. GILDING. There are many processes of gilding, varying with the nature of the substance to be gilded, and the kind of effect required to be produced, but they may all be classified under three heads—namely, 1st, mechanical gilding; 2d, chemical gild ing; 3d, encaustic gilding.
The first is used chiefly for gilding wood, plaster of Paris, leather, paper, and other substances. If the object to be gilded is a picture or mirror frame, consisting of a plain wooden molding, then after getting a coat of oil-paint, from 4 to 10 coats of fine whiting mixed with fine glue are put on, each'in its turn being smoothed with pumice stone and fine sand-paper. This done, a coat of gold-size is given to those parts which are not to be burnished; but those which are, receive only a coating of clear animal size. Both of these prepared surfaces now receive the gold-leaf, which is laid on by means of a broad thin brush called a tip, and further pressed on with a thick soft-haired brush. Those parts which have been gold-sized are in this way oil-gilt, and will stand washing; while such portions as have been gilded on the size preparation in order to be burnished, will not bear soap and water. If the picture frame is much enriched with raised ornament, then the various coatings of whiting are not smoothed with pumice or sand-paper. In many cases, and especially with outside work, the surface to be gilded is previously prepared with oil-paint and gold-size alone. The gold-size used for oil gilding is of different kinds. Sometimes it consists of coiled linseed-oil and ground ocher alone. Another kind has copal varnish and turpentine in addition. Japanners' gold-size is a mixture of lb. of linseed-oil, 2 oz. of gum-animi in powder, and some vermilion.
.Tapanners' gilding.—Where gilt ornaments are to be put on a japanned ground, they are, by one method, painted with gold-size, and gold-leaf afterwards applied. By another way, rather more than the space the ornament is to occupy is covered with gold-leaf, adhering with isinglass. The ornament is then painted on with asphal tum, which protects the gold beneath it while the superfluous leaf is being washed away. A little turpentine will then remove the protecting asphaltum so as to display the gilt ornament.
Falsegilding, although an cid invention, has become in recent years an important trade in Germany. It is usually applied to moldings for pictures, mirrors, and room
decoration. The molding intended to be gilded in this way is first covered with silver leaf or tin foil on a surface prepared as above, and then coated with a yellow varnish. A cheap and very durable imitation of genuine gilding is thus obtained, with which most of the less costly picture-frame moldings are now covered.
Chemical gilding.—Metals are now usually gilded by the process of electro-gilding (see GALvaxism), but besides this, various methods of chemical gilding have been adopted, and some are still in use.
Water or wash gilding, as it is somewhat inappropriately termed, consists in apply ing to metal a paste formed of an amalgam of gold, and afterwards evaporating the volatile mercury by heat, which leaves the gold firmly adhering to the surface of the metal. In preparing the amalgam, about eight parts of mercury to one of gold are used, but when this is squeezed through chamois leather, some mercury is removed, so that the amalgam actually applied contains about 33 per cent of gold. The metal to be gilded is cleaned with acid, brushed, and rubbed with bran or sawdust to make its surface perfectly clean. By means of a wire brush a solution of nitrate of mercury is then applied to it along with a portion of the gold amalgam. The mercury is driven off by heating at a charcoal fire, and the gilt surface is then ready for burnishing, which is done by rubbing it with a hematite burnisher. The deadening is produced by coat ing the surface with a mixture of sea salt, niter, and alum, and applying heat. Although modern appliances have diminished the evil, water gilding is still injurious to those who work at it, from the effect of the mercury fumes. It is worth noticing that this old process of gilding, although the contrary is often believed, is really better and more durable than electro-gilding. It is asserted that to the introduction of the latter method is to be attributed the decline of the once prosperous gilt button trade; at all events, the more costly kinds of decorative work in metal are now gilded as of old by the mer cury process. Thirty thousand buttons, one inch in diameter, may be gilded with one ounce of gold; 14 or 15 thousand is the number over which this quantity is commonly spread.