a "stopping-off" varnish, which is dried in the air, or in a stove, or over a gentle fire until it no longer sticks to the fingers. The object is then ready to be put into the bath.

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Stopping-off" varnishes are generally solutions, in boiled linseed oil, or essence of turpentine, of certain resins, like copal, elemi, gallipot, etc.; and, as these varnishes are not sufficiently colored to distinguish the places where they have been laid on, they are mixed with a certain proportion of red-lead, or, preferably, chromeyellow (chromate of lead), which at the same time enhances their drying properties. The coloration of the varnish may also be produced with artificial ultramarine, or Prussian blue.

For a varnish that will resist the solvent power of the hot alkaline gilding liquid, Gore (Electro-Metallurgy, 182) recommends the following composition, viz:

A general receipt for a varnish by the same author is "best quick-drying copal varnish, with some peroxide of iron, or ultramarine mixed with it, for stopping-off' in hot cyanide solutions; or mixed with chromate of lead, if for use in cold liquids. It dries in about three or four hours." It is manifest that compositions for this purpose may be varied almost indefinitely, according to the convenience or personal preference of individual operators.

It is evident that the galvanic deposit will coat only those parts unprotected by the varnish. As far as practicable, the temperature of the bath should be low, and the current weak, for fear of having frayed lines along the

edges where the deposit touches the varnish, in consequence of the latter becoming softened, or from gas bubbles which are disengaged at the negative pole under the action of a strong electric current. When the deposit is completed, the varnish is removed with warm essence of turpentine, and afterwards with tepid alcohol; but it is preferable to use gasoline or benzole, which dissolve rapidly, and in the cold, nearly all resinous and fatty bodies, and which volatilize readily. The varnish may also be destroyed by a brief immersion in concentrated sulphuric acid when cold.

It often happens that several colors and metals are associated upon the same object, such as silvering, both bright and dead; gilding, yellow, green, red, white, or pink; and platinum, etc. The choice of the combinations which will appear the most pleasing is for the artist to determine. We have already stated in the chapter on "stopping-off" varnishes, which follows the gilding processes, that such varnishes were employed for avoiding the deposit of the precious metals where their presence would be useless.

CHAPTER XLI.

ORNAMENTING PLATED SURFACES.

OLD (ANTIQUE) SILVERING "OXIDIZED" SILVER-NIELLED

SILVERING-DEAD SILVER-SATIN FINISH.

Old (Antique) Silvering.—Articles silvered by the wet way may be given a patina, or antique appearance, by various methods, of which several are described in what follows.

This operation consists in imparting to silvered articles

certain tints resembling those of old artistic productions made of solid silver. With this object, the groundwork and hollow portions, which are not subject to friction, are covered with a blackish-red and earthy coating, while the parts in relief are left with a leaden, but brilliant lustre.

This operation is very simple. A thin magma of finely powdered plumbago (black lead) with spirits of turpentine. (to which a small proportion of red ochre is sometimes added, for imitating the coppery tinge of certain old silverware) is smeared all over the articles. After drying, a gentle rubbing with a soft brush removes the parts without adherence; and the reliefs are set off (discharged) by means of a rag dipped into alcohol. Old silver is of a pleasing appearance upon objects imitating antique cups, chandeliers, vases, statues, etc.

Old silver is easily removed, and the primitive brightness of the metal restored, by the use of a hot solution of caustic potassa, or cyanide of potassium. Benzole may also be employed.

In order to impart the old silver tinge to small articles, such as buttons, rings, etc., they are agitated in the above magma, and then "tumbled" with a large quantity of dry sawdust until the desired shade is obtained.

A great many operators, at the present day, produce the antique silvering by beginning with the oxidizing process about to be described, and setting off the reliefs by means of a hard brush and pumice-stone, or Spanishwhite. This last process is almost exclusively used for metallic mountings of books and albums.

Oxidized Silver.-This term is a misnomer, since the operation involves not an oxidation, but a combination with sulphur or chlorine. We have retained the word, simply because it has been consecrated by custom. !

It is well known that sulphur, soluble sulphides, and

hydrosulphuric acid (sulphuretted-hydrogen) blacken silver. This phenomenon may be noticed every day in the action upon this metal of the yolks of eggs (especially such as have lost their freshness), noxious gases, etc. It is also known (and the art of photography is based upon this phenomenon) that insoluble silver salts, and particularly the chloride of this metal, rapidly blacken under the influence of solar light.

It is thus easy to blacken silver, and consequently to "oxidize" it (using the word in its conventional sense), by treating it with one of the reagents above named. We may use vapors of sulphur, hydrosulphuric acid (free or combined), liver of sulphur or other polysulphides, hypochlorite of lime (bleaching-powder), or Javelle water. In the majority of cases, heat will be required to render the action of these substances more rapid.

The operation is generally conducted as follows:— Four or five one thousandths (that is to say, 4 or 5 parts to the thousand) of sulphide of ammonium, or, preferably, of pentasulphide of potassium (liver of sulphur) are added to ordinary water brought up to a temperature of about 150° to 175° F. As soon as the articles are dipped into this solution they become covered with an iridescent film of silver sulphide, which, after a few seconds more in the liquid, becomes blue-black. The article is then removed from the water, rinsed, scratch-brushed, and, if necessary, burnished.

As far as practicable, liquid should be used at once after its preparation, otherwise the prolonged heat will precipitate too much sulphur, and the deposit will be wanting in adherence to such an extent that it may be removed with the finger, leaving after it a red tinge resembling copper, although the material may be brass or German-silver. Moreover, the "oxidation" obtained in

the freshly prepared liquid is always brighter and blacker than that produced in old solutions, which is invariably dull and gray.

If the coating of silver be too thin, and the liquid too strong, the alkaline sulphide dissolves the silver, and the underlying metal (copper, etc.) is laid bare. In this case, we are obliged to cleanse and silver again, and to use a weaker blackening solution.

The silvering obtained with the paste previously described, exhibits the "oxidized" effect very well.

The same object is often oxidized and gilded by the following method: After the whole surface has been gilded certain portions are "stopped-off" by covering with varnish in order to silver the remainder. Should the process of silvering by paste be employed, the gilding should be very pale, because it is not preserved, and is deeply reddened by the sulphurous liquid. When this inconvenience occurs from a too concentrated liquid, it is partly remedied by rapidly washing the article in a tepid solution of cyanide of potassium.

The "oxidation" by sulphur, we have said, is blue-black. For a number of years another coloring, called deep black, has been substituted for it, which may be obtained directly upon cleansed copper. The manipulation is very simple, and is as follows: from 100 to 150 parts of hydrous carbonate of copper are dissolved in a sufficient quantity of aqua ammonia, and the cleansed articles of copper are rapidly plunged into this solution, cold or tepid, where they become instantaneously covered with a fine black deposit. This coat is so thin that burnished articles look as though varnished black.

Similar effects may also be obtained by depositing on the surface of the article, or on certain portions thereof, a film of metallic platinum. The platinum solution is pre