The articles to be gilded must be constantly agitated in the bath, and are supported by a hook or in a stoneware ladle perforated with holes, or in baskets of brass gauze, according to their shape or size. (See Figs. 1 to 9 of this work.)

Important as are the minute precautions here indicated, they are far from being observed by gilders well conversant with this kind of work. For the preparation of their baths, they are satisfied with dissolving the pyrophosphate in ordinary water, and adding at the same time the prussic acid. Their gold is dissolved as above described, and its solution, without previous filtration, is added to that (more or less hot) of the pyrophosphate.

Gilders by the immersion process usually employ three baths, disposed in close proximity to each other, and heated upon the same furnace, either by charcoal or gas.*

*The gas furnace, which is the most convenient and economical one (Fig. 91), is made of a sheet-iron box provided on top with three

Fig. 91.

Inside, and

holes intended to receive the bottoms of three kettles. under each kettle, is a Bunsen burner composed of five or six jets burning with a blue flame. These jets are often replaced by a species

The first bath is one that has been nearly deprived of gold by a previous operation, but is used for removing any acid which may possibly remain upon the articles. to be gilded. The second bath still contains some gold, but not enough to give a sufficiently rich and dark gilding. By commencing the gilding in this, the gold remaining in it is utilized, while at the same time the strength of the third bath, in which the gilding is finished, is advantageously husbanded.

It need hardly be said, that the fresh bath of to-day becomes the second of to-morrow, and so forth.

This method of operating allows of much more gilding with a given quantity of gold, than with one bath alone. It explains, likewise, why it is that well-organized works having a number of baths at work at one time are able to produce a cheaper and finer gilding that their confrères whose arrangements are not so practical.

The gilding is done in a few seconds, and the finishing operations consist in rinsing in fresh water, drying in dry and warm sawdust, and, if necessary, burnishing.

A good sawdust should be free from resinous and other impurities, and should be that from white woods, of which that from fir, poplar, and linden is especially to be recommended. That of oak and walnut blackens the gilding; and that of boxwood, although often employed, is not sufficiently absorbent.

After drying very small articles in sawdust, the latter

of rose-jet burner, inside of which the mixture of gas and air takes place. This apparatus bas two separate stopcocks, one connected with a small central jet, and the other with the rose burner. When both cocks are open, the gas is lighted at all the apertures, and the baths are rapidly heated up to the point of ebullition. The cock of the rose burner is then turned off, and the heat of the central jet is sufficient to keep up the proper temperature.

し

substance is removed by sieves of various numbers, or by winnowing.

Coloring Process.

It happens sometimes, that, through neglect of some of the precautions above indicated, the gilding is dull and irregular in tone. We must then have recourse to coloring, which is conducted as follows:

Fuse together in their water of crystallization, and at about 212° Fahr., equal parts of— Sulphate of iron (copperas).

Sulphate of zinc (white vitriol).

Sulphate of aluminium and potassium (potash alum). Nitrate of potassium (saltpetre).

Smear the imperfectly gilded articles with the mixture, so that all parts are well covered, and place them in the centre of a cylindrical furnace (Fig. 92) in which the

Fig. 92.

fuel (charcoal) is disposed in the annular space between the furnace walls and the cylindrical and vertical grate.

The central portion, into which the heat radiates, receives the objects. Fig. 93 represents a vertical section, and Fig. 94, a plan, of this apparatus.

The salts begin to dry, then to fuse, and the mass acquires the dull appearance of yellowish clay.

When the moistened finger is presented to one of the pieces and a slight hissing sound is heard, it is evidence that they have been sufficiently heated, and all the articles are then removed, and quickly immersed in a very diluted solution of sulphuric acid, where the external coating of salts which covers the gilding at once dissolves, leaving this of a warm and uniform shade of color.

This process will evidently only answer the purpose when all parts of the copper articles have been entirely covered with gold by the first operation. If they are not, the ungilt portions will show themselves by a red coloration, and the articles must then be "stripped" of their gold, cleansed, and gilded anew. We shall shortly indicate the processes by which these results are arrived at without injury to the copper or its alloys.

At the present time, the majority of gilders by immersion, gild also with the battery; and, when the first gild

ing is imperfect, instead of coloring by the process just described, they place the articles for a few moments into the electro-bath, which is preferably worked hot, and the composition of which will be given further on.

CHAPTER XIV.

ORMOLU-COLORED GOLDS-GREEN AND WHITE GILDINGGILDING SILVER BY SIMPLE IMMERSION.

Simple-Immersion Gilding (continued).

WE have said that, generally, immersion gilding is especially resorted to for false jewelry. There is, however, an easy method of obtaining by this process results rivalling those obtainable by the battery, and which consists in gilding several times, by dipping, those objects which require a good plating. The secret is, that before each immersion, the article is "quicked," i. e., passed through the solution of nitrate of mercury. By this operation, a coating of mercury is deposited at each operation, and dissolving in the bath of pyrophosphate, is each time replaced by a fresh coating of gold.

This method is constantly applied to the plating of large pieces, such as clocks, chandeliers, ornamental bronzes, etc., which are usually gilded by the battery. Executed by this method immersion gilding, as compared with electro-gilding, is superior in richness of tone, brilliancy, lustre, and especially in having no tendency to scale off, as the deposit obtained by this system consists of pure gold only, whereas, by the galvanic process, a subsalt of this metal is often deposited.