(a) Dissolve any quantity of gold or platinum in nitro-muriaticacid, until no effervescence is occasioned by the application of heat. Evaporate the solution thus formed to dryness in a gentle heat, and redissolve the dry mass in as little water as possible; next take an instrument which is used by chemists for dropping liquids, known by the name of a separating funnel, having a pear-shaped body, tapering to a fine point, and a neck capable of being stopped with the finger or a cork; fill it with the liquid about one quarter part; and the other three parts must be filled with the very best sulphuric ether. If this is rightly managed, the two liquids will not mix. Then place the tube in a horizontal position, and gently turn it round with the finger and thumb. The ether will very soon be impregnated with the platinum or gold, which may be known by its change of colour. Replace it in a perpendicular position, and let it rest for 24 hours, having first stopped the upper orifice with a small cork. The liquid will then be divided into two parts; the darker coloured being underneath. To separate them, take out the cork, and let the dark liquid flow out; when it has disappeared, stop the tube immediately with the cork; and what remains in the tube is the gilding liquid.
Let it be put into a bottle, and tightly corked. When an article is to be gilded, a vessel of glass or unglazed ware must be provided, of just sufficient size to admit the article; it must then be filled with the gilding liquid, nearly to the top. The steel must be very highly polished, and entirely free from rust or grease. A basin, full of clean water, must be ready at hand, the article is immersed in the gilding liquid, and quickly removed; then quickly plunged into the water, and well rinsed; next dried with blotting paper, and placed in a temperature of 150° F. till it be completely heated throughout; it may then be polished with rouge and a soft leather, or be burnished. Pure gold must be employed. The ethereal solution may also be concentrated by gentle evaporation. Care must be taken not to wipe the steel until the heat has been applied. This gilding is an effectual protection against rust, and is very ornamental.
. (6) Make a solution of 8 oz. nitre and common salt, with 5 oz. crude alum in a sufficient quantity of water; dissolve 1 oz. gold thinly plated and cut; and afterwards evaporate to dryness. Digest the residuum in rectified spirit of wine or ether, which will perfectly abstract the gold. The iron is to be brushed over with this solution, and becomes immediately gilt.
In gilding small articles for watchmakers, gold is seldom directly applied upon the copper; there is generally a preliminary operation, called graining, by which a grained and slightly dead appearance is given to the articles.