A Handbook of Illustration

by A. Horsley Hinton

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.