the art of spreading or covering gold, either in leaf or in liquid, over the surface of a body for the purpose of ornament. The art of gilding was not unknown among the ancients. According to Herodotus, the Egyptians were accustomed to gild wood and metals; and gilding by means of gold plates is frequently mentioned in the books of the Old Testament. Pliny informs us that the first gilding seen at Rome was after the destruction of Carthage, under the censorship of Lucius Mummius, when the Romans began to gild the ceilings of their temples and palaces; the Capitol being the first place on which this enrichment was bestowed. But he adds, that luxury advanced on them so rapidly, that in a little time you might see all, even private and poor persons, gild the walls, vaults, and other parts of their dwellings.

We need not doubt that they had the same method as ourselves of beating gold, and reducing it into leaves; though it should seem that they did not carry it to the same extent, if it be true, as Pliny relates, that they only made 750 leaves of four fingers square out of an ounce. Indeed he adds that they could make more; that the thickest were called bracteae Prænestinae, by reason of a statue of the goddess Fortune at Praeneste gilt with such leaves; and that the thinner sort were called bracteae questoriae.

The modern gilders also make use of gold leaves of different thickness; but there are some so thin as not to exceed \( \frac{1}{200} \) of an inch in thickness. The thicker sorts are used for gilding on iron and other metals, and the thinnest on wood. But we have many advantages over the ancients in the manner of using or applying the gold. The secret of water gilding, discovered of late ages, furnishes us with means of gilding works capable of enduring all the injuries of time and weather, which to the ancients was impracticable. They had no method of laying on the gold on bodies so as to endure the fire; their method was to attach it by means of the albumen of eggs or size; but as this will not resist the action of moisture, they could only gild in such places as were sheltered.

The Greeks called the composition on which they applied their gilding on wood leucophoenum or leucophorum; which is described as a sort of glutinous compound earth, serving in all probability to make the gold stick and bear polishing. But antiquaries and naturalists are not agreed as to the particulars of this earth, its colour, and ingredients.

The lustre and beauty of gold have led to several inquiries and discoveries concerning the different methods of applying it to different substances. Hence the art of gilding is varied, and involves several distinct processes.

Gilding is chiefly of two kinds, entirely distinct from each other, according as the material to be gilded is wood or metal. Gilding on wood is also of two kinds, known as burnish-gilding and oil-gilding. In burnish-gilding the following are the processes for a plain picture-frame. The gilder procures from the joiner a bevelled moulding twelve

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1 See Beckmann, History of Inventions, the Chapter on Gilding. Gilding, feet in length. He prepares this for gilding by a number of coats of priming; the first coat consisting of hot size and whiting, and called thin white. This is prepared by melting the size in an earthen pipkin, stirring in the size in a fine powder in small portions at a time. When the first coat is dry the surface is examined, and holes and irregularities are filled up with a putty formed of whiting and size. Four or five successive layers of thick white are then laid on. This is prepared in a manner similar to the thin white, only of greater consistence, and time is allowed for the work to dry between every two coats. To prevent the fine work of the moulding from being filled up, opening tools such as crooks, chisels, gouges, &c., are used while the thick white is wet, and in some cases two thick whites are laid on, one almost directly after the other, and are worked into the shape of the mouldings by means of hard stones of the required shape, which are used in conjunction with the opening tools. The whiting may now be from \( \frac{1}{4} \)th to \( \frac{1}{2} \)th of an inch in thickness, the edges are trimmed even, and the surface is smoothed with pumice-stone of the required form, the work being slightly wetted to promote the smoothing effect. The final polish is given with glass paper. Gold size is now put on in from four to eight coats, with dryings between. The size consists of pipe-clay, red chalk, black lead, suet, and bullock's blood; a portion of this is melted with thin clear size, and is laid on slightly warm with a brush.

