The principal colours of gold for gilding are red, green, and yellow. These should be. kept in different amalgams. The part which is to remain of the first colour, is to be stopped off with a composition; of chalk and glue; the variety required is produced by gilding the unstopped parts with the proper amalgam, according to the usual mode of gilding. Sometimes the amalgam is applied to the surface to be gilt, without any quick-ing, by spreading it with aquafortis; but this depends on the same principle as a previous quicking. Cold Gilding with the Rag. - Dissolve finely laminated pure gold in aqua regia made of 5 parts nitric acid, 2 sal-ammoniac, 1/2 saltpetre. Heat carefully upon a gentle fire; when all the gold has disappeared, pour the cooled contents of the flask into a flat-bottomed stoneware pan. Into this liquor, place one upon the other, and in sufficient quantity, squares of linen cloth; strike them with a glass rod, in order that they may equally absorb the gold chloride. Each square of cloth is taken out with wooden pincers, well drained, and spread for drying in a dark chamber. When nearly dry, each piece of cloth, supported upon glass rods, is placed on top of a charcoal fire, and soon takes fire.
The combustion is aided by the presence of the saltpetre, and is finished upon a marble slab. Grind the ashes under a muller, collect and keep them between the folds of a parchment leaf, around which a wet cloth has been folded. The powder is then ready to use; mix it upon a slab with a few drops of water, and with this paste rub the well-cleaned surfaces of the silver to be gilt. The smooth surfaces are rubbed with the thumb, the fillets or grooves with a fine cork cut to the proper shape, and the corners or angles with a stick of soft wood, such as linden or poplar; the articles are then burnished. This gilding is very thin, but quite resisting, especially after the * action of the burnishing tool, which forces the gold into the pores of the silver. If a red shade be desired, add a small proportion of pure copper to the gold to be dissolved in aqua regia.