Gilding is the art of applying gold-leaf or gold in a finely-divided state to surfaces of wood, stone, or metals. It is a very ancient art, being practised among the Egyptians, Greeks, Romans, and Ancient Persians. The processes employed through more modern times have been very varied. Metals are gilded either by what is called chemical gilding, mercurial gilding, by electro-gilding (electro-plating), or by the application of gold-leaf. Copper and brass, for instance, may be gilded by the process called wash or water gilding, with an amalgam of gold and mercury. The surface of the copper, freed from oxide, is covered with the amalgam, and afterwards exposed to heat until the mercury is driven off, leaving a thin coat of gold.
Gilding is also performed by dipping a linen rag in a saturated solution of gold, and burning it to tinder, the black powder thus obtained being rubbed on the metal to be gilded, with a cork dipped in salt water, until the gilding appears. Iron or steel is often gilded by applying gold-leaf, after the surface has been well cleaned, and heated until it has acquired the blue colour which at a certain temperature it assumes. Several leaves of gold are thus applied in succession, and the last is burnished down cold.
One process of chemical gilding was by dipping the article into a solution of gold, what is termed Elkington's solution being composed as follows: 5 oz. (troy) of fine gold; nitro-muriatic acid, 52 oz. (avoirdupois); dissolve by heat, and continue the heat until the cessation of red or yellow vapours; decant the clear liquid; add 4 gallons of distilled water, 20 lbs of pure bicarbonate of potassa and boiling for two hours.
Gilding on wood, plaster, leather, parchment, or paper, is performed by different processes of mechanical gilding. The first of these is oil-gilding, in which gold-leaf is cemented to the work by means of oil-size. In the case of paper or vellum the parts to be gilt receive a coat of gum-water or fine size, and the gold-leaf is applied before the parts are dry. They are afterwards burnished with agate. Lettering and other gilding on bound books are applied without size. The gold-leaf is laid on the leather and imprinted with hot brass types. Brass rollers with thin edges are employed in the same way for lines, and similar tools for other ornaments. When the edges of the leaves of books are to be gilt they are first cut smooth in the press, after which a solution of isinglass in spirits is laid on, and the gold-leaf is applied when the edges are in a proper state of dryness.
Japanner's gilding is another kind of mechanical gilding, which is performed in the same way as oil-gilding, except that instead of gold-leaf a gold dust or powder is employed. Frames of pictures and mirrors, mouldings, etc, are gilt by the application of gold-leaf, or by the cheaper process of 'German gilding,' that is, by tin-foil or silver-leaf, with a yellow varnish above.
Porcelain and other kinds of earthenware, as well as glass, may be gilt by fixing a layer of gold in a powdered state by the action of fire. The gold-dust or powder required in this operation may be obtained by precipitating it from a solution in aqua regia, either by means of iron sulphate or proto-nitrate of mercury. In order that the gold powder may be applied to the surface of the article to be gilt it must be well mixed with some viscous vehicle, such as strongly-gummed water. It is then laid on with a fine camel's-hair brush. Research Gilding
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General Information
Research Gilding
