GOLDBEATING. The art of goldbeating is of great antiquity, being referred to by Homer; and Pliny states that one ounce of gold was extended to 750 leaves, each leaf being four fingers square, which is three times the thickness of the ordinary leaf gold of the present time. The ancient Peruvians made very thin sheets of gold, and nailed them together on the walls of their temples of worship; on the coffins of the Theban mummies specimens of original leaf-gilding are met with where the gold is in so thin a state that it resembles modern gilding. The art seems to have been practised in India, judging from the rude specimens of gilding at Tippo Saib's palace at Bangalore.
In modern times it has been practised in the capitals of the principal commercial countries of Europe. In England it was confined to London until within the present century. It has been introduced into Scotland and the United States of America within that period. It is now practised in several towns in England, and to a small extent in Ireland, at Dublin only.
The manufacture being attendant upon an advanced state of the arts, it is only found in old established countries, and is not yet practised in any of the British colonies.
From the existence here of some now obsolete-fashioned tools, similar to those at present in use at Paris, it would appear to have travelled to England from that quarter. The art has nowhere been so perfected as in London; but of late years, from intercourse with English goldbeaters, efforts have been made on the Continent, with the aid of English goldbeaters' skin, to rival the extreme fineness of the English product.
The ordinary size of a leaf of gold is 3 inches and 3-8ths, for the production of 2000 leaves of which from 18 to 19 dwts. of gold were allowed to the workman fifty years since in London, but now, owing to the improvement in the quality of the skin and superior skill on the part of the workmen, not more than an average of 16 dwts. are required, and with very skilful workmen it is sometimes accomplished with 14 dwts. This, however, is not to be taken as any test of the extreme malleability of gold; it is only the point to which it is desirable to attain for commercial purposes.
Experiments have been made to ascertain to what degree of thinness gold and silver could be reduced: it was found that one grain of gold was spread to the extent of 75 square inches, and the same weight of silver to the still more extraordinary dimension of 98 square inches. Taking one
cubic inch of gold at 4900 grains, it will be found that the gold was the 367,650th part of an inch in thickness, or about 1200 times thinner than ordinary printing paper. Thus, if this number of leaves of gold were placed on one another, they would constitute a pile an inch high; the same number of leaves of paper would form a pile half the height of the Monument of London. The silver, though spread over a much larger surface, was thickest, owing to the difference in its specific gravity; but, calculated by weight, silver is the most malleable metal with which we are acquainted, considerably exceeding that of gold. This experiment does not, however, determine the extent of the malleability of either metal, as the means employed to test it were found to fail before there was any appearance of the malleability of the metals being exhausted.
The gold used by the goldbeater is variously alloyed according to the variety of colour required. Fine gold is commonly supposed to be incapable of being reduced to thin leaves. This is an error. It is objectionable for commercial purposes on account of its greater cost. It also adheres on one part of a leaf touching another, thus causing a waste of labour by the leaves being spoiled; but for work exposed to the weather it is much preferable, as it is more durable, and does not tarnish or change colour.
The specimens of gold leaf exhibited by Mr E. S. Marshall, goldbeater of London, at the Great Exhibition of 1851, and for which the prize medal was awarded to him, were twelve in number, and embraced a regular gradation in colour from red down to nearly white, viz.—red, pale red, extra deep, deep, orange, lemon, deep pale, pale, pale pale, deep party, party, and fine gold. The deeper colours were alloyed with from 12 to 16 grs. of copper per oz., but without any silver, as any alloy of silver with this quantity of copper would considerably impair the malleability. The middle colours contained from 12 to 20 grs. of silver, and from 6 to 8 grs. of copper to the ounce; the paler golds contained from 2 to 20 dwts. of silver to the ounce, but no copper, for the same reason that the silver was omitted in the red golds.
