3S1 



GILDIXG. 



GILDING. 



392 



with the acid, with the production of considerable heat. This solution 



name of this liquid has caused the appellation of water-gilding to be 

 given to that which would more properly be called metal-<jildin<t. 

 When it is uncontaminated by the presence of any foreign substance, 

 the '' quick-water " is white and pellucid. 



When a piece of copper or brass is immersed in or brought in contact 

 with this solution, its surface is immediately converted into an amalgam. 

 To this amalgamated surface mercury and gold amalgam closely adheres, 

 by means of the molecular attraction of the particles of the fluid metals 

 for each other. 



The manner in which this agent is applied in practice varies according 

 to the kind of articles about to be gilt. If they are small, strong, and 

 to be gilt all over, as copper buttons, buckles, and rings, a quantity 

 of them, which should not exceed three or four pounds in weight, 

 is put into a deep glazed earthen pan or " jowl ; " to these are added 

 about three or four tea-spoonfuls of the " quick-water," together with 

 the requisite portion of amalgam. The whole is then thoroughly 

 stirred with a brush or stick, till the amalgam entirely covers the 

 surface of every article, more particularly the indentations and sunken 

 parts, which are the last to receive a coating, from their being less 

 exposed to the contact of the fluids. When they are completely 

 covered, they are by some gilders rinsed in cold water and dried by 

 shaking in a bag of warm sawdust ; while by others this part of the 

 process is postponed to a later period of the operation, and they are 

 put, in their wet state, with the generated nitrate of copper still hanging 

 about them, into the gilding-cage. This cage is made in a cylindrical 

 form, and is generally about 18 inches in length by 9 or 10 in diameter. 

 It is formed of coarse iron-wire gauze, supported by an external frame- 

 work of iron, and furnished with a solid iron door at one extremity, 

 which generally forms a sector of one-third of the circular end. It is 

 provided with an axle, which extends to a length of about 3 feet from 

 the end at which the door is placed, and is there terminated by a winch, 

 and to a distance of 5 or 6 inches in the opposite direction. The 

 articles under process of gilding are placed in this cage, and the door 

 of it securely fastened ; it is then suspended by its axle on two supports 

 in an iron cylinder, which somewhat resembles a gas retort, and which 

 is in a similar manner fixed into brickwork over a furnace or stove. 

 The cylinder being previously heated by a coal fire beneath it, to such 

 a degree as to be red-hot over a large proportion of its inferior surface, 

 the cage is introduced, and the doors of the cylinder closed. The 

 heated air contained within the cylinder soon raises the temperature 

 of the substances immersed in it ; and as the cage is kept continually 

 revolving by means of the winch, which projects through an aperture 

 in the doors, they have all an equable share of heat, and allow of a 

 nearly equal evaporation of the mercury from all their surfaces. The 

 farther extremity of the cylinder communicates with a chamber, which 

 is in general built of masonry and plastered over all the internal sur- 

 faces. The floor of this chamber is covered to a depth of about two 

 feet with cold water, which on coming into contact with the mercurial 

 vapours condenses a portion of them, and causes them to return to the 

 liquid form. If this condenser, however,} were made quite close, a 

 great portion of the mercurial vapour would return through the 

 cylinder into the apartment or gilding shop, and thus not only be 

 wasted, but materially injure the health of the persons engaged in the 

 work. A communication extending obliquely upwards, and made of 

 one or more ranges of iron stove-piping, is therefore connected with a 

 second smaller condenser on the story above, and this is again re- 

 peated a third or perhaps a fourth time. A current of heated air is 

 thus continually ascending from the lowest condenser, and establishes 

 a perpetual draught through the cylinder, thus preventing the dele- 

 terious mercurial vapour from mixing with the atmosphere of the shop 

 in which the work is going forward ; some of the vapour is, however, 

 necessarily wasted by this precaution. The condensers are opened 

 at intervals of several months, and the quicksilver taken out, washed, 

 and dried ; it is lometimes found necessary again to. distil it, to free 

 it from all impurities. 



After the cage, with its contents, has been in the cylinder for a 

 length of time varying, according to the temperature at which it has 

 been kept, from five minutes to a quarter of an hour, the mercury will 

 be found to have entirely evaporated from the gilt surfaces. If the 

 articles have been previously washed and dried, they will appear of a 

 clear yellow colour ; and they may be allowed to remain in the cylinder, 

 the cage revolving as before, until they are sufficiently heightened 

 in tint. If they have not been so treated previously, they will 

 appear of a dark, soiled, dirty colour, being covered with an incrusta- 

 tion of oxide of copper and of iron, and other impurities. To remove 

 these, the goods are taken out of the cage ; and after being allowed to 

 conl for a few minutes, they are thrown, while still warm, into weak 

 <juir:k-water, that is, diluted nitrate of mercury. This converts the 

 gold again into amalgam, owing to the precipitation of a portion of the 

 mercury by the copper, which is taken up with avidity by the gold. 

