Into a tray pour 4 litres of water at 18° C., add 15 c.cm. nitric acid and mix well by shaking. Then place the prepared plate into the bath and rock it for seven or ten minutes (according to the fineness of the drawing), rinse well with water, remove the remaining water with blotting paper, and, finally, dry thoroughly with a fan. (Do not forget to dry the back.) Now warm the plate from the back, moving the flame about continually, so as to secure uniform heating and prevent warping of the zinc. The asphalt powder, which is as {81} yet but loosely attached, is more intimately connected with the subjacent ink through this heating process. The combination becomes evident from the assumption of a black lustre. With the appearance of this, stop heating, and lay the plate on a cold stone to cool. This done, spread some gallic acid over it with a soft sponge, and without washing it off, spread gum on the surface of the plate, and hasten the drying with a fan.
Mix some etching ink with varnish and work it out into a thin layer with good rough rollers. If the rollers are in order, wash the coat of gallic acid and gum from the plate, remove superfluous water and roll in (the manner similar to that used in lithography). The surface of the plate should not be more than moderately damp, so that the rollers may not slip. If a coat of color has been uniformly deposited, wash the plate with clean water, remove the excess with a sponge and blotter, dry by fan and remove all moisture by heating to 45° C. Dust the warm plate again with asphaltum (remove the excess), and warm it a trifle to secure better adherence. Strengthen the bath by the addition of 15 c.cm. nitric acid, and etch again for seven or ten minutes under continued shaking. Then rinse the plate, remove the water and dry with a fan, and burn in the resin powder well. Careful inspection will now show a successful and uniform but still weak relief.
As before, the plate is coated with gallic acid and solution of gum, is dried, washed, and blackened in, in which treatment one-third “wax pomatum”* is mixed with the etching ink. After washing and drying heat the plate up to 60° C., thus causing an imperceptible widening of the drawing. After coating dust once more with asphaltum, warm it and cover only the back and the white rim around the drawing with a solution of shellac (1 part ruby shellac in 10 parts spirits). Strengthen the bath with 20 c.cm. of acid and bathe it for seven to ten minutes, shaking the bath regularly. Continue until you see that the lateral action of the acid has almost wholly destroyed the lateral covering produced by heating. Do not, however, etch too long, and do not mistake the over-hanging coat for the other. Then follow washing, drying, melting on some resin, cooling, coating with gum, blacking in with equal parts of etching ink and “wax pomatum,” then washing, drying, greater heating (70° C.) (so that by increasing the ink each line receives lateral protection), cool and dust to excess with the finest resin dust. {82}
* Wax pomatum is prepared by cutting beeswax into fine parts and covering it in a wide-necked flask with oil of turpentine. In a few days a jelly-like mixture will remain, which serves the above purpose.
As we have now reached the necessary depth for the narrowest portions, we use, instead of the asphaltum, resin, which melts easily and spreads out readily, in order to attain protection for our middle etching.
Strengthen the bath with 30 c.cm. acid, and bathe until the lateral action of the acid has reduced the lateral coating to a narrow edge. Then wash, dry, melt on some resin, cool, prepare with gum. Blacken in as before, but employ one-third etching ink and two-thirds wax pomade and apply so thickly that all the narrowest spaces of the drawing are completely filled with color. Continue warming until the ink, which was applied, has well covered each line; then dry and use resin as before.
The acid may now be strengthened by 100–158 c.cm., according to the strength of coating chosen. Bathing must be continued until the edge that has run off begins to grow narrow. Wash, dry, burn in resin, cool, coat with gum, and blacken in by rollers with clean wax. Continue heating until each line is well covered by ink. Always dust until the ink is fully saturated and then heat gently.
Strengthen the bath 200 c.cm. and begin the deep etching. According to the depth to be attained repeat the manipulation of strengthening once or twice. Whenever a corrosion of the lateral coating becomes apparent, coat freshly, adhering to the above order of operation. For obtaining the necessary depth ink is applied about ten times, adding wax each time to facilitate the spreading when warming.
In order to attain a fine, regular lateral coating, great ability in manipulating the rollers is necessary, since without such the correct degree of strengthening is never attained. Irregular coating leads, of course, to irregular melting of the ink; one spot then is already sufficiently wide, while another is not yet covered. In such cases coating with a brush must be resorted to.
If the necessary depth is attained, the plate is to be freed carefully from the coating with a brush and oil of turpentine, and then placed in fresh sawdust, which absorbs the oil of turpentine and leaves behind a clean surface. Now the work can be criticised in all its parts. To every coating is a corresponding narrow edge of etching, which is now to be removed in order to make the plate fit for printing. To removing these edges we must devote our attention. We begin with the top one, and make preparations thus: Roll out on a clean, warm stone with faultlessly smooth rollers a very thin gauze-like layer of etching ink. Likewise warm the zinc plate and roll it in all directions without pressure till the picture becomes beautifully black. {83}