move the greasy spots, dust, and smoke, but, evidently, will not remedy scratches. In the latter case, the objects must be scratch-brushed, and then heated with the deadlustre composition.

CHAPTER XXVI.

DEAD-GILDING ZINC.

THERE is, at the present time, no artistic bronze, whatever be its finish, and its elegance of shape, which may not be reproduced in zinc (dignified with the name of Bronze composition) with an accuracy which often deceives the most practised eye. Most of our stores are filled with clocks, chandeliers, cups, and other articles de luxe, made of zinc only. Many such articles are simply bronzed to imitate similar objects of real copper, brass, or bronze; but others rival in their gilding the finest fire-gilt products, with dead lustre, scratch-brushed, or burnished.

Gilded zinc, especially with dead lustre, is, at the present day, manufactured in France on such a large scale, that it will be serviceable to devote an entire chapter to the manner of executing it.

The first operation consists in stopping with tin solder all the holes and the small fissures which may exist in the object of zinc, and, at the same time removing, with appropriate tools, the seams, burrs, rough spots, etc.

Afterwards, the piece is cleansed by passing it, for a few seconds only, through a boiling solution of 100 parts of water and 5 or 6 parts of caustic potassa or soda. Too long a sojourn in this caustic lye will destroy the

After

It is

polish of the zinc, as the metal begins to dissolve. this cleansing, the object is rinsed in fresh water. then steeped for half a minute in a pickle composed of 10 parts of sulphuric acid, and 100 parts of water, and lastly rinsed in cold, or preferably, boiling water.

Thus prepared, the object is immersed either in a cold or warm, electro-bath for coppering or brassing, for a few moments, or until it has been covered with a thin metallic film, which is deposited very uniformly if the object has on it no tin solder, and has been perfectly cleansed.

On the contrary, the deposit is black and dull on those parts which have been soldered, or imperfectly cleansed. In the latter case, the article is thoroughly scratch-brushed, and dipped again into the electro-bath for a half hour or an hour, until the deposit is sufficiently thick. Most gilders use a warm bath for the preliminary coating, scratchbrush, and complete the deposit in a cold bath.

If a bright gilding be desired, the article may be rinsed in fresh water, and then conveyed to an electro-gilding bath.

On the other hand, if we desire a dead-lustre gilding, equal in appearance to the best fire-gilding, we proceed by either of the following methods:

First Method.- With Silver.

An electro-silvering bath is prepared by dissolving in 1000 parts of water 15 parts of fused nitrate of silver, and adding 25 parts of pure cyanide of potassium, which, at first, produces an abundant precipitate, which soon dissolves. The filtered liquid is the silver bath, into which the zinc article, previously coated with copper or brass, is immersed. Under the influence of a properly adjusted electric current, the silver deposited is of a very

handsome frosted (dead-lustre) appearance, and perfectly white. The object is then rapidly and thoroughly rinsed, and immersed in an electro-gilding bath, of which we shall give the formula.

The dead-gilding obtained by this process is very fine and satiny, but is soon altered and darkened by the sulphuretted-hydrogen in the atmosphere (and from which coal gas is not entirely free), which sulphurizes the silver through the thin film of gold.

This process is seldom employed at the present day, and the following one is preferred, and rightly so, since it is more durable and more economical :

Second Method.-By Galvanoplastic Processes.

Add to a suitable quantity of water, one-tenth of its volume of sulphuric acid, and dissolve in this acid liquid, as much sulphate of copper (blue-vitriol) as it will take up at the ordinary temperature. This solution will then mark from 20° to 24° Baumé, and should be diluted with enough water to reduce its density to 16° or 18°.

This electro-bath is generally contained in large vessels of stoneware, slate, wood, or gutta-percha; and porous cells are immersed in it, which are filled with a weak solution of sulphuric acid and of amalgamating salts. Plates, or cylinders, of zinc are placed in these cells, and are connected with one, or several brass rods, which rest upon the sides of the trough, and support the articles which are to be treated. (Fig. 107.) The articles of zinc, previously coated with copper or brass, are then suspended to the rods, and remain in the solution of sulphate of copper until they have acquired a satisfactory dead lustre.

It is prudent, a few seconds after the articles have been immersed in the bath, to take them out, and examine

them carefully. Indeed, should the previous coating of copper or brass be insufficient to resist the corroding action of the acid solution of sulphate of copper, there is produced a muddy and dark deposit,

Fig. 107.

which is easily removed with the finger. And should this occur, the objects must be scratch-brushed and placed again in the former alkaline coppering or brassing baths, in order to increase the deposit which should protect the zinc in the galvanoplastic bath.

The beginner, before undertaking this operation, will do well to consult, and become conversant with, the second. part of this work which treats of the galvanoplastic art proper.

When the galvanoplastic dead-lustre has been successfully obtained, the deposit is perfectly regular, and of a pink shade. When, on the contrary, it is irregular, marbled, crystalline, of a vinous color, and dull or earthy in appearance, these defects are due to the following causes: either the bath is in a bad state of conductibility, or of

saturation; or the surface of the zinc is too considerable in proportion to that of the objects; or, lastly, the previous electro-deposits of copper or brass were insufficient or inferior in quality. The remedy for either of these inconveniences is easily applied, and simply requires a little care and attention.

The galvanoplastic dead-lustre being once obtained in a satisfactory manner, two preliminary operations are needed to insure the success of the gilding.

They consist in rapidly passing the object (with dead lustre), after rinsing, through a solution composed of:1000 parts.

Water

Nitrate of mercury
Sulphuric acid

1 part.

2 parts.

Then, after rinsing, plunging it into another solution composed of:

After coming out of this bath, the object has acquired a whitish tinge, and is again rinsed in fresh water, before being placed in the following gilding bath:

The mode of preparation of this bath is given at the beginning of Chapter XXI.

This bath should be nearly boiling, and worked with a strong galvanic current. The anode is a platinum wire, which, being more or less immersed in the liquid, allows of the regulation of the current according to the volume, weight, and surface of the object to be gilded.