Fig. 40. Scratch-brush Lathe.

The finishing of silver work requires some little knowledge and skill to perform it properly; and we think that a few observations bearing upon it will be of service to those for whom this manual is written. After either of the processes of whitening or plating, the work has to be scratched, unless required to be left a dead white, then this process does not take place; the scratching removes from the surface the dull white colour produced by the above processes, and effects a characteristic bright and uniform colour to the work of the silversmith. Scratching is done at the lathe ([Fig. 40]) by the application of a very fine brass-wire brush of circular form running upon the spindle; a solution of weak ale runs from a barrel with a tap to it, placed upon the framework of the lathe so as to enable the beer running from it to fall upon the brush during the whole time of its rotary action, and this assists the brush the more easily to glide over the surface of the work submitted to it. A large quantity of silversmith’s work receives no other treatment than this, after the whitening processes have taken place. Silver chains are burnished by means of a polished steel jack chain, and the application of a little soft soap and hot water, or otherwise scratch-brushed. The beautiful frosted surfaces to be seen upon silver lockets, and other work of a similar nature, are all produced by means of the scratch-brush.

Burnishing is another mode of finishing silver work. It produces a polished surface, which reflects like a mirror, and gives the greatest lustre: it removes marks left by the polishing mixtures, and produces a darker surface than the other modes of finishing. The tools employed for this process are extremely variable, and well adapted to the different kinds of work to which they are applied; they are of two kinds, one being formed of hard stone, and the other of polished hardened steel; they vary with regard to shape, some being straight with rounded points, or with curved and blunted edges, others with large rounded surfaces, &c. Stone burnishers are made of blood-stone, which is mounted in a wooden handle with a brass ferrule, which firmly secures the stone to it, in which state it is used. Steel burnishers are likewise fixed in wooden handles, which enable them to be firmly grasped by the operator. Throughout the whole process of burnishing, the tool should be repeatedly moistened with a solution of soap and water; which causes it to glide more easily over the surface of the work, prevents it from becoming too much heated, and generally facilitates its action. In consequence of the great friction which the burnishing tool undergoes, it soon loses its bite, when it slips over the work as if it were greasy; its effectiveness must therefore be restored from time to time by rubbing it upon the leather which the workman has beside him for the purpose. It generally consists of a piece of buff leather, impregnated with a little crocus. In very small articles only steel burnishers are used, as they are finer in make, and by their greater variety of form, are exceedingly well adapted to all kinds of work; in this class of work, if any soap-suds should adhere to the article they may be removed by the application of a little tissue paper. Large pieces of work are rubbed with a piece of old linen, or washed in a warm solution of soap and water, rinsed, and dried in boxwood sawdust, which finally completes the process.

Silver work may be oxidized by any of the following processes:—

I.
Sal-ammoniac2 parts.
Sulphate of Copper 2 "
Saltpetre1 part.

Reduce the above ingredients to a fine powder, and dissolve it in a little acetic acid. If the article is to be entirely oxidized, it may be dipped for a short time into the boiling mixture; if only in parts, it may be applied with a camel-hair pencil, the article and the mixture both being warmed before using.

II.
Platinum1 part.
Hydrochloric acid 2 parts.
Nitric acid1 part.

Dissolve the platinum in the mixture of acid, evaporate to crystallization, and when cold, dissolve again in a little sulphuric ether. Apply the mixture with a camel-hair pencil to the parts required to be blackened.

III.
Saltpetre2 parts.
Common Salt1 part.
Spirits of Salts 1 "