Photo-engraving, Photo-etching and Photo-lithography in Line and Half-tone / Also Collotype and Heliotype

by W. T. Wilkinson

These results are obtained as follows: The prepared plate bearing the design is inked with a thick ink containing a little wax, and is placed in a trough with acidulated water, which slightly attacks the metal.

The trough is mounted so as to rock, and is kept in motion by a lever actuated by a steam motor. The water moves to and fro over the entire surface, and keeps continually washing the parts that are not protected against its action. No local saturation, therefore occurs, and the continuously renewed liquid attacks the bottom as well as the sides of the hollow. The sides would soon be rendered too thin were the biting-in too long continued, and for this reason the first attack is made with great care. It is upon this that depends the sharpness of the proof. The acid used is nitric, so dilute that it is scarcely perceptible to the taste, and in the proportion of about one and a half ounces to a quart of water. The acidity is kept up by a small quantity of acid of 36°, that falls drop by drop from a bottle provided with a cock. After about a quarter of an hour, the plate is taken out, and the operation repeated as generally directed.

Remember this: At every new biting-in the acidity of the bath is increased, and, when the broad parts alone remain exposed to the attack, acid of 6° B. may be used. In this state, the zinc plate, taken from the bath and washed and dried, is treated with benzine, and then with potash, in order to remove all fatty matter. It may then be seen that the sides of the hollows do not exhibit a regular sloping surface, but a series of ridges corresponding to the series of bitings-in. As these might take the ink, and affect the purity of the lights and shades, it is necessary to remove them by an operation analogous to the first, but carried on quickly in an opposite direction. With this intent, the plate, well cleaned and heated upon the iron table, is inked while hot, with a composition formed of two parts printing ink and one part each of resin and beeswax. This ink, which can be used hot only, descends along the sides of the depressions, and when it has got half way to the bottom the plate is cooled, and the inking is renewed so as to well cover the entire surface.

It must not be believed that in practice these operations can be conducted without extreme care. A want of attention, unsuitable ink, or a too high or low temperature, may lead to the loss or poor execution of the piece. It is often objected that the lines in this style of plates have not the boldness of those produced by the graver. It is not for us to answer the question whether this is a merit or a defect; artists generally endeavor to employ paper with an irregular and granular surface, and which is far from giving such boldness; {102} and he perhaps would be poorly appreciated who should present upon glazed paper a drawing made with the pen and resembling a picture made with the graver. It is the artist’s business to produce the work such as he desires the Gilloteur to render it.—GILLOT.

MULTIPLICATION OF ZINC ETCHINGS BY GALVANIC MEANS AND BY STEREOTYPING.

Multiplication of printing-blocks by galvanoplastic, or stereotyping, is not so easy as in case of woodcuts or type. The main difficulty lies in some peculiarities of the process of etching, especially if the plate has been produced by the French method. The reproduction of a form is often impossible, since the matrix is caught on certain rough spots and then tears, thus rendering galvanoplastic reproductions imperfect.

Having very frequent opportunity of making matrices from plates, I call the etcher’s attention to several points upon which the success of the work depends. On no condition whatever may any parts of the plate be corroded from beneath, as wax or gutta-percha will invariably tear when lifting off the impression (mould).

In the second place, the bottom of the etching must be perfectly smooth, not rough; the single grades, left by etching, must be removed, and the lines must incline perfectly smooth toward the depth of the etching.

In stereotyping, the process of drying presents special difficulties, since with heat the wood warps and distorts the plate; the cold process, on the other hand, does not give equally sharp impressions. For this purpose I have mounted the plates on lead instead of on wood, and am thus enabled to get sharp impressions and to apply hot drying.

Instead of paste, I employ light magnesia; instead of oiling the plate before planing or rolling it in, I give it a high polish with stearine oil and rouge by means of a circular brush, and brush it once more with talc. Thus I am sure of success.