CHAPTER VII.
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]