Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/777

Rh being exhausted. In practice the average degree of tenuity to which the gold is reduced is not nearly so great as the example above quoted. A “book of gold” containing 25 leaves measuring each 31} inches, equal to an area of 264 square inches, generally weighs from 4 to 5 grains.

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, however, is not the case, although its use for ordinary purposes is undesirable 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 external gilding on many public build- ings, such, e._r/., as the Albert Memorial in Hyde Park, London, is done with pure gold. The following is a list of the principal classes of leaf recognized and ordinarily prepared by British beaters, with the proportions of alloy per ounce they contain.

=*'=""° 0‘ 1”‘ ’).’§‘r’‘’a‘’('§i.'1‘.’‘' §i°s‘i?5t-'9." l(if08(?}lit;)ltl')Il‘i Grains. Grains Grains. Red .............................. .. -156460 20-24 Pale red ......................... .. 46-1  16 Extra deep ..................... .. 456 12 12 Deep ............................. .. 4-14 24 1'2 Citron ........... . .............. .. -140 30 10 Yellow........ ................... .. 408 72 Pale yellow ..................... .. 384 96 Lemon ........................... .. 360 1:20 Green or pale ................... .. 312 1 (18 White .......................... .. ‘.240 240

{{11fine|The process of goldbeating is thus conducted. The gold, having been alloyed according to the colour desired, is melted in a cru- cible, 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 11ot interfere with its malleable properties, gold differing in this respect from some other metals. It is then cast into an ingot, and ﬂattened, by rolling between a pair of powerful smooth steel rollers, into a ribbon of 1% inch wide and 10 feet in length to the ounce. After being flattened it is annealed and cut into pieces of about 6.13 grs. each, or about 75 per ounce. and placed between the leaves of a “ cutch," which is about half an inch thick and 35 inches square, containing about 180 leaves of a tough paper manufactured in France. Formerly tine vcllmn was used for this purpose, and generally still it is interleaved in the proportion of about one of vellum to six of paper. 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," 45 inches square and iths of an inch thick, containing about 720 skins, which have been worn out in the finishing or “mould” 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 margins of larger leaves come out of the edges in a state of dust. 'l‘his 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 950 of the tiniest gold-bcaters’ skins, five inches square and three-quarters of an inch thick, the contents of one shoder filling three moulds. The material has now reached the last and most dillicult stage of the process; and on the ﬁneness of the skin and judgment of the workman the perfection and thin- ness 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 150,000tl1 part of an inch in thickness, it for the first time per- mits 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’ heating with a 7-pound hammer, when the ordinary thinness for the gold leaf of commerce will be reached. A single ounce of gold will at this stage be extended to 75x4 x 4=1200 leaves, which will trim to squares of about 3} inches each. The ﬁnished leaf is then taken o11t of the mould, and the rough edges are trimmed off by slips of the ratan ﬁxed in parallel grooves of an instrument called a waggon, the leaf being laid upon a leathern cushion for that pur rose. The sizes to which British leaf .is cut are 3, 35,, 35, 3%, an 3.1,; inches. The leaves thus prepared are placed into “books” capable of holding 25 leaves each, which have been rubbed over with red ochre to prevent the gold clinging to the paper. The leaf is used for gilding picture-frames, and for other ornamental purposes. See .}}

The fine membrane called goldbeaters’ skin, used for making up the shoder and mould, is the outer coat of the caecum or blind gut of the ox. It is stripped off in lengths about 25 or 30 inches, and freed from fat by dipping in a potash solution and scraping with a blunt knife. It is afterwards stretched on a frame ; two membranes are glued together, treated with a solution of aromatic substances or camphor in isinglass, and subsequently coated with white of egg. Finally they are cut into squares of 5 or 5% inches ; and to make up a mould of 950 pieces the gut of about 380 oxen is required, about skins being got from each animal. A skin will endure about 200 beatings in the mould, after which it is ﬁt for use in the shoder alone.}}

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 atmo- sphere, except in extremely frosty weather, when they acquire so little moisture that then a diﬁiculty arises from their over-dryness, whereby 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 micro- scopical holes; and in the moulds in its more attenuated state it will become reduced to a pulverulent state. This condition is more readily 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 pre- vent the adhesion of the gold to the surface of the skin in beating. Dentist gold is gold leaf carried no further than the cutch stage, and should be perfectly pure gold.

By the above process also silver is beaten, but not so. thin, the inferior value of the metal not rendering it com- mercially 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 same extent as gold or silver.

 GOLD AND SILVER LACE. Under this heading a general account may be given of the use of the precious metals in textiles of all descriptions into which they enter. That these metals were used largely in the sumptuous textiles of the earliest periods of civilization there is abund- ant testimony; and to this day, in the Oriental centres whence a knowledge and the use of fabrics inwoven, orna- mented, and embroidered with gold and silver first spread, the passion for such brilliant and costly textiles is still most strongly and generally prevalent. The earliest mention of the use of gold in a woven fabric occurs in the description of the ephod made for Aaron (Exod. xxxix. 2, 3)—“ And he made the ephod of gold, blue, and purple, and scarlet, and fine twined linen. And they did beat the gold into thin plates, and cut it into wires (strips), to work it in the blue, and in the purple, a11d in the scarlet, and in the ﬁne linen. with cunning work.” In both the Iliad and the 0:./yssey distinct allusion is frequently made to inwoven and embroidered golden textiles. Many circumstances point to the conclusion that the art of weaving and embroidering with gold and silver originated in India, where it is still principally prosecuted, and that from one great city to another the practice travelled westward,—Babylon, Tarsus, Baghdad, Damascus, the islands of Cyprus‘ and Sicily, Con-.