Porcelain and other kinds of earthenware as well as glass may be gilded by mixing a layer of gold in a powdered state by the action of fire. The gold dust or powder required in this opera tion may be obtained by precipitating it from a solution in aqua regia, either by means of sul phate of iron or protonitrate of mercury. In order that the gold powder may be applied to the surface of the article to be gilded it must be well mixed with some viscous vehicle such as spirits of turpentine mixed with some fatty mat ter, or strongly gummed water. It is then laid cn with a fine camel's hair brush. When the article to be gilded is made of soft porcelain, delft-ware, or any kind of earthenware with a plumbiferous glazing, nothing else is required than to apply the gold in this manner, and then subject the piece of earthenware to a heat suffi cient to soften the glazing, and thus fix the gild ing. But in the case of hard porcelain, some kinds of stoneware and other varieties of pot tery, in which the glazing does not soften at a suitable temperature, the gold powder, before being mixed with the viscous vehicle by which it is applied, must have a flux added to it, which serves as a means of attachment between the theta' and the earthenware. The best flux is oxide of bismuth precipitated by water from a solution of nitric acid, with the addition of one-twelfth part of melted borax. One-tenth or one-fifteenth part of this flux is added for every part of gold contained in the mixture, which is applied to the surface of the earthen ware. Heat is applied in the same way as in the previous case to melt the flux, and thus fix the layer of gold to the article. The gilding
must finally be burnished in order to bring up the gold color. Another method of gilding these substances is to mix neutral chloride of plati num with rectified spirits of turpentine in such a manner that the chloride is held in suspension in a finely divided state in the turpentine, to apply this liquid to the article to be gilded by means of a brush, and then to subject the article to heat so as to volatilize the spirits of turpentine and leave a uniform layer of platinum affixed to the glass or earthenware. The article, after being cooled, cleaned with aqua fortis and washed with is next dipped in a gilding liquid; the gilding is then completed by rubbing the gilt parts with chamois leather. This method of gilding has the advantage of enabling the gilder to dispense with the burnishing, which is a very hazardous operation for fragile articles, and in the case of those which are of a very intricate form or very deeply cut out often im practicable.
It was announced in 1912 that the brothers Marino, Italian chemists, had invented a process whereby metals and metallic alloys can be de posited on other metals, ceramic ware, wood, celluloid and other substances by electric agency. In the case of glass, for example, the surface to be metallically mounted is first subjected to sand blasting, to remove the polish and give the metal a grip. This abrased part is then chemically treated, so that when the article is suspended in the electroplating bath, the metal, whether it be of gold, silver or any other metal or its alloy, is attached and forms an integral part of the foundation. See METALLURGY.