Gilding is performed either with or without heat. By the first of these me thods those substances are gilt, which are not liable to alteration by exposure to a moderate heat, such as metals, and sometimes glass and porcelain : the se cond method is practised with those sub stances, such as wood, paper, lead, silk, lacquered and japanned ware, &c. which would be injured, and even destroyed, at the temperature requisite for gilding the former. The last of these methods, be ing the simplest, shall be firstdescribed, and we shall begin with the art of gilding on wood.
There are two methods for gilding on wood, namely, oil gilding and burnished gilding Oil gilding is thus performed the wood must first be covered, or prim ed, with two or three coatings of boiled linseed oil and white-lead, in order to fill up the pores, and to conceal the irre gularities of the surface occasioned by the veins in the wood. When the prim. ing is quite dry, a thin coat of gold-size must be laid on. This is prepared by grinding together some strongly calcined red ochre, with the thickest drying oil that can be procured, and the older the better : that it may work freely, it is to be mixed, previously to being used, with a little oil of turpentine, till it is brought to a proper consistence. Ifthe gold-size is good, it will be sufficiently dry in twelve hours, more or less, to allow the artist to proceed to the last part of the process, which is the application of the gold. For this purpose a leaf of gold is spread on the cushion (formed by a few folds of flannel secured on a piece of wood, about eight inches square, by a tight covering of leather), and is cut into strips of a proper size by a blunt pallet knife : each strip being then taken up on the point .of a fine brush is applied to the part intended to be gilded, and is then gently pressed down by a ball of soft cotton ; the gold immediately ad heres to the sticky surface of the sizo; and after a few minutes the dexterous ap plication of a large camel's hair brush sweeps away the loose particles of the gold leaf withoutdisturbing the rest. In a day or two the size will be completely dried, and the operation is finished. The advantages of this method of gilding are, that it is very simple, very durable, not readily injured by changes of weather, even when exposed to the open air, and when soiled it may be cleaned by a little warm water and a soft brush ; its disad vantage is, that it cannot be burnished, and therefore wants the high lustre pro duced by the next method. Its chief employment is in out-door work.
Burnished gilding, or gilding in distem per, is thus performed. The surface to be gilt must he carefully covered with strong size, made by boiling down two pieces of white leather, or clippings of parchment, till they are reduced to a stiffjelly ; this coating being dried, eight or ten more must be applied, consisting of the same size, mixed with fine Paris plaster or washed chalk : when a suffi cient number of layers have been put on, varying according to the nature of the work, and the whole is become quite dry, a moderately thick layer must be applied, composed of size and bole, or yellow ochre: while this last is yet moist, the gold leaf is to be put on inthe usual man ner; it will immediately adhere on being pressed by the cotton ball, and before the size is become perfectly dry, those parts which are intended to be the most bril liant are to be carefully burnished with agate or dog's tooth. In order to save
the labour of burnishing, it is a common, but bad practice, slightly to burnish the brilliant parts, and to deaden the rest by drawing a brush over them dipped in size: the required contrast between the polished and the unpolished gold is in deed thus obtained; but the general ef fect is much inferior to that produced in the regular way, and the smallest drop of water falling on the sized part occa sions a stain. This kind of gilding can only be applied on in-door work, as rain, and even a considerable degree of damp ness, will occasion the gold to peel off. When dirty, it may be cleaned with a soft brush, and hot spirit of wine, or oil of turpentine. It is chiefly used on pic ture frames, mouldings, and stucco.
Letters written on vellum or paper are gildedin three ways : in the first, a little size is mixed with the ink, and the letters. are written as usual; when they are dry, a slight degree of stickiness is produced by breathing on them, upon which the gold leaf is immediutely applied, and by a little pressure may be made to ad here with sufficient firmness. In a se cond method, some white-lead or chalk is ground up with strong size, and the letters are made with this by means of a brush: when the mixture is almost dry, the gold-leaf may be laid on, and af terwards burnished. The last method is, to mix up sonic gold powder with size, and make the letters of this by means of a brush. The edges of the leaves of books are gilded, while in the binder's press, by first applying a composition formed of four parts of Armenian bole and one of sugar candy, ground together to a proper consistence, and laying it on with a brush with the white of egg: this coating, when nearly dry, is smoothed by the burnisher; it is then slightly moistened with clean water, and the gold leaf applied, and afterwards burnished. In order to impress the gilt figures on the leather covers of books, the leather is first dusted over with very fine rezin, or mastich, then the iron tool by which the figure is made is moderately heated, and pressed down on a piece of leaf gold, which slightly adheres to it ; being then immediately applied to the surface of the leather with a certain force, the tool at the same time makes an impres sion, and melts the mastich which lies be tween the heated iron and the leather; in consequence oft this the gold with which the face of the tool is covered is made to adhere to the leather, so that on removing the tool a gilded impression of it remains behind.