will be open to criticism; finally, in cheap work, the price is all
important, so that the result is a block or a plate which will print
well but which must not be criticized as regards its being a faithful
reproduction of the original.

It is obvious that in the last two cases the quality of the work will
depend upon the agreed price, whilst in the first case the cost will
depend on the amount of time and skill required.

It is obvious, therefore, that a comparison of cost cannot be made
between these grades; it is, however, possible to draw up a scale of
relative cost of the processes under consideration for work of the
same grade. In the table given below, A represents the best possible
work, B indicates good work, and C stands for cheap work. Since the
line block is the least expensive it is taken as the unit of price;
that is to say, if a line block costs 3d. per square inch the cost of
half tone, three colour half tone and photogravure would be 7-1/4d.,
3s., and 1s. 2-1/2d. respectively.

                                           A       B       C
  Line                                     1       1       1
  Half tone and swelled gelatine           2-1/2   2-1/4   2
  Half tone three colour (three plates
      required)                            9       12      10-1/2
  Photogravure                             4-1/2   4-3/4   5

It must not be thought that if the area of a block is 3 square inches,
the cost will, therefore, be 9d. There is, for obvious reasons, a
minimum size at which the block or plate is charged although it may be
smaller. These minima vary; in general terms they may be taken as 12
inches for line, half tone and swelled gelatine blocks, and 20
inches for half tone three colour blocks and photogravure plates. The
measurements are the areas of the etched surface, the actual plate or
block may be larger, but for this margin no charge is made.

With regard to cost of printing, nothing need be said about blocks
which are set up with the type, namely line, swelled gelatine and
coarse half tone blocks. The price of printing fine half tones and
three colour blocks depends upon the quality of the paper used and
the fineness of the work. Photogravure plates must be hand printed
(photogravure printing on rotary machines is not considered here), and
skill is required; for ordinary printing on good plate paper the
price would be 10s. to 12s. 6d. per hundred copies, whilst for India
printing the cost would be about 25s. for the same number.




LITERATURE


  Barnes: _Illustrating Botanical Papers_, Botanical Gazette,
  Vol. 43, 1907.

  Bock: _Zincography_, London, 1910.

  Cumming: _Handbook of Lithography_, London, 1904.

  Cundall: _A Brief History of Wood-Engraving from its
  Invention_, London, 1895.

  Gamble: _Line Photo-engraving_, London, n.d.

  Hamerton: _Drawing and Engraving_, London, 1892.
            _Etching and Etchers_, London, 1880.
            _The Graphic Arts_, London, 1882.

  Pennell: _Lithography and Lithographers_, London.

  Richmond: _Grammar of Lithography_, London, 1909.

  Robertson: _The Art of Etching_, London, 1885.

  Verfasser: _The Half-tone Process_, London, n.d.

  Wilkinson: _Photo-mechanical Processes_, London, n.d.

       *       *       *       *       *




Transcriber's Note

Some extraneous Headings on otherwise blank pages have been removed.

Each Footnote has been indented and placed beneath the paragraph to
which it refers.

The Plates, which were on un-numbered pages, and some of the Figures,
have been moved to (usually) below the paragraphs which first refer to
them.

page 35: 'revelant' corrected to 'relevant' ... "See also the relevant
works cited under Literature"

page 90: The Table of Costings does not appear to make sense, but has
been left as in the original.

Hyphenation is not consistent in this book.









End of the Project Gutenberg EBook of The Essentials of Illustration, by
T. G. (Thomas George) Hill

*** 