CHAPTER XXVIII.

SILVERING.

BEFORE the discovery of the hydroplastic methods, there were in the arts two processes for silvering metals, and these two processes formed two separate industries. Artistic and useful objects of all kinds were manufactured from plated silver, i. e., copper plates coated with silver. On the other hand, articles entirely finished, as regards dimensions and shape, were plated with silver foil. There was, it is true, a method of silvering by the wet way; but the products were, and still are, so deficient in durability, that the process was known under the modest title of Whitening with Silver. We shall, nevertheless, examine this operation, which is still employed for whitening certain small wares, for which durability is of secondary importance, and which simply borrow the lustre and whiteness of silver; such are hooks and eyes, buttons, buckles for suspenders, articles for umbrellamakers, etc., which, sooner or later, return to the primitive color of their material-copper or brass.

CHAPTER XXIX.

of

PLATED SILVER.

PLATED silver is obtained by placing together a plate copper of the first quality, and one of silver, after introducing some powdered borax between them, then bringing them to a welding heat, and rolling out. The two metals are reduced and drawn out about equally by the pressure of the rolls, and long sheets or bands of silvered metal are thus obtained, from which a great variety of articles may be manufactured.

The inconveniences of this mode of operation are manifold; and we shall point out four principal ones: In the first place, a great quantity of material is lost, since we must cut out the objects from a sheet entirely silvered, and the waste retains a large proportion of the precious metal; in the second place, the cut sections are denuded of silver, and these must be hidden either by silvering by some other method, or by some other artifice.

The third inconvenience is the absolute necessity of employing pure copper, which is more costly, less sonorous, and not so tough as the alloys of this metal.

The fourth defect, which is a capital one, arises from the fact that the coating varies in thickness according to the shape of the object manufactured from the plate. It is evident that, in the stamped, beaten-out, or embossed parts, the bottom of a vase for instance, the silver has increased in surface, and therefore that its thickness is less than that of the flat surfaces. Moreover, these raised

surfaces are the more exposed to friction, and it is just there that the coating of silver is the thinnest. We shall see further on that the conditions are reversed with electrosilvering, and that the parts in relief receive a more abundant deposit of silver, which is a great desideratum.

The best plated silver has one-tenth of silver, and is manufactured by uniting to an ingot of pure copper weighing 9 pounds, another ingot of pure silver weighing 1 pound. The two are rolled together until the desired thickness is obtained. It is even possible to produce a bad plated silver, with one-tenth of the precious metal; for, should we roll the two metals until the foil of silvered copper becomes, say of an inch thick, the thickness of the silver will be only of an inch. Articles manufactured with such foil will possess only the strength imparted to them by the lead, mastic, or cement with which they are filled.

ठ

1

The silver of the plated metal will appear bright if the rolls are well polished, and dull if the rolls are unpolished.

If the rolls are engraved on their circumferences, it is obvious that the design will be reproduced in relief on the rolled plate.

A sheet of copper, rolled between two sheets of silver, will, of course, be plated on both sides.

To unite the several parts that compose an object of plated silver, the only practicable solder, which does not injure the silvering, is tin solder; and when the manufactured objects are required to resist a certain temperature, chafing dishes for example, screws or rivets are employed to unite the parts.

When the silver of the plated article became worn off in certain places, there was no satisfactory method of remedying it until the invention of the hydroplastic processes.

CHAPTER XXX.

LEAF-SILVERING.

THIS method, as distinguished from the use of plated silver, is only practised upon objects already manufactured, and with their finished shape; furthermore, it is adapted to all kinds of copper, bronze, German-silver, or brass. It is therefore, in certain respects, superior to plated silver; but it is very difficult of execution, and the silver is less adherent to the metal beneath.

The operation is conducted as follows:

After annealing the articles, they are thrown, still hot, into a bath of sulphuric acid, containing a small proportion of hydrochloric and nitric acids. They present then a dull and dead surface, owing to a multitude of small depressions, which serve as so many points of attachment for the silver-leaf which is subsequently applied.

The objects, thus prepared, are firmly attached to an iron rod, which is held in a vise. Their temperature is raised to about 300° Fah., by pieces of incandescent charcoal laid on the part operated upon, and removed so as to open the pores of the metal, which, on subsequently cooling and contracting, so to speak, imprisons the molecules of the silver applied. The silver-leaves are taken from the book with small tweezers, and are cut to the proper dimensions upon a cushion, with an ivory or steel knife. After each fragment is deposited upon the object, it is made to adhere by gentle pressure with a soft pad, and the operation is finished by friction with a burnisher

of polished steel. The parts of silver foil which do not adhere are removed with a soft brush. It is possible in this manner to superpose a large number of leaves upon each other on the same object, but their adherence will be in an inverse ratio to their number.

Gold-beaters prepare silver leaf either bright, or dead. The latter is made to adhere only by the pressure of the pad, and not by the burnisher. This dead lustre does not, however, equal in fineness that obtained by the battery; it is true, however, that it resists handling, and the action of deleterious gases in the atmosphere, better than the latter.

Articles thus silvered are burnished only after the article is completely covered; round or cylindrical objects are burnished upon the lathe, and other forms by hand.

A practised eye will readily ascertain whether an object has been silvered with leaf, as the burnisher nearly always leaves upon the surface a series of zones or striæ.

This method of leaf-silvering, at the present time, is employed only for very large objects; or for ecclesiastical ornaments, such as high chandeliers, crosses, holy-water basins, etc.

Roseleur states that at one time the use of leaf silver for silvering spoons and forks was tried in France, but that the attempt was soon abandoned. The method of operation, he describes as follows: The articles were first covered with a film of matt silver by immersion, heated, and then covered with leaf silver. The adherence of the latter was obtained by the pressure of an iron scratchbrush striking vertically, and forcing the silver leaf, as it were, into the pores of the subjacent metal. Burnishing by the usual method finished the operation. It was therefore impossible by this method to obtain a dead surface.