Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
GILDING
Online EncyclopediaEncyclopedia Home :: GEO-GNU
del.icio.us it!
|
GILDING , the See also:art of spreading See also:gold, either by See also:mechanical or by chemical means, over the See also:surface of a See also:body for the purpose of See also:ornament. The art of gilding was known to the ancients. According to See also:Herodotus, the Egyptians were accustomed to gild See also:wood and metals; and gilding by means of gold plates is frequently mentioned in the Old Testament. See also:Pliny informs us that the first gilding seen at See also:Rome was after the destruction of See also:Carthage, under the censorship of See also:Lucius See also:Mummius, when the See also:Romans began to gild the ceilings of their temples and palaces, the Capitol being the first See also:place on which this enrichment was bestowed. But he adds that luxury advanced on them so rapidly that in a little See also:time you might see all, even private and poor persons, gild the walls, vaults, and other parts of their dwellings. Owing to the See also:comparative thickness of the gold-See also:leaf used in See also:ancient gilding, the traces of it which yet remain are remarkably brilliant and solid. Gilding has in all times occupied an important place in the ornamental arts of See also:Oriental countries; and the native processes pursued in See also:India at the See also:present See also:day may be taken as typical of the arts as practised from the earliest periods. For the gilding of See also:copper, employed in the decoration of See also:temple domes and other large See also:works, the following is an outline of the processes employed. The See also:metal surface is thoroughly scraped, cleaned and polished, and next heated in a See also:fire sufficiently to remove any traces of grease or other impurity which may remain from the operation of polishing. It is then dipped in an See also:acid See also:solution prepared from dried unripe apricots, and rubbed with See also:pumice or See also:brick See also:powder. Next, the surface is rubbed over with See also:mercury which forms a superficial See also:amalgam with the copper, after which it is See also:left some See also:hours in clean See also:water, again washed with the acid solution, and dried. It is now ready for receiving the gold, which is laid on in leaf, and, on adhering, assumes a See also:grey See also:appearance from combining with the mercury, but on the application of See also:heat the latter metal volatilizes, leaving the gold a dull greyish See also:hue. The See also:colour is brought up by means' of rubbing with See also:agate burnishers. The See also:weight of mercury used in this See also:process is See also:double that of the gold laid on,and the thickness of the gilding is regulated by the circumstances or necessities of the See also:case. For the gilding of See also:iron or See also:steel, the surface is first scratched over with chequered lines, then washed in a hot solution of See also:green apricots, dried and heated just See also:short of red-heat. The gold-leaf is then laid on, and rubbed in with agate burnishers, when it adheres by catching into the prepared scratched surface. See also:Modern gilding is applied to numerous and diverse surfaces and by various distinct processes, so that the art is prosecuted in many ways, and is See also:part of widely different ornamental and useful arts. It forms an important and essential part of See also:frame-making (see See also:CARVING AND GILDING); it is largely employed in connexion with See also:cabinet-See also:work, decorative See also:painting and See also:house ornamentation; and it also bulks largely in See also:bookbinding and ornamental See also:leather work. Further, gilding is much employed for coating baser metals, as in See also:button-making, in the gilt See also:toy See also:trade, in electro-gilt reproductions and in electro-plating; and it is also a characteristic feature in the decoration of pottery, See also:porcelain and See also:glass. The various processes fall under one or other of two heads—mechanical gilding and gilding by chemical agency. Mechanical Gilding embraces all the operations by which gold-leaf is prepared (see See also:GOLDBEATING), and the several processes by which it is mechanically attached to the surfaces it is intended to See also:cover. It thus embraces the burnish or water-gilding and the oil-gilding of the See also:carver and See also:gilder, and the gilding operations of the house decorator, the sign-painter, the bookbinder, the See also:paper-stainer and several others. Polished iron, steel and other metals are gilt mechanically by applying gold-leaf to the metallic surface at a temperature just under red-heat, pressing the leaf on with a burnisher and reheating, when additional leaf may be laid on. The process is completed by See also:cold burnishing. Chemical Gilding embraces those processes in which the gold used is at some See also:stage in a See also:state of chemical See also:combination. Of these the following are the See also:principal: Cold Gilding.