Gold-Beating , the process of hammering gold into thin leaves. It is not known what were the methods in use by the Egyptians, Greeks, and Romans for obtaining the thin leaves they manufactured; but it is probable that they did not differ essentially from the simple processes now practised, which were brought to their present perfection by continued experience and the application of a moderate degree of skill. The earliest recorded notice of the mode of preparing gold leaf is that of the German monk Theophilus, in or before the 12th century, from which it appears that parchment was used as a covering to the gold during the hammering, and the leaves were prevented from sticking by the application of red ochre or chalk. When the substance called gold-beaters' skin (French, baudruche) was first used for the production of the finest qualities of gold leaf is not known. This material, essential to the manufacture, is derived from the caecum of the ox, which, being well cleaned, is doubled together, the two mucous surfaces face to face, in which state they unite firmly. The membrane is then treated with solutions of alum, isinglass, white of eggs, etc, and sometimes with creosote, and, being beaten between folds of paper to expel the grease, is finally pressed and dried.
The leaves thus obtained, each 5 1/8 in. square, are made up into moulds, each composed of 850 leaves. The caeca of 500 oxen are required for a single mould. - Various qualities of gold are employed for gold leaf. The common coin answers a very good purpose, and different shades of color are obtained, according to the proportions of silver and copper in the alloy. Chemically pure gold makes leaves well adapted for gilding which is to be exposed to the weather, as they are less liable to tarnish or change color; these are remarkable for their property of adhering as they touch each other. Deep red colors are obtained by alloys of 12 to 16 grains of copper to the ounce of gold; silver, if added when too much copper is present, lessens the malleability of the alloy. Medium colors, as orange, lemon, etc, result from the alloy of 12 to 20 grains of silver and 6 to 8 of copper to the ounce; and pale colors from alloys of from 2 to not less than 20 pennyweights of silver to the ounce, without copper. The gold, being melted in a crucible with a little borax, is cast into ingots, commonly 3 or 4 in. long, 3/4 in. wide, and about 1/2 in. deep, and weighing about 1,000 grains each.
The ingots are annealed in hot ashes to remove the grease derived from the moulds and increase the malleability of the metal. The French then forge the metal upon an anvil with small hammers, reducing its thickness to one sixth of an inch, and at the same time exposing it to frequent annealings; but this is omitted by the English, who submit it at once to the lamination process, or rolling between two rollers of polished steel, which are adjusted so as to be brought successively nearer together. This operation, which formerly reduced the gold to a ribbon an inch wide and 1/25s of an inch thick, is by improved machinery now extended till the gold is reduced to a sheet a little more than 1/800 of an inch thick, an ounce making 10 ft. in length by 1 1/2 in. in width. The gold, again annealed, is next cut up into inch squares, the weight of each being about 6 grains. About 150 of these pieces are piled alternately with leaves of line calf-skin vellum or of a tough paper manufactured in France for this purpose, each piece being placed in the middle of one of the leaves, which are 4 in. square. A number of extra leaves are added to the top and bottom of the pile, which when completed is called a tool or kutch.
This is then slipped into a parchment case, open at two ends, and this into a similar case, so as to enclose the pack on all four sides. The pack is now placed upon a block of marble, set for an anvil, with a ledge around three sides of it, and a leather apron for the fourth side, which is held up by the workman, who proceeds to beat the pack. He wields a 16-lb. hammer, shifting it from one hand to the other without interfering with the regularity of the stroke, also occasionally turning the pack with the same dexterity. The hammer has a slightly convex face, which adds to its efficiency in spreading the gold, and the working of it is made much easier by the elasticity of the pack causing it to rebound. The pack is from time to time bent back and forth to overcome the adhesion between the gold and the vellum or paper; it is also rolled between the hands for the same purpose; and it is occasionally opened to examine the condition of the leaves and properly arrange them. In about 20 minutes' beating the gold is spread to the size of the leaves, covering 16 square inches in place of one inch.
The pieces are then taken out, and each is cut into four square pieces, the original 150 pieces being thus increased to 600. These are again packed, this time in gold-beaters' skin, again enclosed in parchment cases, and beaten with a smaller hammer, till they are extended to the size of the skins. This operation requires about two hours. More particular care is given now than before to folding the pack in order to loosen the leaves. When all the gold leaves have expanded to the full size, they are taken out and spread by the breath one by one upon a cushion, where each is cut into four squares by two sharp edges of cane fixed crosswise, and used by pressure downward. To this material the thin leaves do not adhere as they do to a steel blade. The squares are now 2,400 in number. These are once more packed, making three parcels, and beaten as before for four hours. This part of the process requires the most skill and care from the workman. The skins are the finest, about 5 in. square; the leaves are brought at the end of the operation to 3 or 3 1/2 in. square. In this condition an ounce of gold is made to cover 100 sq. ft. It begins to transmit the rays of light, and, if slightly alloyed, the green rays particularly, but, if highly alloyed with silver, the pale violet rays also.
The beating may be continued, and the gold be reduced to the thinness of the specimens noticed in Gilding; but there is no advantage gained in passing the average of the commercial gold leaf, which is about 1/200,000, or that of the French, which is probably less than 1/280,000 of an inch thick. The leaves are sorted after the final beating, each one being lifted by a delicate pair of whitewood pincers, and spread out by the breath upon a leather cushion. It is then trimmed down to about 3 1/4 in. square by a square frame of sharp cane, and laid between the leaves of the book in which it is sold. Each book is made to contain 25 gold leaves, and these are prevented from adhering to the paper by an application to this of red ochre or red chalk. - Silver and copper are both beaten into leaves; but their value is not so great as to render it an object to reduce them to anything like the tenuity of gold leaf, if their malleability admitted of its being done.