_LINE PROCESS._
The methods of drawing for reproduction by, and in compliance with the
requirements of, a line process, are numerous and varied. They include
pen, pencil, and crayon, and modifications and combinations of all
three.
The information which I shall give is intended chiefly for such as know
little or nothing of the manner in which such illustrations should be
produced. Having already mastered the primary methods, the more
practised draughtsman, knowing what any special reproduction process
requires, will, to some extent, invent his own methods and often resort
to some "dodge" which may occur to him, thereby producing some
delightful and original result.
In describing the half-tone process we found the necessity of having an
image in relief of such a character that we could print from it in ink,
hence the intervention of a ruled screen, which broke up the flat even
tints of the original picture into minute dots. Line processes, as the
term implies, are used to reproduce an illustration which, as in a pen
and ink sketch, possesses no flat tints, and requires no screen, the
actual lines being reproduced in relief and printed in facsimile.
It will, of course, be remembered that a mechanical process block can
only produce in simple black and white: that is, it either reproduces a
line, to print black, or omits it altogether; so that a line drawn in
grey ink, and another in black, would each reproduce exactly the same,
namely black. Whereas in wash drawing we were limited to a few varying
tones, we are now restricted to two--white and black--and, as may be
seen by looking at any good line drawing, various degrees of shade are
produced by a multiplicity of lines in greater or less proximity and of
varying thickness.
Before proceeding further, I will give an outline of the three principal
processes used for producing drawing in line. These are the swelled
gelatine, the albumen, and the bitumen processes;--other processes exist
but are little practised, and offer no advantages over the above. The
albumen and bitumen methods are processes of etching on zinc and
familiarly known as "zinco" line process; not so the swelled gelatine,
as will be seen from the following description of it. Gelatine of a hard
variety is melted in water with the addition of a small quantity of
sugar and chrome-alum, and is then spread evenly upon a perfectly clean
glass plate. This gelatine film is, when required for use, sensitised by
immersion in a solution of bichromate of potassium, methylated spirits,
and water. The effect of this is to render the film, to some extent,
insoluble where acted upon by light; or, more correctly speaking,
non-absorbent when affected by light. A negative, made from the original
to be reproduced, is placed in contact with the sensitised film and
exposed to light. The film, which it will be remembered is resting upon
a glass plate, is then placed in cold water, with the result that those
parts which have been protected from light absorb water and swell up,
leaving the non-absorbent parts, which represent the image, sunk in.
When this operation has been carried far enough, a plaster of Paris cast
is taken, and from this a wax mould is made, which is practically a
duplicate of the gelatine mould from which the plaster cast was made.
Into the wax mould copper is deposited, precisely as in ordinary
electrotyping, thus giving us a copper relief from a gelatine or wax
mould made direct from the original.[2] This process, while a favourite
with the artist, is not so readily used by the process worker because it
is somewhat expensive, the average cost of a block being from 9d. to 1s.
6d. per inch. But the results are very fine, especially when a drawing
has been made in ignorance or regardless of the requirements of process
reproduction.
The zinc etching processes, by which the great mass of newspaper blocks
are made, are less regardful of delicacies of execution which the
swelled gelatine often reproduces with astonishing fidelity.[3]
In the albumen process the sensitive film is composed of egg albumen,
bichromate of ammonium or potassium, and water, which is spread upon a
_zinc_ plate. After exposure to light under the negative, the whole
surface is inked over with transfer ink, and then immersed in cold water
and gently rubbed. The ink will wash away from those portions which have
been protected from light by the opaque portions of the negative, and
will adhere to those affected by light. Thus on a bed of zinc we have an
ink image on a substratum of albumen, the exact copy of the original.
The zinc has now to be etched with acid.
With bitumen the procedure is somewhat similar. The bitumen is first
treated with ether, which will dissolve out only those constituents
which, not being sensitive to light, are not required. The residue is
dissolved in benzole and spread upon a zinc plate, as with the albumen
process. After exposure to light under the negative, the bitumen film is
washed with turpentine, which takes away all except those portions acted
upon by light. The film is next washed in water and placed in a very
weak solution of nitric acid, which at once attacks those portions of
the zinc unprotected by bitumen. If what now remains of the film be
inked over we shall have, as in the last process, an ink image of the
drawing on a zinc base, and the plate is now ready for etching.
