GILDING, the art of applying and per manently attaching gold leaf or gold dust to surfaces of wood, stone, metals, etc. The Egyptian monuments present numerous traces of the existence of the art in ancient Egypt. The process to have been the same with that now used. The Persians also were ac quainted with this art as appears from the ruins of Persepolis. The Greeks and Romans em ployed gilding for many purposes. The Greeks used to gild the hoofs and horns of victims. The practice of gilding statues prevailed in the infancy of the art of sculpture and was never entirely dropped by the ancients. The Romans used to gild sweetmeats and many articles of furniture and utensils which have come down to us are gilt. There are also specimens of gilt glass and metals. The gilding which still re mains on some ancient bronze monuments is remarkable for its brilliancy. The ancients car ried the practice of gilding to a greater extent than the moderns; they gilded almost all their statues of bronze, wood or plaster and fre quently those of marble, the ceilings of rooms and even marble columns. The most remark able examples of gilding employed with taste and effect in architecture are the ceiling of Saint Peter's and that of Santa Maria Mag giore.
The art of gilding at the present day is per formed on metals, or on wood, plaster, leather, parchment, paper, glass, etc. Chemical proc esses are those which are usually employed for metals. Gilding on copper is performed by the process called wash or water gilding, with an amalgam of gold and mercury. The surface of the copper, being freed from oxide, is covered with the amalgam and afterward exposed to heat till the mercury is driven off, leaving a thin coat of gold. Copper, however, is rather too soft and dark-colored a metal to be treated in this way with advantage. Brass is a very suitable metal for this mode of gilding, but the best of all is a mixture of copper with one seventh of brass. Copper, brass, etc., are gilded by being attached to wires and plunged into a mixture, where they are allowed to remain as long as the workman thinks necessary, from a few seconds to a minute when the mixture is newly prepared, but longer if it has been used for some time. Gilding is also performed by dipping a linen in a saturated solution of gold, and burning it to tinder. The black
powder thus obtained is rubbed on the metal to be gilded with a cork dipped in salt water till the gilding appears. Iron or steel is gilded by applying gold leaf to the metal, after the surface has been well cleaned and heated till it has acquired the blue color which at a cer tain temperature it assumes. Several leaves of gold are thus applied in succession, and the last is burnished down cold. The same, process may be applied to copper. The operation of gilding may also be performed on iron and steel by diluting the solution of gold in nitro hydrochloric acid with alcohol and applying it to a clean surface. A saturated solution of gold in nitro-hydrochloric acid, being mixed with three times its weight of sulphuric ether, dissolves the chloride of gold and the solution is separated from the acid beneath. To gild the steel it is merely necessary, the surface being previously well polished and cleaned, to dip it in the ethereal solution for an instant, and on withdrawing it to wash it instantly by agitation in water. Before being gilded, masonry must be rendered waterproof by means of a solution of shellac and gutta percha in naphtha or some other coating.
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 gilded receive a coat of gum water or fine size to render them non absorbent, and the gold leaf is applied before the parts are dry. They are afterward bur nished 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 gilded 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.