The tools used by the gilder consist of the cushion, the knife, and the tip. The cushion is a flat board eight inches by six, covered with layers of woollen cloth or flannel, over which is strained a piece of leather. Along one of the short sides, and reaching half round each of the long sides, is a rim or border of parchment three inches high, which serves to prevent the gold-leaf from being blown about. The knife used for cutting gold-leaf has a straight smooth edge, ending in a well-defined point. The tip used for laying on the gold is a row of camel's hairs fastened between cards, and projecting from one inch to two inches and a half. The gold-leaf is supplied to the gilder in books, each containing 25 leaves. The gilder supports the cushion on his left hand by means of a leathern loop, and with the tip, the knife, and a camel's-hair pencil between the fingers of his left hand, he opens the book of leaf-gold with his right, and blows a number of leaves sufficient for his work upon the cushion; then taking one leaf he spreads it out upon the leather by a few dexterous manipulations with the knife, assisted by the breath. He next cuts it into strips suited to the width of the moulding; then wetting a few inches thereof with the camel's-hair pencil, he applies the tip to a slip of gold, which slightly adheres to the hairs, and enables him to transfer it to the moulding. Should the tip fail to take up the gold, the hairs are rubbed briskly across the face, or against the palm of the hand, and the friction, probably exciting the hairs electrically, enables them to take up the gold. The leaf being laid on, the gilder blows forcibly upon it, and uses a dry camel's-hair pencil to press down such parts as do not adhere. Another portion of the moulding is next wetted, and another piece of gold-leaf is laid on so as slightly to overlap the former. The whole moulding being in this way covered, it is set aside to dry.

The next process is burnishing, which is done with pieces of agate set in sticks; and these being rubbed over the surface greatly increase the brilliancy of the gold, an effect which is promoted by the yielding foundation of gold-size and whitening. The parts which are to be in dead or matt gold are left unburnished; a thin clear size is passed over them, and when dry, the gold is wiped with cotton wool, and defective places are restored with pieces of leaf-gold. When dry, the whole is finished by wetting the matt parts with a pencil dipped in clear finishing size. The moulding is now passed to the frame-maker, who cuts it up and forms the pieces into a frame. It is then returned to the gilder, who stops up nail-holes, and paints the sides of the frame yellow.

In oil-gilding the moulding is whitened as in the former case, and is at once made up into a frame. Composition ornaments are then put on, and the gilder now proceeds first by washing the frame to remove oil, &c. He next gives it two or three coatings of thin white, with additional coatings to the parts intended to be burnished. Two or three coats of a moderately strong size called clear-cole are laid on, after which the oil gold-size is applied, which consists of a mixture of boiled linseed oil and ochre. After some hours, the gilding is performed as before, except that no water is used, the partially dried oil serving the purpose. For deep ornaments, the gold is pressed in with cotton wool, and has to be repeated to get rid of those irregular fractures called by the gilders "spiders' legs." The work has at first a ragged appearance, but it is now carefully gone over with the brush, smoothed, and any defective part restored. This is called skewing, and the superfluous gold removed during the process is known as skewings. The parts to be burnished are next worked, and the frame is lastly sized with clear size, and yellowed on the outside.

The method of applying gold to metals is entirely different from the above, and is done in various ways. One of these is by previously forming the gold into a paste or amalgam with mercury, for which purpose 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 smoke. Upon stirring the mercury with an iron 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 chamois leather for the purpose of separating the superfluous mercury; the gold, with about twice its weight of mercury, remains behind; it is a yellowish silvery mass of the consistence of butter, and with this amalgam the surface of the metal to be gilded is to be covered; then a sufficient heat is to be applied to evaporate the mercury; and, lastly, the gold is to be burnished with a bloodstone.

