Nitric acid may be replaced by sulphate of copper, especially in the first periods of etching, and etching can be obtained both in a galvanic way and by easy shaking of the tray. The sulphuric acid of the copper sulphate combines with the zinc and the copper, and when liberated, precipitates as an amorphous, muddy substance.
Although this process has almost entirely fallen into disuse, the most important points are treated of below.
The bath.—Dissolve pure copper sulphate (of the strength of 9° Beaumé) at a temperature of 15° C. Etch galvanically in this bath by placing in it a clean {104} copper dish. The plate prepared for etching as per page [84,] is rubbed bright at the four corners and four S-shaped narrow strips of sheet copper are so fastened to the bright zinc that the S-shaped end rises about three millimetres over the picture. Then place the plate face downward for three minutes into the bath, above the copper plate, which is electrically connected with the zinc by brass strips, so that instantly a strong galvanic current is set up. The etchings are found to be very satisfactory and interesting. In three periods (nine minutes) a beautiful preliminary etching is obtained with rather perpendicular faces.
I cannot recommend etching by shaking, as the sediment causes rupture of the finest lines.
PROCESS FOR HIGH ETCHING IN RELIEF.
Experienced etchers can also apply their art to the reproduction of drawings by means of the printer’s press, in the following manner:
A plate, ready for etching and free from grease, is cleaned with weakly acidified water, the remaining water drawn off with a blotter, and the plate gently heated. By means of a pad a fine paste of graphite is rubbed upon the surface; it is then moderately heated and a very thin gauze-like layer of warm white wax is applied to the graphite surface. After cooling the plate, spread upon it a coat consisting of the finest orange-colored chrome yellow (rubbed to a fine dough with water and gum). In this ground layer we can erase as for deep etching.
Brush the finished surface with writing ink dissolved in benzine (using a fine wide brush). The plate should be warm. Take a pad made of cotton, dip it into water and work over the surface in small circles until the image has become well developed. From this point we can continue according to the usual method.
J. O. MÖRCH.