Manufacturer and builder 1, 1884
The Gewerbeblatt gives the following:
Thirty grams of acetate of copper are ground into a fine powder in a mortar, then spread out in a thin layer on a porcelain plate and left for a few days in a moderately warm place. By this time the water of crystallization and most of the acetic acid will have escaped. The light brown powder that is left is triturated with some oil of turpentine in a mortar, and then stirred into 100 grams of fine fatty copal varnish warmed to 75° C. If the acetate of copper is exceedingly fine, the greater part of it will dissolve by a quarter hour's stirring. The varnish is then put in a glass bottle and placed for a few days in a warm place, shaking frequently. The small quantity of acetate of copper that settles can be used in making the next lot. This varnish is dark green, but when applied to tin it requires four or five coats to get a fine luster; but two coats are sufficient, if heated in a drying closet or on a uniformly heated plate, to produce a great variety of shades of gold. A greenish gold, a yellow or dark yellow gold, then an orange, and finally a reddish brown shade is obtained, according to the time and temperature. The colors are superior in brilliancy to those obtained with the English gold varnishes, and have the advantage of permanency in the light. If a good copal varnish is used in making this polychromatic varnish, or lac, the tin can be hammered or pressed. The production of golden colors depends on the reduction of cupric oxide to cuprous oxide (protoxide to suboxide), which, in small quantity, dissolves in the copal varnish with a golden color. The more the heat the greater the reduction, and hence the darker the color. Success depends upon applying it evenly and warming uniformly.