GILDING 



passes through the bag, under the pressure of the fingers, holds a good deal of gold in 

 solution ; and is employed in making fresh amalgam. 



Preparation of the mercurial solution. The amalgam of gold is applied to brass, 

 through the intervention of pure nitric acid, holding in solution a little mercury. 



100 parts of mercury, and 110 parts by weight of pure nitric acid, specific gravity 

 1-33, are to be put into a glass matrass. On the application of a gentle heat the mer- 

 cury dissolves with the disengagement of fumes of nitrous gas, which must bo allowed 

 to escape into the chimney. This solution is to be diluted with about 25 times its 

 weight of pure water, and bottled up for use. 



1. Annealing The workman anneals the piece of bronze after it has come out of 



the hands of the turner and engraver. He sets it among burning charcoal, or rather 

 peats, which have a more equal and lively flame ; covering it quite up, so that it may 

 be oxidised as little as possible, and taking care that the thin parts of the piece do not 

 become hotter than the thicker. This operation is done in a dark room, and when he 

 sees the piece of a cherry-red colour, he removes the fuel from about it, lifts it out 

 with long tongs, and sets it to cool slowly in the air. 



2. The decapage. The object of this process is to clear the surface from the coat of 

 oxide which may have formed upon it. The piece is plunged into a bucket filled with 

 extremely dilute sulphuric acid ; it is left there long enough to allow the coat of oxide 

 to be dissolved, or at least loosened ; and it is then rubbed with a hard brush. When 

 the piece becomes perfectly bright, it is washed and dried. Its surface may, however, 

 be still a little variegated ; and the piece is therefore dipped in nitric acid, specific 

 gravity 1'33, and afterwards rubbed with a long-haired brush. The addition of a 

 little common salt to the dilute sulphuric acid would probably save the use of nitric' 

 acid, which is so apt to produce a new coat of oxide. It is finally made quite dry 

 (after washing in pure water), by being rubbed well with tanners' dry bark, sawdust, 

 or bran. The surface should now appear somewhat depolished ; for when it is very 

 smooth, the gold does not adhere so well. 



3. Application of the amalgam. The gilder's scratch-brush or pencil, made with 

 fine brass wire, is to be dipped into the solution of nitrate of mercury, and is then 

 to be drawn over a lump of gold-amalgam, laid on the sloping side of an earthen' 

 vessel, after which it is to be applied to the surface of the brass. This process- is to 

 be repeated, dipping the brush into the solution, and drawing it over the amalgam, 

 till the whole surface to be gilded is coated with its just proportion of gold. The 

 piece is then washed in a body of water, dried, and put to the fire to volatilise the 

 mercury. If one coat of gilding be insufficient, the piece is washed over anew with 

 amalgam, and the operation recommenced till the work prove satisfactory. 



4. Volatilisation of the mercury. Whenever the piece is well coated with amalgam, 

 the gilder exposes it to glowing charcoal, turning it about, and heating it by degrees 

 to the proper point ; he then withdraws it from the fire, lifts it with long pincers, and, 

 seizing it in -his left hand, protected by a stuffed glove, he turns it over in every 

 direction, rubbing and striking it all the while with a long-haired brush, in order to 

 equalise the amalgam. He now restores the piece to the fire, and treats it in the same 

 way till the mercury be entirely volatilised, which lie recognises by the hissing sound 

 of a drop of water let fall on it. During this time he repairs the defective spots, 

 taking care to volatilise the mercury very slowly. The piece, when thoroughly 

 coated with gold, is washed, and scrubbed well with a brush in water acidulated with 

 vinegar. 



^ If the piece is to have some parts burnished, and others dead, the parts to be bur- 

 nished are covered with a mixture of Spanish white, bruised sugar-candy, and gum 

 dissolved in water. This operation is called in French epargner (protecting). When 

 the gilder has protected the burnished points, he dries the piece, and carries the heat 

 high enough to expel the little mercury which might still remain on it. He then 

 plunges, it, while still a little hot, in water acidulated with sulphuric acid, washes it, 

 dries it, and gives it the burnish. 



6. The burnish is given by rubbing the piece with burnishers of hematite (blood- 

 stone). The workman dips his burnisher in water sharpened with vinegar, and rubs 

 the piece always in the same direction backwards and forwards, till it exhibits a.fine 

 polish, and a complete metallic lustre. He then washes it in cold water, dries it with 

 fine linen cloth, and concludes the operation by drying it slowly on a grating placed 

 above a chafing-dish of burning charcoal 



. 6. The deadening is given as follows : The piece, covered with the protcctioit on 

 those parts that are to be burnished, is attached with an iron wire to the end of 

 an iron rod, and is heated strongly so as to give a brown hue to the epargne by 

 its partial carbonisation. The gilded piece assumes thus a fine tint of gold ; and 

 is next coated over with a mixture of sea salt, nitre, and alum fused in the water 

 of crystallisation of the latter salt. The piece is now restored to the fire, and heated 