The process of goldbeating is thus conducted. The gold having been alloyed according to the colour desired, it is melted in a crucible, at a higher temperature than is simply necessary to fuse it, as its malleability is improved by exposure to a greater heat; sudden cooling does not interfere with its malleable properties, differing in this property from some other metals. It is then cast into an ingot, and flattened into a ribbon of inch wide and 10 feet in length to the ounce. After being flattened it is annealed and cut into small pieces of about 6 grs. each, and placed between the leaves of a cutch, which is about half an inch thick and inches square, containing about 160 leaves of a tough paper manufactured in France. Formerly fine vellum was used for this purpose. The cutch is beaten on for about 20 minutes with a 17-pound hammer, which rebounds by the elasticity of the skin, and saves the labour of lifting, by which the gold is spread to the size of the cutch; each leaf is then taken out, and cut into four pieces, and put between the skins of a shoder inches square and th of an inch thick, containing about 700 skins, which have been worn out in the finishing process. The shoder requires about two hours' beating upon with a 9-pound hammer. As the gold will spread unequally, the shoder is beaten upon after the larger leaves have reached the edges. The effect of this is, that the larger leaves come out of the edges in a state of dust. This allows time for the smaller leaves to reach the full size of the shoder, thus producing a general evenness of size in the leaves.
Each leaf is again cut into four pieces, and placed between the leaves of a mould composed of about 900 of the finest skins, five inches square and three-quarters of an inch thick; this is the last and most difficult stage of the process; and on the fineness of the skin and judgment of the workman the
perfection and thinness of the leaf of gold depend. During the first hour the hammer is allowed to fall principally upon the centre of the mould. This causes gaping cracks upon the edges of the leaves, the sides of which readily coalesce and unite without leaving any trace of the union after being beaten upon. At the second hour, when the gold is about the 150,000 of an inch in thickness, it for the first time permits the transmission of the rays of light. In pure gold, or gold but slightly alloyed, the green rays are transmitted; and in gold highly alloyed with silver the pale violet rays pass. The mould requires in all about four hours' beating with a 7 lb. hammer, when the gold will have arrived at the ordinary thinness for the gold leaf of commerce. It is then taken out of the mould, and the rough edges are cut off by slips of the rattan fixed in parallel grooves of an instrument called a waggon, the leaf being laid upon a leathern cushion for that purpose. The leaves thus prepared are placed into a book capable of holding twenty-five leaves each, which have been rubbed over with red ochre to prevent the gold clinging to the paper, and is used for gilding picture-frames, books, and for numerous other ornamental purposes.
The dryness of the cutch, shoder, and mould is a matter of extreme delicacy. They require to be hot-pressed every time they are used, although they may be used daily, to remove the moisture which they acquire from the atmosphere, except in extremely frosty weather, when they acquire so little moisture that then a difficulty arises from their over-dryness; the brilliancy of the gold is diminished, and it spreads very slowly under the hammer. On the contrary, if the cutch or shoder be damp, the gold will become that which is technically termed hollow or sieve-like; that is, it is pierced with innumerable small microscopical holes; and in the moulds in its more attenuated state it will become reduced to a pulverulent state. This condition is more easily produced in alloyed golds than in fine gold.
It is necessary that each skin of the mould should be rubbed over with calcined gypsum (the fibrinated variety) each time the mould may be used, in order to prevent the adhesion of the gold to the surface of the skin in the process of beating.
Dentist gold is gold leaf carried no farther in the process than that of the cutch, and should be perfectly pure gold.
By the above process silver is beaten, but not so thin, the inferior value of the metal not rendering it commercially desirable to bestow so much labour upon it. Copper, tin, zinc, palladium, lead, cadmium, platinum, and aluminium can be beaten into thin leaves, but not to the extent of gold or silver.
Shell Gold, used in painting and illuminating, is made by grinding gold leaves with honey, and afterwards separating the honey from the powdered gold by means of water. When the honey is washed away, the gold may be put on paper or kept in shells. When used, it is commonly diluted with gum-water. The German gold powder, prepared in this manner from the Dutch gold leaf, is generally used; and when it is well secured with varnish, it answers the end in japanners' gilding tolerably well.