The roller having a coat of rather moist ink spread evenly upon it, place the exposed zinc, face up, on a piece of clean white paper, and proceed to roll it briskly to and fro, using a moderate amount of pressure, until the whole of the turpentine has evaporated; it should leave a thin coat of ink with an even {47} matt surface, not thick enough to quite hide the yellow film of the sensitive albumen, as, if it does hide it, too much has been put on, and it will most likely smear in development.
If, after first applying the roller, the ink on the zinc seems likely to be too thick, at once wipe the roller dry, and then roll the zinc briskly until the coat of ink is perfectly even and the turpentine evaporated.
At this stage everything depends upon getting the coat of ink even. If there are patches of thick and patches of thin, sprinkle some turpentine upon the slab, quickly charge the roller, and roll up the zinc again, until the coat of ink is thin and even.
An even coat of ink being obtained, the zinc is laid in a tray containing clean cold water of a sufficient depth to well cover the surface. Now take a pledget of cotton-wool and rub the surface gently, when the ink covering the albumen protected from light by the black portions of the negative, will wash away, leaving the picture on the zinc in ink; if the finer details do not develop easily, continue the rubbing with the cotton-wool, but be careful not to rub so hard as to scratch the ink lines.
All details being developed, rinse the picture under the tap and put it away to dry, which at ordinary temperature will take but a few minutes.
The chances of failure in this portion of the process are, first of all, air bubbles and dust spots in the film. These will at once declare themselves. The remedy, is increased care and cleanliness.
If, upon development, some of the lines are missing, then the zinc and the negative have not been in actual contact, or if the finer lines wash away easily, then the exposure has not been long enough; whilst if it has been too long, either the finer details are covered up or the whole refuses to part with any ink.
A satisfactory print, showing all the lines of the original having been obtained, dry, by first blotting off the water, then by gentle heat, after which the zinc is ready for the etching room.
CHAPTER VI. PRINTING ON ZINC IN BITUMEN.
The process described in the previous chapter is most suitable for printing on zinc, for blocks that are not overburthened with fine lines, and is intended for rough printing; and also, when from want of sunlight, and the exigencies of business, the exposure has to be made by electric light; but when the subjects are very fine, and the blocks must be of the very best, it will be better to print the image in bitumen; then the first etching can be done without having to ink up previous to immersing in the acid bath (which must be done after developing the inked albumen image), so getting the sharpest possible results, and also securing better depth to close work than when the inking up has to be done before biting in.