GOLD-BEATING is the art of reducing gold to extreme ly thin leaves, for the purposes of gilding. The gold em ployed for this purpose must he pure. It should be melt ed in a crucible, with a small quantity of borax, and cast into small bars, or thin flat ingots, about Iths of an inch wide, and weighing two ounces each. These are extend ed to long plates, by rolling them in a flatting-mill, until they become lengthened out like ribbands, and very thin. To effect this, the ingot must be passed between the rol lers a great number of times ; and to correct the hardness which the repeated rolling at length produces, the metal must be occasionally annealed, by heating it to redness, and suffering it to cool gradually.
The rollers employed for this process should be of a most perfect cylindrical figure; and have a highly polished surface. They should he of a large size, that they may not yield or bend ; for the ultimate perfection of the gold leaf depends very materially upon the precision with which every part of the ribband is reduced to an equal thickness. Formerly the reduction was wholly effected by hammer ing: in course of time, a small hand flatting-mill was used to finish the work, after a considerable extension had been produced by the hammer; but at present the most improv ed practice is to have the rolling done at a flatting-mill, where, by following a similar process to that which we have described under the article COINING, a ribband can be produced which will contain very nearly the exact weight required for a given surface. The gold-beater ge nerally orders this to be at the rate of very nearly 62 grains to a square inch ; and the workman who conducts the rolling, shews his care in coming as near to this as possi ble. Still much depends upon the goodness of his machi nery, and also upon the regularity of the ingots in the first instance.
The moulds for casting the ingots should be made of cast-iron, and the internal surface rather concave, because, in cooling, the metal contracts more in thickness at the centre than at the outside. The moulds are heated, and rubbed with linseed oil, or tallow, on the inside, previous to pouring in the metal.
The ribband being thus prepared, the gold-beater cuts it up with shears into small squares of an inch each, and having previously divided it rather accurately by com passes, the pieces will all be very nearly of an equal weight, which is about 61 grains for the ordinary gold leaves, but is more or less, as the leaves are intended to be thicker or thinner. In order to beat out these squares to greater extent, they are made up into a parcel of about 150, with a leaf of fine calf-skin vellum interposed be tween each square, and about 20 leaves extra at the top and bottom of the parcel. The vellum leaves are about four inches square, and the plates of an inch square are carefully laid in the centre. In order to retain the packet together, it is thrust into a case of strong parchment, which is open at each end, so that it is only a belt or band, but sufficiently broad to cover the whole packet, except the two ends ; and to secure these, a second case is drawn over the packet in the opposite direction. By this means the packet is rendered sufficiently firm and compact to bear beating with a large hammer of 15 or 16 pounds weight, the face of which is circular, nearly four inches diameter, and so much convex as will make it strike more forcibly upon the centre of the square packet, and extend the small square plates regularly.
The beating is performed upon a very strong stool, or bench, framed to receive a block of marble, or other hard stone, which is about nine inches square on the surface, and as heavy as can be procured ; the wood-work is car ried up round the stone in the form of a ledge, rising on the two sides and at the back ; and to the front edge is nailed a kind of apron, which the workman takes before him, to preserve any fragments of gold which may come out of the packet. The handle of the hammer is very short, and the workman manages it with one hand: he strikes fairly upon the middle of the packet, which he fre quently turns over to beat the opposite side, but this he does in the interval between two strokes, without losing his blow. He keeps tip a constant beating, and when fa tigued with one hand he dexterously changes the hammer to the other, whilst the hammer is elevated in the air, and without any loss of time or force. The packet is occa sionally bent, or rolled between the hands, to loosen the leaves, and render the extension of the gold more free; and the packet is sometimes taken to pieces to examine the gold, and the centre leaves put at the outside, by which means the spreading of the gold will be equal throughout the packet. The beating is continued until the gold plates are increased to nearly the same size as the pieces of vellum ; they are then taken out of the packet, and each cut into four squares, by a knife drawn • across them in two directions. This reduces the plates to about the same size as at first, and they are again made up for a second beating, in a packet of about the same thick ness as the former ; but instead of vellum, skins about five inches square, prepared from the intestines of an ox, are interposed between each. The packet is made up in cases in the same manner as before described. The second beating is performed with a smaller hammer, of about ten pounds weight, and is continued until the leaves are ex tended to the size of the skins. The folding of the packet must be frequently repeated during this beating, to leave the gold as free as possible between the skins; because the leaves begin now to be very delicate, and are easily broken, if the beating is not very carefully performed. The leaves are spread upon a cushion, and again divided into lour, by means of two pieces of cane cut to very sharp edges, and fixed upon a board, crossing each other at right angles. This cross being applkd upon each square leaf, and pressed upon it, will divide it into our equal portions, which are made up into a third packet of convenient thickness, and more extended to the size of the in tended leaves, which is about three inches, or three and a half square. In this state the leaves will be extended to 192 times the surface which the plates had before the beat ing was begun. As these plates were each an inch square, and 75 of them weighed an ounce, the surface of the ulti mate leaves will be 192 X 75= t4400 square inches, or 100 square feet per ounce. This is by no means so thin as they may be made, for it is very practicable to extend an ounce to 160 square feet ; but the waste arising from the great number of broken leaves, and the increase of labour, renders it of very little advantage to the gold-beater to reduce them to a greater thinness; and to the gilder such thin leaves are less valuable, both because they make less durable work, and are so liable to break and waste in lay ing them on.