with a brush covered with plumbago; and as upon this operation depends the regularity of the deposit, care must be taken to render the surfaces completely black and lustrous, without gray or whitish spots.

A process of black-leading moulds by the wet way, which gives very superior results, has been devised by Mr. S. P. Knight. He uses an emulsion of finest plumbago and water, and forces the same by means of a pump and a travelling fine-rose nozzle over the surface of the moulds, which are placed upon suitable supports. The surplus liquid is returned and used over again. The process is specially intended for electrotypers' use.

When the model is very indented or undercut, it becomes difficult to employ plumbago, and, in such case, the entire mould, or at least the cavities, are metallized by the wet way, about to be described.

It is generally believed that soft brushes should be employed for spreading the plumbago upon moulds. This is a mistake which prevents many from succeeding; Roseleur uses watchmakers', and even blacking brushes, with which he obtains sufficient friction to cause the adherence of the plumbago without injury to the mould. Artists' modelling wax alone requires soft brushes.

The metallization of stearined objects succeeds well with alabaster, plaster of Paris, wood, etc. For the latter, however, Roseleur prefers a protracted steeping in fatty oil, or simply in linseed oil. The object must be rubbed dry before the plumbago is applied.

When the substances to be metallized are not porous, they are covered with a thin coating of varnish, which, when nearly dry, receives the plumbago. This method applies to glass, porcelain, stoneware, horn, and ivory.

It is by analogous processes, that M. Oudry has succeeded in producing, on the commercial scale, those great

galvanoplastic works which contribute so largely to the decoration of the streets, public gardens, and squares of Paris. Such are the monumental fountains and candelabra for gas lights, which this inquiring and indefatigable worker has succeeded in coating with a copper deposit, sufficiently uniform to respect the beauty of the ornaments, and durable enough to withstand shocks and friction, and the action of the atmosphere, and capable of assuming the appearance of various bronzes. These products are generally made of cast-iron. Many trials had been made to coat them with a sufficient thickness of copper; but all these attempts, which were conducted in the same manner, that is to say, a previous cleansing of the cast-iron in acid pickles, a first coating of copper in the bath of double salts, and then the finishing coat in sulphate of copper, proved to be failures on account of the imperfections of the material operated upon. Cast-iron is always porous, full of cavities, and exhibits on its surfaces particles of sand, carbon, and other impurities; therefore the deposit of copper presented similar imperfections, and was not continuous. The result was that moisture soon penetrated between the two metals, the iron was oxidized, and the copper coating detached.

Avoiding the errors of his predecessors, M. Oudry, instead of cleansing the cast-iron, covers it with a thin layer of fat varnish, very plastic and resistant, and, at the same time, sufficiently elastic to adapt itself to the expan sion and contraction of the metal without cracking. When this varnish is nearly dry, it is covered with plumbago, and the object is immersed in the depositing vat. Such is the process by which are coppered, and then bronzed, a multitude of objects of wrought and cast-iron intended to withstand the action of the atmosphere. M. Oudry thus manufactures a great variety of garden benches,

fountains, vases, statues, railings, etc., and could cover the entire hull of a ship with a continuous copper sheathing, if he had a depositing vat large enough to contain it.

Metallization of Ceramic Wares.

For ceramic wares, other processes are employed, which give more rapid results.

After having varnished the portions of the piece to be coppered, they are covered with very finely laminated sheet lead, which readily adapts itself to the contours of the object; then a brass conducting wire is connected with the lead, and the article is suspended in the copper bath, where the copper is immediately deposited upon the metallic parts. By similar methods, glass flasks and retorts, tubes, dishes, and other culinary vessels of glass, stoneware, earthenware, or porcelain, are coated with a continuous coating of copper. Unfortunately it is found that owing to the unequal expansion and contraction of the article and of the copper deposit, the adherence between the two surfaces is soon destroyed.

Nevertheless, the decorative arts have made good use of this species of deposit, and we have crystal vases entirely covered with copper, upon which have been successively deposited other layers of gold and silver. The chaser may then penetrate with his tool to different depths, and uncover one after the other, and at determined places, first the layer of silver, next that of copper, and at last the crystal itself. The vase will appear as if set in a network of various colors. A goblet, a paper weight, and any analogous article may, of course, be treated in the

same manner.

M. Chablin, a skilful electrician and artist, ornaments porcelain, ceramic, and crystal wares on a large scale, by

galvanoplastic processes. His method of metallization is quite different from those described, inasmuch as he simply uses as a conducting metal the coating of gold which is applied upon porcelain by the old and wellknown processes. The fineness of the details can scarcely be surpassed, and the durability and firmness of the deposit are remarkable. Let us suppose that a plate of porcelain is to receive in its centre an ornament or ini tials in metals and in relief: the device in leaf gold is first attached to the surface with the pencil, and fixed in the usual manner by heating the plate in a muffle. The metallic film thus obtained is made to serve as the basis of a galvanic deposit. It is connected with a very thin conducting wire, and the whole immersed in a galvanoplastic bath of copper, silver, or gold, where the deposit takes place in the same manner as upon an ordinary metallic or metallized surface, and the adherence is as perfect as that of the film of gold upon the porcelain. The deposit is afterwards polished, chased, or ornamented on the lathe. Nothing can exceed the beauty of this species of ornamentation, and the numerous specimens seen in our jewelry stores often puzzle the beholder to understand how they have been produced.

Metallic Powders.

We have said that when a metal is immersed in the bath of sulphate of copper, the entire surface is immediately covered in the case of a surface metallized with plum bago; on the other hand, the deposit starts from the points of contact of the conducting wire, and radiates from these slowly in all directions. It follows, therefore, that while the metal is an excellent conductor of electricity, plum bago is relatively a poor one.

It has, therefore, been attempted to replace plumbago

by metals in the state of exceedingly fine powders; and bronze powders, shell-gold, silver reduced by copper or hydrogen, antimony, and bismuth, in impalpable powder, have been successively tried without good results, either from a want of adherence, or from the solvent action upon them of the copper bath. Some operators, however, continue to use a mixture of bronze powder and plumbago, and claim to be satisfied with it; but Roseleur prefers the gilt or silvered plumbago, prepared in the manner already described. These are doubtless excellently adapted for galvanoplastic work on the small scale, but for large operations, and for electrotyping, will be altogether too expensive. (See our remarks on the processes of Knight and Adams).

Metallization by the Wet Way.

Although the results obtained by the mechanical application of various metals in impalpable powder are not entirely satisfactory, such is not the case with the metallization produced by the reduction, upon the object itself, of certain metallic salts. Silver, gold, and platinum, thus reduced from their solutions, have an excellent conducting power, for the reasons, probably, that they are not acted upon chemically by the bath, and because they form a layer more nearly continuous.

Silver is generally preferred, and for this purpose a solution of the nitrate is made, and this solution is applied with a pencil upon the object to be operated on, and allowed to dry, and the operation repeated two or three times. Lastly, the object is exposed to the action of sunlight, or of a current of hydrogen. A convenient plan is to subject it, in a hermetically-sealed box, to the vapors of a concentrated solution of phosphorus in bisulphide of carbon contained in a porcelain evaporating dish.