Gilding

Gilding is the art of adorning a surface by covering it with gold. It was practised by the ancient Egyptians, and is often referred to in the Old Testament. It became common at Rome after the Punic Wars. The various methods now employed fall into three main divisions - mechanical, chemical, and encaustic gilding.

Mechanical Gilding is employed to attach gold leaf to wood, paper, plaster-of-Paris, etc. A wooden picture-frame first receives a coat of oil-paint, and then several coats of whiting mingled with glue, which are successively smoothed with pumicestone and sand-paper. The portion to be burnished is then covered with animal size, while gold-size is applied to the remainder. The frame is now ready to receive the gold-leaf, which is laid on with the broad thin brush named tip, and afterwards made to adhere more closely by means of a softer and thicker brush. When there is much raised ornament, whiting is not used, as it tends to wear away the outline. Two methods are followed in fixing gilt ornaments to a japanned ground. It is either coated with gold-size before receiving the gold-leaf, or isinglass is used to make the gold-leaf adhere. In the latter case a larger part of the surface is covered, and asphaltum is employed to paint the ornament, as it preserves the gold beneath it when the rest is removed by washing. In the "false gilding" now practised in Germany silver-leaf or tinfoil with a coating of yellow varnish is substituted for gold-leaf.

Chemical Gilding. Electro-gilding is now the ordinary means of gilding metals [Electrometallurgy], but other methods are still employed. Wash or fire gilding is effected by applying an amalgam of gold to the surface; the mercury is then volatilised, and a film of gold remains fixed to the metal. Gilding by immersion consists in applying a solution of gold in nitro-muriatic acid, the acid attacking the metal and setting free a corresponding amount of gold, which adheres to the surface. After both of these processes the object is coloured by covering it with a saline composition, and then applying "gilding wax," a mixture of beeswax and ochre, which is afterwards burnt off.

Encaustic Gilding is used for glass, pottery, and porcelain. The gold is precipitated with sulphate of iron or dissolved in aqua regia, the acid being removed by the application of heat. The powdered gold is then mixed with one-twelfth of its weight of oxide of bismuth, and a little borax and gumwater. This mixture is applied to the article with a camel-hair brush, and at first has a dingy colour, but the gold lustre is brought up by burnishing with agate and bloodstone.