The etching is performed by successive baths of diluted nitric acid, gum
and powdered resin being applied to the plate after each etching, and
heated so as to run down the sides of the ridges of metal (which at each
successive etching bath are gradually growing deeper) until the "biting"
or etching be considered deep enough. The ink and substratum of albumen
or bitumen are then cleaned off with American potash, and the plate is
finally washed. Rebiting, or still further etching, may be required
before the zinc relief is ready to be mounted on a wood block "type
high" for printing purposes.
As in the half-tone process, I do not pretend to have given working
instructions, but only such general particulars as may interest the
artist or draughtsman whose work is to be reproduced. For either of
these processes the average cost is 4d. to 6d. per square inch, with a
minimum charge of 5s. for a single block. Each process has its special
uses and applications; the process craftsman (whom nothing delights so
much as a sharp, brilliant line) will usually recommend the bitumen, but
the albumen method will often give a more pleasing result. As a general
rule, if your work is placed in good hands, the particular process to be
used is best left to them to decide, and if a proof be submitted some
little alterations may be suggested which can be carried out by an
engraver.
In the subsequent pages of this book I shall make little reference to
these processes; enough has been said, and they are no part of the
draughtsman's business, only it will be well to keep in mind throughout
such general particulars as have just been given.
Little has been said with reference to the negatives used in
reproduction; but as the draughtsman who also possesses some knowledge
of photography may be tempted to copy his work himself, it may be well
to point out that the negative image must be as sharp as it is possible
to get it. The most trifling deviation in focussing, unnoticeable in
ordinary photography, will tell seriously in making a reproduction;
moreover the kind of negative one may have learned to make for ordinary
photographic purposes will not do here. The function of the negative is,
it will be remembered, to protect certain portions of the film from
light, and to freely admit light where the image is, hence the denser
portions of the negative must be very nearly, if not absolutely, opaque,
and the image as nearly transparent as possible; thus giving what
photography proper has taught us to abhor--a black and white print. With
ordinary plates, the required amount of density is not always easy to
get, and special photo-mechanical plates are supplied by Mr. John
Carbutt, of Wayne Junction, Philadelphia, Pa., which give the desired
result. These plates are slow, thickly coated, and capable of giving
great density, all of which are characteristics peculiarly suitable to
the purpose. But in the end the process man will not thank you for
saving him the trouble of making a negative; he is accustomed to make
negatives of a certain kind, and very properly prefers to do this
himself.
Not the least contributory towards a good reproduction is the power
which reduction from the original places in our hands. When making the
copy negative it is most usual to make it much smaller, or, inversely,
the original drawing is made a good deal larger than it is required to
appear (See Illustration on page 72). A somewhat ragged line of (say)
one-eighth of an inch in width, would, if sufficiently reduced in size,
come out as a fine line no thicker than a hair. Though reduction carried
to such a degree would be impracticable, a drawing twelve inches by nine
inches, reduced to eight by six, will usually be advantageous. Not only
is a certain degree of coarseness and roughness thus removed, but the
lines themselves become smoother and rounder; lines, however, which are
very close together, are apt to close up into a solid mass, both from
the reduction and because lines sometimes have a tendency to thicken in
reproduction--a point to be guarded against when drawing.
If a drawing be examined through a simple double concave lens, that is
to say the reverse of a magnifying-glass, the effect of reproduction can
be seen, and the result anticipated; such lenses, called "diminishing
glasses," are sold expressly for the purpose.
The reader need hardly be reminded that everything on the drawing will
be reproduced, except perhaps _blue_ pencil lines, this colour being
photographically white; hence all finger-marks, spots, and stains must
be carefully avoided. No doubt these, and sundry faults in drawing, can
be cut away by the engraver, but an ideal block is one which requires no
such helps to perfection, but which comes from the etcher's hands ready
for use, and to such an ideal even the tyro must work.
The strong point and chief recommendation of a process block is that it
reproduces in _facsimile_ the draughtsman's original; once introduce
hand-work and it begins to lose this character; moreover expense and
delay in production are incurred, again depriving the mechanical block
of its distinctive and valuable features.
Sundry elemental methods of getting an image on to zinc for etching
without the intervention of photography may perhaps suggest themselves
to the reader. Thus, for instance, an outline drawing may be made in
transfer ink on transfer paper and at once laid down on the zinc and
etched. A glass plate, coated with a soft opaque substance, may have a
design scratched thereon and be used in place of a negative; but such
methods are crude and limited, and need not be considered here.
We will now pass to an examination of the various kinds of drawings
suitable for reproduction by relief process blocks, describing as nearly
as possible how they are made and with what materials.
[Illustration]