Five thousand receipts in all the useful and domestic arts : constituting a complete and universal practical library, and operative cyclopædia / by Colin Mackenzie.

  • Mackenzie, Colin, 1775?-1827.
Date:
1830
Catalogue details

Licence: Public Domain Mark

Credit: Five thousand receipts in all the useful and domestic arts : constituting a complete and universal practical library, and operative cyclopædia / by Colin Mackenzie. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    easily burnished than gold leaf ground with honey as above. Another. The best method of preparing gold powder, is by heating a piepared amalgam of gold, in an open clean crucible, and continuing the strong heat until the whole of the mercury is evapora- ted ; at the same time constantly stirring the amalgam with a glass rod. When the mercury has completely left the gold, the remaining pow- der is to be ground in a Wedgewood’s mortar, with a little water, and afterwaids dried. It is then tit for use. Although the last mode of operating has been here given, the operator cannot be too much i reminded of the danger attending the sublima- : tion of mercury. In the small way here de- scribed, it is impossible to operate without dan- . ger; it is therefore better to prepare it according : to the former directions, than to risk the health by the latter. TO COVER BARS OF COPPER, &C. WITH GOLD, SO AS TO BE ROLLED OUT INTO SHEETS. This method of gilding was invented by Mr. Turner, of Birmingham. Mr. Turner first pre- pares ingots or piece- of copper or brass, in con- venient lengths and sizes. He then cleans them from impurity, and makes their surfaces level, and prepares plates of pure gold, or gold mixed with a portion of alloy, of the same size as the ingots of metal, and of suitable thickness. Having pla- ced a piece of gold upon an ingot intended to be plated, be hammeis and compresses them both together, so that they may have their surfaces as nearly equal to each other as possible ; and then bin ts them together with wire, in order to keep them in the same position during the process re- quired to attach then . Afterwards tie takes sil- ver tilings, which hs mixes with borax, to as-in the fusion of the silver. Thin mixture he lays upon the ed<»e of the plate of gold, and next to the ingot of ractal. Having thus prepared the two bodies, lie places them on a fire in a stove rr furnace, where they remain until the silver and borax placed along tbe edges of the metals melt, and until the adhesion of the gold wi.li the metal is perfect. He then takes the ingot carefully out of the stove. By this process the ingot is plated with gold, and prepared ready for rolling into sheets. TO SILVER COPPER INGOTS. The principal difficulties in plating copper in- gots are, to bring the surfaces of the copper and silver into fusion at the same time ; and to pre- vent the copper from scaling ; for which purposes fluxes are used. The surface of the copper on which the silver is to be fixed must he made flat by filing, and should be left rough. The silver is first annealed, and afterwards pickled in weak spirit of salt ; it is planished, and then scraped on the surface to be fitted on the copper. These piepared surfaces are anointed with a solution of borax, or strewed with fine powdered borax itself, and then confined in contact with each other, by binding wire. When they are exposed to a suf- ficient degree of heat, the flux causes the surfaces to fuse at i he same time, and after they become cold, they are found firmly united. Copper may likewise he plated by heating it, and burnishing leaf-silver upon it; so may iron and brass. This process is called french pla- ting. TO GILD IN COLOURS. The principal colours of gold for gilding are red, green, and yellow. These should be kept in different amalgams. The part which is to remain of the first colour, is to he stopped off with a composition of chalk and glue; the variety requi- red is produced by gilding the unstopped parts with the proper amalgam, according to the usual inode of gilding. Sometimes the amalgam is applied to the sur face to be gilt, without any quicking, by spread- ing it with aquafortis; but this depends on the same principle as a previous quickiag. c a