Another, and perhaps better method of preparing gold powder is to heat a prepared amalgam of gold in a clean open crucible, (an amalgam of any metal is formed by a mixture of quicksilver with that metal) continuing a very strong heat till all the mercury has evaporated, stirring the amalgam all the while with a glass rod; when the mercury has entirely left the gold, grind the remainder in a Wedgewood's mortar, with a little water, and when dried it will be fit for use. The subliming the mercury is, however, a process injurious to the health. 171. COLOUR HEIGHTENING COMPOSITIONS For yellow gold, dissolve in water 6 ozs. of saltpetre, 2 ozs. of copperas, 1 oz. of white vitriol, and 1 oz. of alum. If wanted redder, add a small portion of blue vitriol. 172. FOR GREEN GOLD Dissolve in water a mixture consisting of 1-1/2 oz. of saltpetre; vitriol and sal-ammoniac, 1-1/4 oz. of each, and 1 oz. verdigris. 173. FOR RED GOLD Take 1-1/2 oz. of red ochre in fine powder, the same quantity of calcined verdigris, 1/2 oz. of calcined borax, and 4 oz. of melted yellow wax; the verdigris must be calcined, or else, by the heat applied in melting the wax, the vinegar becomes so concentrated as to corrode the surface, and make it appear speckled. These last three are colours for heightening compositions. 174. MOSAIC GOLD Mosaic gold, or aurum mosaicum, is used for inferior articles. It is prepared in the following manner: 1 lb. of tin is melted in a crucible, and 1/2 lb. of purified quicksilver added to it; when this mixture is cold, it is reduced to powder, and ground with 1/2 lb. of sal-ammoniac, and 7 ozs. of flower of sulphur, till the whole is thoroughly mixed; they are then calcined in a mattrass, and the sublimation of the other ingredients leaves the tin converted into the aurum mosaicum, which is found at the bottom of the glass, like a mass of bright flakey gold powder. Should any black or discoloured particles appear, they must be removed. The sal-ammoniac used here must be very white and clear, and the mercury quite pure and unadulterated. When a shade of deeper red is required, it can easily be obtained by grinding a very small quantity of red lead along with the above materials. 175. DUTCH OR GERMAN GOLD A gilding powder is sometimes made from Dutch gold, which is sold in books at a very low price. This is treated in the same way as the real gold leaf in making the true gold powder. It is necessary, when this inferior powder is used, to cover the gilding with a coat of clear varnish, otherwise it soon loses its metallic appearance. The same remark applies, though to a less degree, to Mosaic gilding. 176. COPPER POWDER