CHAPTER V. Development of Negative Resist on the Copper Plate, and Preparation for Biting with Acid through the Gelatine.
Have a wooden box made 24 inches long, by 12 inches high, 12 inches wide, with door 6 inches high on side, fastened with hinges, top and bottom of box open; cover top with sheet zinc. Place inside Florence oil lamp; the door is valuable to regulate the heat. On top of box place deep porcelain tray, 11 × 14, fill with water half full; in the water place two pieces of plate glass ½ inch high and 4 inches long, on which to place copper to keep it from the bottom of the tray. Slide the copper plate into the water, removing all air bubbles, keeping the fingers off the surface of the plate. Take the sensitized and exposed tissue and place face down in the cold water (65 deg.) sliding it gradually in at further end of the paper so as to avoid air bubbles; the instant the paper curls backward, place it over the copper plate and remove it quickly from the water. This has to be done with celerity or it will be found difficult to mount the tissue with the squeegee on the copper, and also it should be exactly placed with reference to the top and sides of the copper; all this, of course, to be done under water, never allow it to slip up out of it. Place plate on table and squeegee into place, stroking firmly from the centre, each way. Place face down on clean blotting paper, under heavy weight for fifteen minutes. While plate is under pressure (which is necessary to enable the gelatine to expand and attach itself to the plate), start the lamp gradually, and by the time the paper is ready the water should register on the thermometer 75 deg. Slide the plate under water removing air bubbles as they appear, with a ball of absorbent cotton; when the heat of the water reaches 90 deg. Fahr., the gelatine commences to ooze from all around the edges of the paper, and after the plate has remained in the water about ten minutes after the showing up of the gelatine (at the temperature from 90 to 95 deg.), take a pin and carefully raise the paper at the corner, gradually pulling away the paper toward the opposite corner, keeping the hand close to the water; should the gelatine which adheres to the plate appear to lift, wait a few minutes longer and start another corner. After the paper is stripped from the plate, gently develop the negative resist with a piece of fresh absorbent cotton, delicately rubbing the surface, edges first, and lave the plate up and down in the water, keeping the temperature steadily at 90 to 95 deg., by raising or lowering the lamp. (Should the paper be under-exposed and appear very black on the copper, develop at 100 to 110 deg., not over. If over-exposed it will appear very thin, and the heat of the water must not go over 90 deg.; it will strip at 88 to 90 deg.) Then the negative image gradually appears, the darks first, which are of course the brightest portions; when all detail appears in the shadows and the negative stands out clear and bright, take it out of the dark-room (which is lighted with an ordinary lamp), and gently wash under the tap with clean and cold water at 65 to 70 deg.
Dry the resist with alcohol, pouring it over the plate from one end, starting with half alcohol and half water, gradually adding more alcohol and eliminating the water, until a final flooding with absolute alcohol is reached; use fresh solutions of alcohol and water for each copper; don't use old alcohol for anything except cleaning the copper at the end, and for removing the spirit varnish. Stand up to dry against the wall, face out, and standing square on the bottom of the plate, in the same position as you flooded it with alcohol; it will be dry in twenty minutes if rightly flooded. The bare copper should now be protected by a strong varnish in alcohol (it must flow freely off the brush); a good varnish for this purpose, and the best I know of, is an etcher's asphaltum stopping-out varnish, sold by Messrs. Devoe & Co., New York; price 50 cents per bottle. Should it get thick as you come to the bottom of the bottle, add a little spirits of lavender until it flows again freely. Take an architect's ruling pen and carefully rule a line with the varnish up to the edge of the picture, making it exactly true with the sides of the plate and the space on each side of the work the same with the top, the bottom space slightly larger; make sure that it slightly comes inside the picture. Keep the rule away from the surface of the gelatine, as it is very delicate. Then cover all the rest of the copper, protecting the bare parts and bevel, and bringing the varnish up to the line. Allow to dry hard; about twenty minutes will do. Form a wall about the resist, with walling wax, about an inch high; make a lip at one corner, the further left hand one, for instance; see that there are no leaks. There are several grades of wax, but Liedel & Co.'s is the best; when ordering you should give the name as modeling wax; gray is a good color. Pans can be used made of tin and varnished, or porcelain trays, protecting the back and edges of the plate with varnish, but I find the wax very helpful, especially on large plates.
