GIG MACHINES

are rotatory drums, mounted with thistles or wire teeth for teazling cloth. See Woollen Manufacture . GILDING ( Dorure , Fr.; Vergoldung , Germ.); is the art of coating surfaces with a thin film of gold. For a full discu ion of this subject, see Gold . Mr. Elkington, gilt toy maker, obtained a patent, in June, 1836, for gilding copper, bra , ., by means of potash or soda combined with carbonic acid, and with a solution of gold. Di olve, says he, 5 oz. troy of fine gold in 52 oz. avoirdupois of nitro-muriatic acid of the following proportions: viz. 21 oz. of pure nitric acid, of spec. grav. 1·45, 17 oz. of pure muriatic acid, of spec. grav. 1·15; with 14 oz. of distilled water. The gold being put into the mixture of acids and water, they are to be heated in a gla or other convenient ve el till the gold is di olved; and it is usual to continue the application of heat after this is effected, until a reddish or yellowish vapour ceases to rise. The clear liquid is to be carefully poured off from any sediment which generally appears and results from a small portion of silver, which is generally found in alloy with gold. The clear liquid is to be placed in a suitable ve el of stone, pottery ware is preferred. Add to the solution of gold 4 gallons of distilled water, and 20 pounds of bicarbonate of potash of the best quality; let the whole boil moderately for 2 hours, the mixture will then be ready for use. The articles to be gilded having been first perfectly cleaned from scale or grease, they are to be suspended on wires, conveniently for a workman to dip them in the liquid, which is kept boiling. The time required for gilding any particular article will depend on circumstances, partly on the quantity of gold remaining in the liquid, and partly on the size and weight of the article; but a little practice will readily give sufficient guidance to the workman. Supposing the articles desired to be gilded be bra or copper buttons, or small articles for gilt toys, or ornaments of dre , such as earrings or bracelets, a considerable number of which may be strung on a hoop, or bended piece of copper or bra wire, and dipped into the ve el containing the boiling liquid above described, and moved therein, the requisite gilding will be generally obtained in from a few seconds to a minute; this is when the liquid is in the condition above described, and depending on the quality of the gilding desired; but if the liquid has been used some time, the quantity of gold will be le ened, which will vary the time of operating to produce a given effect, or the colour required, all which will quickly be observed by the workman; and by noting the appearance of the articles from time to time, he will know when the desired object is obtained, though it is desirable to avoid as much as po ible taking the articles out of the liquid. When the operation is completed, the workman perfectly washes the articles so gilded with clean water; they may then be submitted to the usual proce of colouring. If the articles be cast figures of animals, or otherwise of considerable weight, compared with the articles above mentioned, the time required to perform the proce will be greater. In case it is desired to produce what is called a dead appearance, it may be performed by several proce es: the one usually employed is to dead the articles in the proce of prepared for that purpose, sold by the makers under the term “deading aquafortis,” which is well understood. articles previous to the gilding proce , as is practised in the proce of gilding with mercury, previous to spreading the amalgam, but generally a much weaker solution; or the articles having been gilded may be dipped in a solution of nitrate of mercury, and submitted to heat to expel the same, as is practised in the usual proce of gilding. It is desirable to remark, that much of the beauty of the result depends on the well cleaning of the articles, and it is better to clean them by the ordinary proce es, and at once pa them into the liquid to be gilded. See Gold , towards the end .