Works of art are also produced by other methods; as an example, we will take the process of “spinning or burnishing into form,” which consists in spinning the metal to the desired shape in a lathe, by means of burnishing tools, specially made for the purpose. This process is employed in the production of large bangle bracelets with plain surfaces and other similar works. The metal to be operated upon should be soft and malleable, otherwise the process is very difficult to perform. The disc, or other form of metal, is taken and fixed in the lathe with the aid of holdfasts, a chuck or mould of the desired pattern being provided, upon which the disc is turned by the tools referred to. The metal, as in the other processes, is gradually spun into the required form. In most cases the mould is exactly the shape of the interior of the article required to be made, and under these circumstances it would be made up in several pieces together with a key-piece; so that when this latter is taken away, there is no difficulty in removing the rest, and leaving the article free. It is of importance, during the spinning, to keep the edges free from notches, but should these occur, it would be better to touch them a little with a turning tool. The metal for spinning into a bangle bracelet should be of the form of a flat circular band, soldered of course; it would then be secured upon a properly shaped mould, composed of several pieces, in the manner above described; this would then be placed in the lathe, and the application of the spinning tools would soon bring about the desired form. After the removal of the spun piece of metal, the workman trims the edges up a little, then saws it into two pieces, and at once proceeds to the operations of snapping and jointing, which are delicate processes to perform properly in work of this kind, and require the services of a skilled and competent workman.
Having now described some of the processes in the working of silver, and alluded to the various articles which are produced by wire-drawing; raising with the hammer; stamping; spinning; chasing, &c.; we shall next direct attention to those processes which immediately come after the putting together and soldering the article; and foremost of these is polishing. We trust that the foregoing details in reference to this part of the subject will convey some idea of the art of silver-working.
Polishing is an important process With all precious metal workers. It is applied for the production of surface to their wares, and in proportion to the smoothness required upon the work, so should be the fineness of the material employed in effecting it. The polishing powders are emery, powdered pumice, crocus, rottenstone, putty of tin, and rouge. In the best work, scratches are removed with a smooth and rather soft dark grey stone (Water-of-Ayr stone); it is then polished in the lathe with a stiff brush, and the application of a little fine polishing mixture. We have placed the materials for polishing in their respective order of smoothness or fineness, beginning with emery, which is the coarsest. A very good mixture for ordinary work consists of equal portions of emery, pumice, and crocus, with oil added to the consistence of a thick paste. Good work does not want much polishing, for the beauty of it depends more on its being executed by a well-trained workman; whereas rough and badly executed work requires much polishing, and for this the coarser powders are preferable, or a mixture of them; but for the smoother work the finer powders should be employed.
The Water-of-Ayr stone employed for polishing is usually obtained in the form of small square sticks, and is used with a small quantity of water to the surface of the work, in a similar manner to filing. The stone is softer than the material upon which it operates (and, in fact, so are all the materials for polishing), and therefore wears away, producing a mud-like substance upon the article, which should be repeatedly removed in order to ascertain the progress made. This may be done with a piece of clean rag, or tissue-paper. When the work is polished at the lathe it will gradually become enveloped in grease, &c., which should be removed occasionally, to show when the process has been carried far enough. The polishing of silver work is a branch of the trade commonly performed by girls. It is hard work for them, as the metal possesses a very soft nature; it therefore pulls hard against the brush which holds the polishing mixture. The lathe employed is the ordinary polishing lathe with a horizontal spindle, and is worked with a common foot-treadle; steam-power is used by some firms for moving these lathes, but it is by no means the usual custom at present.
After the completion of the polishing process, the work is well washed out in a prepared solution, to remove the mixture which adheres to it; a solution of soda is found to answer the purpose best, both from its cheapness and effectiveness. It should be used hot, with the addition of a little soap, and with a stiff brush the dirt is soon removed. The quantity of soda used to a given proportion of water differs in the trade, and there is no set rule to go by; it depends, more or less, upon the adhesiveness of the polishing mixture. We have found about two ounces of it to a quart of water amply sufficient for the purpose.
Enriching the Surfaces of Silver.