 They are then washed with clean water, dried in warm sawdust, and 

 again committed to the cage and cylinder, which, by the evaporation of 

 the mercury, give them a clean colour. They may then be heightened, 

 which is done by continuing to revolve them at the same high tempera- 



ture within the cylinder, occasionally shaking them together, that they 

 may all have an equal share of the heat. The end intended to be 

 effected is a partial oxidation of the surface of the gold, caused by 

 means of the increased temperature of the metal goods after the 

 mercury has evaporated, and which remains unaffected by nitric or 

 sulphuric acids after the slight film of oxide of copper has been instan- 

 taneously removed by their action. This partial oxidation occasions a 

 slight difference of colour, which is perceptible to an experienced 

 eye, and confers on the gold a degree of that orange colour which is so 

 generally admired in golden and gilt articles. 



Buttons and articles of a similar description are often gilt only on 

 their tops, or on some other portion of their surfaces ; while the 

 remainder is left uncovered with gold, and of the native colour of the 

 metal of which they are manufactured. This is accomplished in the 

 mode described under BUTTON MANUFACTURE. 



Many descriptions of articles would be injured or destroyed by the 

 method of gilding just now described. Such are all those which are 

 of considerable dimensions in proportion to the thickness of the metal 

 out of which they are made ; as well as those whose individual weight 

 and extent of surface would expose them to such attrition from the 

 rotatory motion of the cage as would occasion the gold laid on to be 

 entirely or partially nibbed off in the process of its application. 

 Besides this, there is in thin and fragile articles an imminent danger 

 of their being broken when they are amalgamated and rendered brittle 

 throughout a great part of their substance by the necessary immersion 

 in the quick-water. To obviate the inconveniences that might hence 

 result, a different method is employed, so far as regards the mechanical 

 part of it, though the chemical principles on which it depends are 

 precisely the same. Articles of this description are most commonly 

 gilt only on one side. There are two modes of preventing the amalgam 

 from adhering to those parts of the surface that are intended to be 

 left bare. One is to lacquer those parts, and after the spirit of wine 

 is thoroughly evaporated, to immerse them in the quick-water, and 

 afterwards apply the amalgam ; the gummy surface left behind by the 

 lacquer is entirely unaltered by its contact with the mercurial solution ; 

 but its exposure to the high temperature necessary in the subsequent 

 parts of the process chars the gum, blackens it, and causes it to peel 

 off. The other mode of applying the gold is to distribute the quick- 

 water over the parts requiring it by a small brush or camel's hair 

 pencil, and these then have the amalgam applied as before ; if, as is 

 sometimes the case, the goods are to be entirely covered, they are 

 immersed at once in the quick-water. The goods thus prepared are 

 laid with the gilt surfaces uppermost on an open iron pan, of a shape 

 something like that of a frying pan, which is held over a coke fire. 

 The chitnuey is made wide at the bottom, and narrows rapidly as it 

 proceeds upwards, so as to collect as much as possible of the mercurial 

 vapour, for the recovery of which no effort has hitherto been made. 

 A great proportion however necessarily escapes into the apartment, 

 and renders this mode of gilding much more unhealthy than the use of 

 the cylinder and cage. As the mercury gradually evaporates from 

 their surfaces, their position is changed, when requisite, by means of a 

 short pair of tongs ; and when entirely free from it, the process of 

 quick-watering is performed. 



Where the cylinder is employed, it is usually swept out daily, before 

 the fire has heated it in the morning. A portion of the gold amalgam 

 is rubbed off by the attrition of the cage, and falls on the interior 

 surface of the cylinder, whose heat melts it wholly or partially, and it 

 becomes mixed with the oxide of iron that is constantly in course of 

 production by the elevated temperature of the cylinder. This being 

 carefully collected and refined, is found to yield an average of about 

 l-30th of the gold employed, to which dividend the richer sorts have 

 contributed from their superabundance a greater proportionate quantity 

 than the commoner qualities. 



Gilt articles of all the better qualities are submitted to an after- 

 process called colouring, for the purpose of conferring on them a deeper 

 orange tint than is natural to the gold itself, or can be obtained by the 

 process of heightening already mentioned. The principle of this 

 additional operation is always the same, though the methods resorted 

 to differ greatly from each other. One of the compositions employed 

 for this purpose is formed of twenty-four pafts of nitrate of potash, ten 

 of sulphate of alumina, five of sulphate of iron, and five of sulphate of 

 zinc, boiled together in water, thoroughly mixed, and cooled without 

 being allowed to crystallise. This mixture is formed into a thin paste 

 with water, which is spread over the surfaces of the articles by their 

 being immersed in it ; and when they are placed on a heated iron plate, 

 the warm gold surfaces become oxidised. A mixture is sometimes 

 made of bees' wax and yellow ochre, which being rubbed over the 

 gilt surfaces and burnt off, occasions on a similar principle the same 

 result. Goods that are to appear bright are scratched over before 

 colouring with a brush made of fine brass wire. 



Most gilt articles are burnished by a stone burnisher, formed of a 

 polished piece of black haematite. This is fixed into a proper handle. 

 Small articles, as buttons, &c., are placed in a lathe, and the stone 

 applied to them as they revolve ; those that do not admit of this are 

 burnished by hand on a table or bench. 



Besides copper and brass, several other substances admit of being 

 gilt. Silver is gilt in a manner similar to that above described. Steal 

 and iron are gilt by being immersed in a mixture of the nitro-nmriat 



