The next step in this process will be to get a transparency of the subject. This may be made by any known process (at last, some one says we are getting away from the wet collodion) so long as it is clean, vigorous, and free from fog.
The transparency being at hand, that portion of it required to be transferred to the copper plate is carefully surrounded by a mask of tinfoil, or of non-actinic paper, which will serve as a safe edge to the carbon tissue to be used in making the negative resist, as well as to keep the margin of the plate free from extraneous picture.
This done, a piece of sensitive carbon tissue, a little smaller than the copper plate, which has been previously sensitized with bichromate of potash and dried, is placed upon the masked transparency and exposed to light until sufficiently printed; the tissue is then removed from the printing frame and placed in a dish of clean cold water; then one of the copper plates with aquatinted ground is also placed in the water, and the face of the tissue and the copper plate are brought in contact. After adjusting the tissue on the copper {126} plate, the two are withdrawn from the water, laid upon a bench, and a squeegee passed over the back of the tissue. Thus the driving away of the water from between the two surfaces will cause the tissue to adhere to the copper plate.
Now let the plate stand a few minutes, then immerse it in a dish of warm water at about 90° F. As soon as the tissue compound is melted, lift away the paper backing and throw it aside, then gently lave the copper plate with the warm water until all the soluble pigmented gelatine is dissolved; after that wash it under the tap, and place it in a strong solution of alum for fifteen minutes, and again wash and allow to dry.
When the gelatine image on the copper plate is quite dry, the margin outside the picture is coated with bitumen or spirit varnish, then the plate is placed in the etching bath of perchloride of iron (see page [121]), in which it is allowed to remain until the high lights under the thickest portions of the gelatine image just change color; then remove it and wash it under the tap; next clean off the resist image, and after drying and cleaning up, try a proof. If necessary, ink up as directed in Chapter I., page [121,] and rebite.
To succeed with this process it is only requisite to have a well-laid ground, a good, vigorous transparency, and the carbon tissue in good working order.
N. B.—In order not to confuse the above directions by interpolating the working details of carbon printing, these will be given in a chapter further on, together with formulæ for making suitable tissue.
CHAPTER IV. HALF-TONE INTAGLIOS. ELECTROTYPING METHODS.
The preceding methods of obtaining intaglio plates have been by the etching process. We now try another method whereby the printing plate is obtained by depositing a film of copper upon the photograph, and from this copper electrotype the prints are to be made.
There are many ways of proceeding to make these copper intaglios, the grain being obtained in many ways, but the foundation is the same in all, and consists of incorporating bichromated gelatine with grit of such a nature as to cause the image to be rough instead of smooth, or else the roughness is given to an ordinary or modified so-called carbon image developed upon a silvered copper plate.