GOLD - BEATING; GOLD - BEATERS' SKIN. The peculiar substance called Gold Beaters' Skin is prepared from the outer or peritoneal membrane of the large intestine of the ox, by successive processes of soaking, scra ping, washing, alkalising, 8r.c. The manufacture, called in France (where it is chiefly carried on) boyaaderie, is an exceedingly dirty and offensive one ; but the resulting product is a remarkably fine and beautiful kind of membrane.
Gold beating is a process whereby gold is brought to the state of very fine leaves, for use in various kinds of gilding. The re markable ductility of gold—a quality posses sed by it to a greater degree than by any other known substance—is here taken advantage of to the fullest extent, as a means of limiting the quantity of this costly material required on a given surface.
It is by a combined process of rolling and hammering that the attenuation of the gold is produced. An ingot of gold is milled or rolled, to a thickness of about of an inch ; and this riband is then hammered. The hammering does not take place on the gold itself; but thin membranes are interpo sed between the hammer and the gold. These membranes are of three kinds : an outside covering of common parchment: a set of leaves made of very fine and smooth calf-skin vellum ; and another set made of gold-beaters' skin. The riband of gold is cut up into small pieces, each measuring exactly an inch square ; and 150 of these are beaten or hammered at once, interleaved between the membranes, until they are expanded to nearly four inches square. They are removed, cut into quarters,
replaced between new membranes of gold beaters' - skin, and beaten again ; they again expand to nearly four inches square and are again removed, cut into quarters, and replaced between the skins. A third beating expands them nearly as before. The thickness of the film of gold, by this time, varies from Tz-tylarbiy to of an inch, according to the purpose to which it is to be applied. The attenuation may be rendered more intelligible by stating that 100 square feet of the leaf gold weighs no more than an ounce—a result nearly as surprising as any thing presented in the mechanical arts. A certain greasiness which comes upon the interleaved membranes is removed by beating them between pieces of white paper. The beating of the gold is effected by hammers weighing from 10 to 10 lbs., on a smooth block of marble : 150 small squares of gold form the group or bundle for the first ing, 000 for the second, and SOO for the third.
Two other metals, silver and copper, have sufficient malleability to be brought into the state of thin leaves by hammering ; and both are used to a limited extent in this state in the arts. But these metals would fracture long before such a degree of thinness could be ob tamed as in the case of gold ; consequently leaf. silver and leaf-copper are thicker than leaf gold.