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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.