(6) By acids; giving a dead lustre to the metallic surface, before gilding, and by the processes indicated in the cleansing operations. This is employed for small articles, or when gilding by dipping, for bronze articles, or large embossed work.
(c) With frosted silver, by depositing upon the object to be gilt a coat of frosted silver, and then gilding in a good bath; this method is expensive, the burnished parts are greenish, and the intermediary coat of silver is more easily blackened by sulphur fumes than gold.
(d) By decomposing a solution of copper sulphate by a battery, depositing a coat of this metal, which possesses a pink dead lustre. The whole is rapidly passed through the. compound acids for a bright lustre, and the mercurial solution, and then gilt in a good bath. When the. dead lustre obtained in the bath is perfect, the compound acids may be dispensed with, and merely place the article in the mercurial solution before it is gilt. This mode is generally preferred, as the gilding is very handsome in lustre and colour. The burnished parts will be red, if vinegar or soap-water is used; and of a fine yellow colour, if the burnishing tool be wetted with a decoction of flax-seed, or of marsh-mallow root. If the gold deposit is of insufficient thickness, it will blacken in time, by the oxidation of the intermediate coat of copper. .
(e) Mercury furnishes the most durable gilding, although costly.
(f) For Zinc - With tin solder fill all the holes and the smallest defects which may exist in the zinc object, and, at the same time, remove all seams, burrs, and rough spots. Afterwards, scour the piece by passing it, for a few seconds only, through a boiling solution of 100 parts water and 5-6 caustic soda; if left too long in this caustic lye it will spoil the polish of the zinc, which dissolves. After this scouring, the object is rinsed in fresh water. It is then steeped for 1/2 minute in a pickle composed of 1 part sulphuric acid, and 10 water, and lastly rinsed in boiling water. Then place the object in a cold or warm electro-bath of copper or brass, for a few moments, until it is covered with a thin metallic coating, which is deposited very uniformly if the object has in it no tin solder, and is perfectly cleansed; the deposit is black and dull on those parts which have been soldered, or imperfectly cleansed. In this case, thoroughly scratch-brush the article, and dip again into the electro-bath until the deposit is sufficiently thick. Most gilders use a warm bath for the first coating, scratch-brush, and complete the deposit in a cold bath.
If a bright gilding is desired, the article may be rinsed in fresh water, and then dipped into an electro-gilding bath.