and the different parts do not present the same composi tion. In a word, the mercury separates from its combination with the gold.

When using the amalgam, it is spread with the finger upon a flat, hard stone, called the gilding stone, and having dipped a scratch-brush of stout brass wire into quicking solution until it becomes completely white, it is then touched to the amalgam, a portion of which it carries away. The object, previously well cleansed, is scratchbrushed in every direction, and the brush is frequently dipped in a very dilute quicking solution in order to faci litate the regular spreading of the amalgam.

This operation requires great care to obtain a uniform coating upon the hollows and elevations.

When the back part of a piece does not require gilding, a portion beyond the edge should be gilded, in order that the naked copper shall cause no injury in the subsequent operations.

When the article is uniformly covered with the amalgam, it is heated over a charcoal furnace without draft, resting upon a cast-iron plate.* The entire attention of the operator is now required for watching the process. With his left hand covered with a thick glove of buckskin, he turns the piece in every direction upon the fire, and, as the mercury disappears, with his right hand he strikes the article in every direction with a brush, with long handle and bristles (Fig. 95), in order to equalize the gilding, and to work the remaining amalgam upon those parts which appear to require it.

* M. Darcet has devised a gilding forge which allows the workman to watch the operation from behind a glass frame, without the risk of inhaling the mercurial vapors. But such are routine and carelessness, that this apparatus has not become popular; and in most workshops a simple hood is used, and the workman remains constantly exposed to the fumes of mercury, the effects of which are most pernicious.

When all of the mercury has volatilized, the gilding has a dull greenish-yellow color, and the operator

Fig. 105.

then examines whether the coating of gold is continuous. Should a few uncovered places appear, a fresh quantity of amalgam is added, and the operation is repeated.

The next operation is scratch-brushing, which leaves the piece with a pale-green color, after which another heating is necessary for arriving at the desired shade. The re-heating should be sufficient for expelling any remaining mercury, and to produce a fine orange-yellow gilding.

Fig. 106.

We may now proceed to one of two distinct operations, according as we desire a bright or a dead surface. In the first case, we submit the object, with the aid of heat, to the ormolu process already described. In the second, the object is firmly fixed to an iron rod, with wire of the same metal (Fig. 106), and smeared with a hot paste for dead gilding, composed of nitrate of potassium (saltpetre), chloride of sodium (common salt), and the double sulphate of aluminium and potassium (potash alum). The whole is heated over a brisk charcoal fire, without draft, and moved about until the mixture becomes dry and begins to fuse, when the article is immediately plunged into a barrel, or cask, half filled with water, in the side of which a square opening has been made by two saw-cuts.

The covering of salts is immediately dissolved, and the dead lustre appears in all its beauty. This operation,

without being very difficult, requires a certain amount of practice, and is usually intrusted to a skilful workman.

The gilding must be strong to stand the dead lustre process, especially when (as is often the case) the first trial is not successful.

An object may possess the right kind of dead lustre, and still be covered with red lines left by the iron wire. These disappear by plunging the object into a not-toodiluted solution of nitric acid. Pure hydrochloric acid is preferable.

Fine gilders do not employ pure gold; that which they use is previously alloyed with a certain proportion of copper or silver. With the latter metal the gilding is green. Red gilding is either obtained with a dark ormolu or with the green-for-red, previously mentioned. (See the chapter on CHEMICAL PRODUCTS.)

Gilding with a partly Dead, partly Bright Lustre.

During the past twenty years, mixtures of bright gilding by the wet way, and dead gilding by fire, upon the same article, have been much in vogue.

In order to arrive at these results, operate as follows:Gild with the amalgam those parts which are intended to have a dead lustre, and heat, scratch-brush, and reheat to the orange-yellow color as directed. Then, with the current, give a sufficiently strong gold deposit to the whole, without regard to the parts already fire-gilded, scratch-brush all the surfaces carefully, and smear the electro-gilded portions, first with a thin mixture of water, glue, and Spanish-white, and afterwards with a thick paste of yellow clay. After drying, cover the fire-gilded portions with the paste for dead gilding, and proceed as has previously been explained. The Spanish-white, etc., are dissolved in a dilute solution of hydrochloric acid. The

size is intended to preserve from the heat the electrogilded portions, which are again wire-brushed with all the care necessary for not scratching the dead lustre. The operation is finished by burnishing.

This method, which is generally followed, is open to several objections, among which is the production of red spots on those places which have been heated too much, or where the coating of gold was not thick enough. It is easier and safer to proceed as follows:—

Gild with the amalgam, and in the manner above described, dead-lustre those portions which are to receive it, and preserve them entirely with "stopping-off" varnish. After thorough drying, cleanse the object by dipping in acids, in the usual manner, and gild in the electro-bath. The varnish will not be affected by these acids and solutions. When the desired shade is obtained, remove the varnish with benzole, which, without friction and without injury to either the shade or the velvety appearance of the dead lustre, rapidly dissolves it. Wash in a hot solution of cyanide of potassium, then in boiling water, and allow to dry in the air.

The varnish coating may also be removed by allowing the object to remain for a variable length of time in concentrated sulphuric acid of 66° Baumé, which has no action whatever upon the gilding. In this case, the washing with cyanide is unnecessary, and pure water is sufficient.

Gilding with a dead lustre, whatever be the process employed, is adapted only to those objects which will never be subjected to friction. Even contact with the fingers injures it.

A new freshness is imparted to old dead gildings by a washing in caustic lye, and then in a dilute solution of nitric, or sulphuric acid. This process is sufficient to re

heated, and then covered with the above mixture, which melts and is easily spread. For covering steel pinions, which generally form cylindrical projections upon the face of the wheels, a species of stylus of brass or copper is employed, having a wooden handle. (Fig. 101.) The metallic extremity of this tool is heated over an Fig. 101. alcohol lamp, and a small quantity of varnish is taken up with it. The composition soon melts, and, by turning the tool around the steel pinion, this becomes coated. Before fastening the pinion upon the cork, a small cavity is dug in the latter, in which the pinion rests. The remainder of the operation is conducted as with the other parts of the watch movements. Nevertheless, it is prudent to use a scratch-brush with long wires, as their flexibility prevents the removal of the composition. When, after gilding, the varnish is to be removed, the parts are plunged into warm oil, or into tepid benzine or turpentine, then into a very hot soap water, or alkaline solution, and lastly rinsed in fresh water. Scratch-brushing, and drying in warm sawdust of white wood, terminate the operation.

The pinions are cleaned out and polished by passing between them small pieces of very soft white wood, the friction of which is sufficient to restore to the steel its primitive lustre.

The gilding of those parts composed of copper and steel requires the greatest care, since the slightest rust will destroy their future usefulness. Should some gold have become deposited upon the steel, it should be removed by rubbing with a stick of wood and impalpable pumice dust, putty powder, or rouge.

10. Gilding. After the series of preparations above described, we come at last to the gilding, which may be