This method of gilding by amalgamation is chiefly used for gilding copper, or an alloy of copper with a small portion of zinc, which more readily receives the amalgam; and it is also preferable for its colour, which more resembles that of gold than the colour of copper. When the metal to be gilt is wrought or chased, it ought to be covered with quicksilver before the amalgam is applied, that this may be more easily spread; but when the surface of the metal is plain, the amalgam may be applied directly to it. It is to be observed that the use of the bloodstone is now generally abandoned, and a steel burnisher substituted for it. The steel burnisher is case-hardened and then polished; and the clearer the polish is, the brighter will the metal be burnished. The quicksilver or amalgam is made to adhere to the metal by means of a little aquafortis, which is rubbed on the metallic surface at the same time, and by which such surface is cleansed from any rust or tarnish that might prevent the union or adhesion of the metals. The nitrous acid also facilitates the application of the amalgam to the surface by dissolving part of the mercury of the amalgam; and when this solution is applied to the copper, the latter metal, having a stronger affinity for nitrous acid than the mercury has, precipitates the mercury upon its surface, in the same manner as a polished piece of iron precipitates copper upon its surface from a solution of blue vitriol. When the metal to be gilt is thus covered over with a thin precipitated coating of mercury, it readily receives the amalgam. The amalgam being equally spread over the surface of the metal to be gilt, by means of a brush, the mercury is then to be evaporated by a heat just sufficient for that purpose; for if it be too great, part of the gold may also be expelled, and part of it will run together, and leave some of the surface of the metal bare. Whilst the mercury is evaporating, the work should be from time to time taken from the fire, that it may be examined, that the amalgam may be spread more equally by means of a brush, that any defective parts of it may be again covered, and that the heat may not be too suddenly applied to it; and when the mercury has evaporated, which is known by the surface having entirely become of a dull yellow colour, the metal must then undergo other operations, by which the fine gold colour is given to it.

First, the gilded surface is rubbed with a scratch brush of brass wire, until its surface be smooth; then it is covered over with a composition called gilding wax, and again exposed to the fire until the wax be burnt off. This wax is composed of bees'-wax, mixed with some of the following substances, viz., red ochre, verdigris, copper scales, alum, vitriol, borax; but, according to Dr Lewis, the saline substances alone are sufficient, without any wax. 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 a saline composition, consisting of nitre, alum, or other vitriolic salt, ground together, and mixed up into a paste with water or urine. The pieces 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 which may happen to lie on the gilded surface. Lastly, some artists think that they give an additional lustre to their gilt work by dipping it in a liquor prepared by boiling some yellow materials, as sulphur, orpiment, or turmeric. The only advantage of this operation is, that a part of the yellow matter, as the sulphur or turmeric, remains in some of the hollows of the carved work, in which the gilding is apt to be more imperfect, and to which it gives a rich and solid appearance.

In the gilding of iron and steel it is difficult to prevent the oxidation of the metal during the volatilization of the mercury; and the temper of the metal in sword-blades, daggers, &c., is liable to be injured in the process. In ornamenting iron and steel, however, a solution of mercury in nitrous acid, called quicksilver-water, is used; the acid attacks the iron, and deposits in its place a thin coating of mercury, which unites with the gold amalgam after it is applied. By this method a bright durable gilding cannot be obtained.

By another method a solution of sulphate of copper is applied by a camel's-hair pencil, after which an amalgam of gold is laid on, and the mercury is driven off by heat. It is, however, more usual to burnish down the gold-leaf upon the steel with the assistance of heat.

By another process a solution of gold is made with nitro-muriatic acid; about twice the quantity of ether is then cautiously added in a large vessel; the liquids are agitated and allowed to rest, when the ether will separate and float on the surface of the acid. The whole mixture is then poured into a funnel with a small aperture, and allowed to rest for some time, when the acid is run off and the ether separated. The ether has 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 emery and spirits of wine. The ether is then applied with a small brush, and as it evaporates it deposits the gold, which can now be heated and polished. For small delicate figures a pen or a fine brush may be used for laying on the ether.

What is called cold gilding on silver is performed by a solution of gold in aqua-regia, applied by dipping a linen rag into the solution, burning it, and rubbing the black and heavy ashes on the silver with the finger or a piece of leather or cork.

Fine instruments of brass are sometimes gilt in order to preserve their surface, for which purpose a saturated solution of gold is evaporated until crystals begin to form; these are dissolved in water, into which the articles to be gilded are immersed. Washing and burnishing complete the process.

