§ 135 Preparing Surfaces for Gilding.
Ordinary brass work — rough or smooth — may for purposes of preservation be dipped, scratch-brushed, and gilt at once. Seven years ago the writer gilt the inside of the head of a copper water still, and simply scratch-brushed it; it is to-day in as good order as when it was first done. If it is intended to gild work from the first, with the view of making an exceptionally fine job of it, “gilding metal,” i.e. brass containing one to one and a quarter ounces of zinc to the pound of copper may be specified. From its costliness, however, this is only desirable for small work.
Iron and steel are generally given a preliminary coating of copper, but this may be dispensed with though with no advantage — by using a particular process of gilding.
Base metals, zinc, pewter, lead, etc., are first coppered in a cyanide of copper solution, as will be described under the head of Copper-plating. If it is intended to gild soldered articles, the preliminary coating of copper is essential.
The most convenient vessel for holding a gilding solution is undoubtedly one formed of enamelled iron. Particularly useful are the buckets and “billies” (i.e. cylindrical cans) made of this material. These vessels may be heated without any fear of a smash, and do not appear to be appreciably affected by gilding solutions — at all events during several days or weeks. The avoidance of all risk of breakage when twenty or thirty pounds’ worth of solution is in question is a matter of importance.
Under no circumstances is it desirable to use anything but the purest gold and best fused cyanide (called “gold” cyanide) in the preparation of the solutions. The appearance of a pure gold deposit is far richer than of one containing silver, and its resistance to the atmosphere is perfect; moreover, in chemico-physical processes one has the satisfaction of knowing what one is dealing with.