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

by W. T. Wilkinson

Whilst the gum is drying, with a palette knife place equal parts of transfer ink (page [44]) and of etching ink (page [54]) upon one corner of the inking slab, then thin to the consistency of cream, with middle varnish, thoroughly incorporating the three ingredients with the palette knife.

Now place a little of this ink upon the leather roller and roll vigorously upon the slab, so as to distribute the ink thoroughly upon both roller and slab; be careful not to get too much ink on the roller, nor to have it too thin; in fact, work the ink as stiff as is possible.

Now lay the zinc upon a piece of clean paper, and sponge it gently over with a wet sponge, so as to loosen the film of gum, then squeeze the sponge nearly dry, and pass it over the plate again, so as to insure it being evenly damp all over, but be careful not to make it too dry.

Now proceed to roll up, by passing the charged roller to and fro over the plate, using moderate pressure and slow motion, recharging the roller at short intervals from the inking slab. Occasionally use the damp sponge so as to keep the plate sufficiently damp to resist the ink.

If the roller slides instead of rolling, wipe it with an old linen rag, which will remove the moisture; then recharge the roller again upon the slab. {57}

The rolling is continued until the whole image is an intense black, when it is carefully dusted over with very finely powdered resin applied with a broad camel’s-hair brush, taking care that all the image gets covered. Then rub it gently with a wet, soft sponge and place it in the etching box containing a mixture of water and nitric acid, the acid being only just perceptible to the taste.

The plate should remain in this for one minute (the box being kept rocking); it is then removed, and thoroughly washed back and front under the tap. Rub it gently with a clean soft sponge.

This etching is merely to remove any traces of gum or dirt from the zinc which would interfere with the shellac varnish holding.

Now dry the plates, using gentle heat, then coat the back with thin shellac varnish to protect it from the acid; do the same to the margin of the picture on front, also varnish the centre of any very broad whites up to half an inch of the image, so that the acid dissolves no more zinc than is necessary. Now examine the image carefully, and if any of the lines are defective touch them up, and make any alterations and additions required.

The plate is now ready for the first etching, for which purpose a little nitric acid is added to the water in the etching tray—precise directions cannot be given as to how much acid to add, as so much depends upon the area of zinc on the plate that requires dissolving; practice, however, will soon enable the operator to judge the proper quantity. If too much acid is added, the plate will quickly be covered with myriads of minute bubbles, in which case it must be instantly removed, well washed, and the bath diluted with water before the plate is reimmersed. If, on the other hand, there is too little acid present, the action is too slow, and more must be added.