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.