The New International Encyclopædia/Gilding
GILDING (from gild, AS. gyldan, from gold). The art of covering a surface with a thin layer of gold. There are many processes of gilding, varying with the nature of the substance to be gilded and the kind of effect desired. The different methods, however, may be grouped under the three general classes of mechanical gilding, chemical gilding, and encaustic gilding.
Mechanical Gilding consists of applying gold leaf directly to a surface which has been previously prepared by the application of a size. The gold leaf, being placed on the size while it is only partially dry, adheres. Various forms of gold leaf, and various substitutes as well, are used for gilding. There is the genuine deep or reddish gold; pale gold, the paleness being due to a silver alloy; silver leaf, afterwards colored or varnished to imitate gold; and ‘Dutch’ leaf, a copper alloy having an appearance similar to gold. The gilding material is sold in ‘books,’ a gold book usually containing 24 leaves, 3 inches square. Several different sizes are also used, of which the commonest are ‘old gold size,’ a mixture of litharge, linseed-oil, and ochre, and ‘water size,’ made by dissolving isinglass in boiling water, and adding an equal volume of spirits, and then straining the mixture through silk. Gilding may be applied in this manner to wood, cardboard or paper, textiles, metals, masonry, or ivory. When applied to cards, papers, or textiles, the surface must be rendered non-absorbent by a preliminary sizing of weak glue before the regular gilding size is applied. Before gilding a metal surface it must be painted, to protect the surface from oxidation and decay. Metals, however, are rarely gilded by the mechanical process. Masonry, before being gilded, must be ‘satisfied’ — that is, its porous surface must be rendered waterproof by a solution of shellac and gutta-percha, in naphtha or some other equally efficacious coating. In gilding ivory a warm size is applied. Plaster of Paris needs several preliminary coats of boiled linseed-oil before the gold size is applied. The object of the preparatory treatment of all surfaces is, of course, to secure a smooth, impenetrable, and permanent surface on which to lay the gold leaf. The leaf is accurately cut the desired shape, and applied to the sized surface by means of special tools. After being carefully brushed, to remove stray fragments, the gilding is given a final coat of specially prepared varnish. Glass is gilded by a special process. The gold sheet is made to adhere to the back of the glass simply by moistening it with the breath, the glass having been previously cleaned by a preparation of whiting, rubbed off with silk. The pattern is marked in reverse on the back, and that part of the gold inclosed in the pattern fixed by a coat of Brunswick black or other size. After this has thoroughly dried, the portions not included in the pattern are carefully rubbed off with wet cotton. 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 wholly covered with gold leaf, adhering with isinglass. The ornament is then painted on with asphaltum, 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.