—In this process the gold is obtained in a state of extremely See also:fine See also:division, and applied by mechanical means. Cold gilding on See also:silver is performed by a solution of gold in aqua-regia, applied by dipping a See also:linen rag into the solution, burning it, and rubbing the See also:black and heavy ashes on the silver with the See also:finger or a piece of leather or See also:cork. Wet gilding is effected by means of a dilute solution of chloride of gold with twice its quantity of See also:ether. The liquids are agitated and allowed to See also:rest, when the ether separates and floats on the surface of the acid. The whole mixture is then poured into a See also:funnel with a small See also:aperture, and allowed to rest for some time, when the acid is run off and the ether separated. The ether will be found to have taken up all the gold from the acid, and may be used for gilding iron or steel, for which purpose the metal is polished with the finest See also:emery and See also:spirits of See also:wine. The ether is then applied with a small See also:brush, and as it evaporates it deposits the gold, which can now be heated and polished. For small delicate figures a See also:pen or a fine brush may be used for laying on the ether solution. Fire-gilding or See also:Wash-gilding is a process by which an amalgam of gold is applied to metallic surfaces, the mercury being subsequently volatilized, leaving a film of gold or an amalgam containing from 13 to 16% of mercury. In the preparation of the amalgam the gold must first be reduced to thin plates or grains, which are heated red hot, and thrown into mercury previously heated, till it begins to See also:smoke. Upon stirring the mercury with an iron See also:rod, the gold totally disappears. The proportion of mercury to gold is generally as six or eight to one. When the amalgam is cold it is squeezed through See also:chamois leather for the purpose of separating the superfluous mercury; the gold, with about twice its weight of mercury, remains behind, forming a yellowish silvery See also:mass of the consistence of See also:butter. When the metal to be gilt is wrought or chased, it ought to be covered with mercury before the amalgam is applied, that this may be more easily spread ; but when the surface of the metal is See also:plain, the amalgam may be applied to it See also:direct. When no such preparation is applied, the surface to be gilded is simply bitten and cleaned with nitric acid. A See also:deposit of mercury is obtained on a metallic surface by means of " quicksilver water," a solution of nitrate of mercury, the nitric acid attacking the metal to which it is applied, and thus leaving a film of See also:free metallic mercury. The amalgam being equally spread over the prepared surface of the metal, the mercury is then sublimed by a heat just sufficient for that purpose; for, if it is too See also:great, part of the gold may be driven off, or it may run together and leave some of the surface of the metal See also:bare. When the mercury has evaporated, which is known by the surface having entirely become of a dull yellow colour, the metal must undergo other operations, by which the fine gold colour is given to it. First, the gilded surface is rubbed with a scratch brush of See also:brass See also:wire, until its surface be smooth; then it is covered over with a See also:composition called " gilding See also:wax," and again exposed to the fire until the wax is burnt off. This wax is composed of beeswax mixed with some of the following substances, viz. red ochre, See also:verdigris, copper scales, See also:alum, See also:vitriol, See also:borax. By this operation the colour of the gilding is heightened; and the effect seems to be produced by a perfect dissipation of some mercury remaining after the former operation. The dissipation is well effected by this equable application of heat. The gilt surface is then covered over with See also:nitre, alum or other salts, ground together, and mixed up into a See also:paste with water or weak See also:ammonia. The piece of metal thus covered is exposed to a certain degree of heat, and then quenched in water. By this method its colour is further improved and brought nearer to that of gold, probably by removing any particles of copper that may have been on the gilt surface. This process, when skilfully carried out, produces gilding of great solidity and beauty; but owing to the exposure of the workmen to See also:mercurial fumes, it is very unhealthy, and further there is much loss of mercury. Numerous contrivances have been introduced to obviate these serious evils. Gilt brass buttons used for See also:uniforms are gilt by this process, and there is an See also:act of See also:parliament (1796) yet unrepealed which pre-See also:scribes 5 grains of gold as the smallest quantity that may be used for the gilding of 12 dozen of buttons 1 in. in See also:diameter.
Gilding of Pottery and Porcelain.—The quantity of gold consumed for these purposes is very large. The gold used is dissolved in aquaregia, and the acid is driven off by heat, or the gold may be precipitated by means of sulphate of iron. In this pulverulent state the gold is mixed with 112th of its weight of See also:oxide of See also:bismuth, together with a small quantity of borax and See also:gum water. The mixture is applied to the articles with a See also:camel's See also:hair See also:pencil, and after passing through the fire the gold is of a dingy colour, but the lustre is brought out by burnishing with agate and See also:bloodstone, and afterwards cleaning with See also:vinegar or See also: Additional information and CommentsThere are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML. Site content, images, and layout Copyright © 2006 - Net Industries, worldwide. |
|
|
[back] GILDERSLEEVE, BASIL LANNEAU (1831– ) |
[next] GILDS, or GUILDS |