15. GILDING GLASS AND PORCELAIN
Dissolve in boiling linseed oil an equal weight either of copal or amber, and add as much oil of turpentine as will enable you to apply the compound or size thus formed as thin as possible to the parts of the glass intended to be gilt; the glass is to be placed in a stove till it is so warm as almost to burn the fingers when handled. At this temperature the size becomes adhesive, and a piece of leaf gold applied in the usual way will immediately stick. Sweep off the superfluous portions of the leaf, and when quite cold it may be burnished, taking care to interpose a piece of india paper between the gold and the burnisher. It sometimes happens when the varnish is not very good that by repeated washing the gold wears off; on this account the practice of burning it in is sometimes had recourse to; for this purpose some gold powder is ground with borax, and in this state applied to the clean surface of the glass by a camel hair pencil; when quite dry the glass is put into a stove, heated to about the temperature of an annealing oven, the gum burns off; and the borax, by vitrifying, cements the gold with great firmness to the glass, after which it may be burnished.
The gilding upon porcelain is in like manner fixed by heat and the use of borax, and this kind of ware, being neither transparent nor liable to soften, and thus to be injured in its form in a low red heat, is free from the risk and injury which the finer and more fusible kinds of glass are apt to sustain from such treatment. Porcelain and other wares may be platinized, silvered, tinned, or bronzed, in a similar manner.