Drinking glasses, and other utensils of this material, are sometimes, especially in Germany, gilt on their edges ; this is done in two ways, either by a simple ad hesive varnish, or by means of fire. The varnish is prepared, by dissolving in dry ing linseed oil a quantity of gum amine, or still better of clear amber, equal in weight to the linseed oil ; a very drying and adhesive varnish is thus prepared, which being diluted with a proper quan tity of oil of turpentine, is to be applied as thin as possible to those parts of the glass which are intended to be gilded ; when this is dry, which will be about a day, the glass is to be placed by the fire side, or in a stove, till it is so warm as almost to burn the fingers when handled; at this temperature the varnish will become glutinous, and a piece of gold leaf applied in the usual way will immediately adhere; when the gilding is thus put on, and be fore it is grown quite cold, it may be bur nished, taking care only to interpose a piece of very thin paper between the gold and burnisher. If the varnish is very good, this is the best method of gilding' glass, as the gold is thus fixed on more evenly than in any other way: it often happens, however, when the varnish is but indifferent, that by repeated wash ing the gold soon wears off: on this ac count, the practice of burning it in is sometimes had recourse to.
For this purpose some gold powder is tempered with borax, and in this state ap plied to the clean surface of the glass, with a clean camel's hair pencil: when quite dry, the glass is put in a stove heat ed to about the temperature of an anneal ing oven, the gum burns off, and the borax by vitrifying cements the gold with great firmness tp the glass; after which it may be burnisifed. The gilding upon porce lain is in like manlier fixed by fire and borax ; and this kind of ware being nei ther transparent nor liable to soften, and thus injure its form in a low red heat, is free from the risk and injury, which the finer and more fusible kinds of glass are apt to sustain from such treat ment.
All the methods of gilding hitherto described resemble each other, by being accomplished by means of some adhesive medium; this,however,is not the case with gilding upon metals ; the gold is brought into immediate contact with the other me tal, and they both remain firmly united merely by the attraction of adhesion sub sisting between them. The simplest of all the kinds of gilding on metal, and which strikingly demonstrates the power of the affinity of adhesion, is one which is sometimes practised on plane surfaces of copper and iron, with considerable suc cess. The metal, being previously polish ed, is heated to about the temperature of melted lead, and covered with a double layer of gold leaf: by the cautious appli cation ofa blood stone burnisher, applied gently at first, and increasing the force of the pressure by degrees, the surface of the gold and copper are brought to touch each other in almost e very point, and then adhere with a force proportionate to the completeness of the contact. The first
layer being thus burnished down, a se cond is made to adhere in the same man ner, and sometimes a third, if the gilding is intended to be very solid. The objec tion to this kind of gilding is its tedious ness, and the almost impossibility of using a sufficient pressure without injuring the evenness of the gilded surface : where these objections do not apply, there can not be a more effectual mode of gilding, as is evident from the manufacture of gilt silver and copper wire. The bar, before it is committed to the wire-drawer, is plated with gold, by having several plates of gold successively burnished down upon it,and being thensubjected to the stronger compression which takes place in wire drawing, the gold and the other metal in come so perfectly united as to form n a manner but one substance.
The most usual method of covering the face ofa metal with gold is by means of an amalgam, or, as it is technically called, water-gilding. If the metal to be gilt is silver, the best method of proceeding is, first to soak it in warm dilute muriatic acid,that the surface may be rendered per fectly clean ; it must then be washed in clean water, changed two or three times, to get rid of the whole of the acid : be ing afterwards dried, and made mode rately warm, a little gold amalgam, also warm, is to be carefully and evenly spread upon the silver, to which it will immedi ately adhere : when this is completed, the piece is placed upon a convenient support over a charcoal fire, and while the mercury is evaporating, if any specks or places appear, which have escaped the amalgam, a small piece is to be laid on and spread with a brush, to supply the deficiency, without removing the article from the fire. After a time, the whole of the mercury will be driven off, and the piece, after cooling, being accurate ly examined, will be found to be entire ly covered with a thin coating of pale dull gold. The small roughnesses, and loosely-adhering particles, are now to be removed with a scratch-brush, which is made of some extraordinary fine brass wire, bound together into a tuft ; by it the surface is rendered perfectly smooth and bright ; but it still remains of a pale yellowish colour : this defect is next removed by warming the piece, and smearing it over with gliders' wax, a composition of bees' wax, red ochre, verdigris, and green vitriol or alum. The wax being burnt over a charcoal fire, and the piece quenched in urine, the colour of the gilding will be found to be much heightened ; if it is not suffi ciently so, the application of a succeed ing one will complete. the desired ef fect, after which the work may be burn, ished or not, according to the taste of the artist. Instead of the common gilders' wax, a mixture of equal parts of nitre, sal-ammoniac, green vitro], and verdigris moistened with water, will an swer the purpose.