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.]