CHAPTER V.PRINTING ON THE ZINC IN ALBUMEN.
The negative being ready for printing, select a piece of zinc a little larger each way than the picture, polish, then grain, and after well washing it under the tap and gently rubbing it with a fine sponge, or a pledget of cotton-wool, place it in the whirler; again rinse under the tap, now invert the whirler and set it revolving; then examine the surface of the zinc and see that there is no dirt on the surface, but that it is quite smooth. If it is not, rinse it again under the tap, and rub it gently with the sponge, and again rinse. This should quite free the zinc from any deposit of dirt. Now whirl it so as to get rid of as much as possible of the water, then pour over the surface of the zinc sufficient to cover it, of the following solution (carefully filtered through cotton-wool):
Albumen of one Egg.Water7ounces.Saturated Solution of Bichromate of Potash1ounce.
Albumen of one Egg.Water7ounces.Saturated Solution of Bichromate of Potash1ounce.
Place the white of egg in a bottle containing a lot of small pieces of perfectly clean glass, then add the water and shake it well for a minute; then add the solution of bichromate and again shake it well. Now place a pledget of cotton-wool in the neck of a glass funnel, and pass a few ounces of clean water through (if this is not done, there will be difficulty in getting the albumen to filter); drain as much as possible of the water away, and then filter the albumen into a clean bottle; when all the solution has gone through, remove the cotton-wool from the funnel, which well wash, then recharge with a fresh pledget, pass some water through, and again filter the albumen solution through, this time into a ten ounce glass-measure, which is to be used for pouring from upon the zinc. The stem of the funnel should be long enough to reach the bottom of the glass measure, so that the formation of air-bubbles be avoided, which is impossible with albumen if the funnel is not below the surface of the filtrate.
Of this, pour over the zinc sufficient to well cover the surface, letting any surplus go into the sink; then set the whirler revolving, coat again, and{46}again whirl; now examine the surface, and if it is free from dust, spots, and air-bubbles, remove the zinc and dry it over the spirit stove. But if either air-bubbles or dust be present, wash them off under the tap, and begin again.
The film being dry, get the printing frame ready, see that the surface of the glass inside is quite clean and free from grit, as also the back of the negative, taking special care that the ridge of varnish which often forms at the bottom of the negative be removed, as the slightest inequality of surface will surely cause disaster directly the screws exert their pressure.
Do not lay the negative into the frame flat upon the glass, but slide it in from one side, so as to carry any dust away from the glass front of the printing frame.
The negative being in the frame, film side up, lay the coated zinc upon it, face down, judging the proper position and placing the zinc flat down upon the negative; now put a piece of brown paper over the back of the zinc, then place the back of the printing frame in place, fasten down the cross bars and apply the pressure screws, evenly and gently.
Do not screw one side tight before the other has been touched, but screw down so as to tighten all as evenly as possible.
Even pressure being applied, see that the front of the frame is clean, and then expose to direct sunlight for five minutes. Remove the frame to the dark-room, unfasten the cross bars and remove the zinc, taking great care to avoid scratching its film against the film of the negative.
After wiping the inking slab with clean linen place a piece of the transfer ink, about the size of a small bean, upon the upper corner, sprinkle this with a little turpentine, and mix them with the palette knife until they are of about the consistency of printing ink.
Now with the palette knife spread some of this mixture as far as possible over the inking slab, and then distribute it with the composition roller. Roll to and fro, across and diagonally, until there is a thin, even coating of ink all over the slab (not touching the corner where the ink was mixed with the turpentine) and upon the roller; if the mixture is too dry and refuses to spread, sprinkle on a little more turpentine, but do not use too much, else it will take a long time to evaporate.
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.