G I L

GIL

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the moil; extenfible of all fubftances : fo that agiven weight of gold, notwithftanding its highfpecific gravity, may by beating be made tocover a larger furface than an equal quantity ofany other body. Among the ancients, the Ro-mans, and among the modems, the French havebeen remarkable for their large and profufeconfumption of gold : not only the temples,theatres, and other public buildings being adorn-ed with gilding, but even the private houfes ofthe wealthier c!affes.

The materials of gilding, or rather the dif-ferent ftates in which gold is ufcd for this pur-pofe, are the following : leaf-gold, of differentthickneffes and formed either of the pure metal,or of an alloy of this with fiver, amalgam ofgold, and gold powder. The leaf-gold is pro-cured by the gilder from the gold-beater, foran account of which we (hall refer the readerto the article Gold ; but the other two fub-ftances being prepared by the gilder himfelfmay be with propriety defcribed here. Theamalgam of gold is made by heating in a cleancrucible fome pure quickfilver, and when it isnearly boiling adding to it about a fixth of itsweight of fine gold in thin plates heated redhot; the mixture after being kept hot for a fewminutes becomes of a perfectly homogeneousconfidence, and may then be allowed to cool:when cold it is to be put in a piece of foftleather, and by gradual prelfure the fluid partof the timalgam conffiing almoft wholly ofmercury may be forced through the pores ofthe leather, while the gold combined with abouttwice its weight of mercury will remain behindforming a yellowifh filvery mafs of the eon-filtence of foft butter. This after being bruifedin a mortar, or fhaken in a ftrong vial with re-peated portions of fait and water till the watereeafes to be fouled by it, is fit for ufe, andmay be kept for any length of time without in-jury in a corked vial. It is of effential import-ance that the materials of this- amalgam, andcfpecially the mercury, Ihould be perfectly pure,as the leaf!; portion of lead or bifmuth wouldvery materially injure the beauty of the gildingby deteriorating the colour of the gold and fill-ing it with black fpecks ; on this account nomercury ought to be employed that has notbeen procured from diftillation of the red pre-cipitate (nitrous red oxyd of mercury) eitheralone or mixed with a little charcoal powder.

Gold powder is prepared in three differentways. The firft and fimpleft is. to put into aglafs or earthen mortar fome gold-leaf with alittle honey or thick gum-water, and grind the

mixture for a confiderable time, till the gold Isreduced to extremely minute fragments ; whenthis is done a little warm water will wafh out.the honey or gum, leaving the gold behindin a flaky pulverulent ftate. A lefs tediousand more effectual way of comminuting thegold is to diflolve it in nitro-muriatic acid andthen precipitate it by a piece of copper : theprecipitate after being digefted -in diftilled vine-gar and then well wafhed' in water and dried,is in the form of a very fine powder, and bothworks better and is eafier to burnifh than theground leaf-gold. The fined ground gold how-ever is produced by heating very gradually thegold-amalgam in an open earthen vefiel, andcontinuing the fire till the whole of the mer-cury is evaporated, taking care that the amal-gam fhall be conftantly ftirred with a glafs rodor tobacco-pipe, in order to prevent the par-ticles of gold from adhering as the mercuryflies off. When the mercury is compleatlyevaporated the refidual gold being then groundin a Wedgewood ware mortar with a littlewater, and afterwards dried, is fit for ufe.

Gilding is performed either with or withoutthe application of heat. By the firft of thefemethods thofe fubftances are gilt which are notliable to alteration by expofure to a moderateheat, fuch as metals and fometimes glafs andporcelain: the fecond method is pradtifed withthofe fubftances, fuch as wood, paper, leather,filk, lacquered and japanned ware, &c. whichwould be injured, and even deftroyed at thetemperature requifite for gilding the former.The lafi; of thefe methods being the fimpleft fhallbe firft defcribed; and we fhall begin with theart of gilding on wood. •

There are two methods of gilding on wood,namely, oil-gilding and burnifhed gilding. Oil—ilding is thus performed. The wood mullrft be covered or primed with two or threecoatings of boiled linfeed-oil and white-lead, inorder to fill up the pores and conceal the ir-regularities of the furface occafioned by theveins in the wood. When the priming, is quitedry a thin coat of gold-fize muft be laid on.This- is prepared by grinding together fome.ftrongly calcined red ochre with the thickeftdrying oil that can be procured, and the olderthe better : that it may work freely it is to bemixed, previoufly to being ufed, with a littleoil of turpentine till it is brought to a properconfiftence. If the gold-fize is good it will befufficiently dry in twelve hours, more or lefs, toallow the artift to proceed to the la ft part ofthe procefs, which is the application of the