In the drying off or removing the mercury by volatilization the health of the workpeople is seriously injured by the fumes of the mercury; so much so, as formerly to make this the most unhealthy of employments, to say nothing of the loss of mercury. Various contrivances, by Dr Lewis and others, have done much to remedy the evil. In the modern gilding furnace buttons and similar small articles are put into a wire cage within a furnace, constructed so as to preserve and condense the fumes of mercury by carrying them with the draught through a kind of labyrinth containing water, the centre of the labyrinth communicating by an inclined pipe with the chimney, which discharges the smoke almost entirely free from metallic fumes.

The grand improvement which has been made of late years in the art of gilding metals has been the application of galvanism or voltaic electricity, founded on the fact that when a voltaic current is passed through a metallic solution decomposition takes place; the metal in a revived form attaches itself to the negative pole or electrode, while the acid or alkali goes to the positive pole. In the process of electro-gilding a gold solution is formed by dissolving gold in nitro-muriatic acid, which is digested with calcined magnesia, and the gold is precipitated as an oxide; this is boiled in strong nitric acid, washed, and dissolved in cyanide of potassium, which forms cyanide of gold and potassium. This solution is used at a temperature of at least 130° Fahr.

The positive electrode of the battery is of gold, the negative of iron or of copper. The articles to be gilded are cleansed by boiling in an alkaline ley and other solutions, and they are then hung on wires and suspended from the wire which crosses the mouth of the vat or gilding vessel from the negative pole. A small article may be gilt in three or four minutes. In gilding articles of iron, tin, or lead, a thin coating of copper is first deposited upon them, and upon this the gilding is deposited. The gilding solution usually contains from \( \frac{1}{2} \) to 1 oz. of gold in the gallon; but for small articles, such as rings, thimbles, &c., a weaker solution is used. The durability of the article depends, of course, on the quantity of gold deposited; but the appearance of gold (or colour, as it is called) may be given by a few grains to a very large surface. A very thin layer of gold upon silver will be of a light colour. For articles not exposed to wear, a mere blush of gold will give them a very ornamental appearance; but for watch-cases, pencil-cases, chains, &c., the coating should be thick. Mr Napier states that an ordinary-sized watch-case should have from 20 grains to 1 pennyweight of gold—a covering that will last 5 or 6 years. Small silver chains should have 12 grains, pencils from 3 to 5 grains, and a thimble from 1 to 2 grains.

The springs and works of chronometers are sometimes electro-gilt; and we have known a coat of gold to be deposited on plates intended for etching, instead of the usual varnish, and through this delicate layer the design has been traced and afterwards bitten in.

The beauty and durability of gold, and its unchanging nature, have led to its employment on various domestic articles, such as those of porcelain. For this purpose the gold is dissolved in aqua-regia, 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 \( \frac{1}{15} \)th of its weight of oxide of bismuth, together with a small quantity of borax and gum-water. The mixture is applied to the articles with a camel's-hair 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 bloodstone, and is lastly cleaned with vinegar or whitelead.

The art of gilding is of extensive application in orna- menting the covers of books. The parts intended to be gilt are covered with a thin layer of ovalbumen or white of egg called glaire, and then with a film of leaf-gold; on pressing upon this a heated brass tool containing the letter or device intended to be impressed, the gold becomes permanently fixed, and the superfluous portion is wiped off with a rag. The whole of the lettering and ornaments on the back and sides of a book-cover are commonly impressed at one operation, in what is called a blocking-press, for which purpose the pattern is cut out in a thick plate or block of brass attached to the upper bed of the press. In this upper bed is a cavity containing a row of gas jets for keeping the block at the proper temperature. The cloth book-cover, previously covered with gold-leaf at the parts intended to be ornamented, is placed within a metal gauge in the lower bed, when by means of a lever the upper bed is brought down, and the heated block is firmly pressed against the cover. In this way a large number of cloth covers are quickly ornamented. In leathern binding, however, the gold-lettering and ornaments are usually applied after the cover is on by the process of gold or hand-tooling.