Adhering galvanoplastic deposits give a very cheap and handsome gilding with a dead lustre, which, although not equal in durability, has the appearance of that obtained with mercury. Having cleansed the mould if metallic, or rendered it a conductor if non-metallic, immerse it in the solution of copper sulphate, and allow the deposit to acquire a dead lustre slightly in excess of that desired. After this operation, which may last 2 to 6 hours, remove the article from the bath, rinse it in plenty of water, and pass it rapidly through the compound acids for a bright lustre, which diminish the previous dulness of the appearance. Next rinse in fresh water; steep in a mercurial solution similar to that employed for gilding by dipping; rinse again; and immerse in an electro-gilding bath made of, - Distilled water, 2 1/5 gal.; soda phosphate, 21 oz.; soda bisulphite, 3 1/2 oz.; potassium cyanide, 2/3 oz; gold, for neutral chloride, 1/3 oz. At first, the current is rendered sufficiently intense by dipping the platinum anode in deeply; afterwards the intensity is diminished by partly withdrawing the anode until the entire shade of gold is obtained. This gilding requires but little gold, as the frosty dead lustre comes from the copper.
When the lustre of the copper is very fine and velvety, dispense with the dipping into the compound acids, but the rapid passage through the mercurial solution is always desirable. If the deposited gold is not uniform, or appears cloudy, it is proof of an imperfect deposit in the bath, or of an insufficient steeping in the compound acids. The piece should then be removed from the bath, washed in a tepid solution of potassium cyanide, rinsed in fresh water, dipped in the solution of nitrate of binoxide of mercury, and electro-gilded anew. This gilding bears burnishing well; avoid acid waters and soap, which will produce a red polish, and use only the fresh solutions of linseed, or of marsh-mallow root. The tone of gold thus obtained is richer, deeper, and more durable than that produced upon frosted silver, the latter being recognised by the green colour of the burnished parts. This kind of deposit may be employed for binding substances together, because the covering coat will be continuous.
After thoroughly cleaning the pattern, rub it with a brush charged with plumbago, or with a soft brush slightly greased by a tallow candle. The film of fatty substance should not be seen at all. The deposit obtained represents an inverted image of the pattern, and the raised parts become hollow. Remove the mould, and perform the same operation upon the deposit; this second deposit is the accurate reproduction of the first pattern.
By this process porcelain, crystal, plaster of Paris, wood, flowers, fruits, animals, and the most delicate insects may be coated. These substances have no conductive power for electricity; it is, therefore, necessary to metallise them.