Oxidised Silver

(a) This is not an oxidation, but a combination with sulphur or chlorine. Sulphur, soluble sulphides, and hydrosulphuric acid blacken silver, and insoluble silver salts, and particularly silver chloride, rapidly blackens by solar light. Add four or five thousandths of ammonia hydro-sulphate, or of potassium quintisulphide, to ordinary water at a temperature of 160°-180° F. When the articles are dipped into this solution, an iridescent coating of silver sulphide covers them, which after a few seconds more in the liquid turns blue-black. Remove, rinse, scratch-brush and burnish when desired. Use the solution when freshly prepared, or the prolonged heat will precipitate too much sulphur, and the deposit will be wanting in adherence; besides the oxidation obtained in freshly-prepared liquors is always brighter and blacker than that produced in old solutions, which is dull and grey. If the coat of silver is too thin, and the liquor too strong, the alkaline sulphide dissolves the silver, and the underlying metal appears.

In this case cleanse and silver again, and use a weaker blackening solution.

(6) Oxidised parts and gilding may be put upon the same article by the following method: After the whole surface has been gilt, certain portions are covered with the resist varnish, silver the remainder. Should the process of silvering by paste and cold rubbing be employed,- the gilding should be very pale, because it is not preserved, and is deeply reddened by the sulphur liquor. When this inconvenience occurs from a too concentrated liquor, it is partly remedied by rapidly washing the article in a tepid solution of potassium cyanide.

(c) Deep black is thus obtained upon cleansed copper: - Dissolve 3-4 oz. blue ashes (copper hydrocarbonate) in a sufficient quantity of aqua ammonia, place the cleansed copper in this solution, cold or tepid; it will be instantaneously covered with a fine black deposit. This coat is so thin that burnished articles look like varnished black.

(d) Oxidise silver-plated articles by dissolving copper sulphate, 2 dwt., potash nitrate, 1 dwt., and ammonia muriate, 2 dwt., in a little acetic acid. Apply with a camel-hair pencil; but warm the article first, and expose it to the fumes of sulphur in a closed box; the parts not to be coloured must be coated with wax.

Silvering Brass

(a) Take 1/4 lb. potassium cyanide and 1/2 oz. silver nitrate; dissolve all the cyanide in 16 oz. distilled or boiled water, and the silver in a similar quantity in another vessel. Into the vessel containing the silver, throw a spoonful of common salt; stir this up well with a clean piece of wood and let it settle; dissolve some salt in water, and after the silver solution is settled mix a few drops of the salt water in it. If there is any cloudiness formed, it proves that all the silver is not thrown down; more salt must be added, and then stir and allow to settle. If the addition of salt water has no effect, the water may be decanted off, carefully preserving the white deposit. Now pour some boiling water on this deposit; let it settle, and pour off as before. Do this at least three times; pour off as dry as possible, and add about 1 pint clean water, and then by 1/2 oz. at a time, the cyanide solution, till all the white precipitate is dissolved; add enough water to make 1/2 gal. Stir well after each addition of cyanide solution.

If on dipping the article, which must be well cleaned with brick-dust and water, into this solution the silver deposits immediately and in a dark powder, it must be weakened by adding more water; if it coats slowly, more white precipitate must be prepared, washed, and added to it. This must also be done when the solution is getting short of silver. It works best at about 60°-70° F.; a dry, warm room suits the operation. Brass and copper only can be silvered; other metals require a battery. This method gives a beautiful result when the work is polished and burnished.

(6) Clean the articles thoroughly, and then immerse them for a few seconds in a solution of silver cyanide, which will plate them without any further trouble.

(c) A silvering solution, which will cover brass, German silver, and copper with a thin but substantial film of silver, may be made by adding to a strong solution of silver nitrate sufficient of a solution of potassium cyanide to re-dissolve the precipitate at first thrown down. Mix in with this sufficient Spanish whiting or precipitated chalk to make a thin paste. This solution, to obtain its best effect, should be slightly warmed before application, and the articles to be silvered should' be clean and free from grease. By scattering or rubbing zinc filings over the surface to be silvered, especially if it be of copper, a much more beautiful effect is produced, the filings being washed off after the silver coating is obtained.

(d) To coat copper or brass objects with silver, without difficulty or loss of time, mix 3 parts silver chloride with 20 of powdered cream of tartar and 15 of powdered common salt. Moisten a suitable quantity of the mixture with water, and rub it with a piece of blotting paper upon the metallic object, which must be thoroughly clean. The latter is afterwards rubbed with a piece of cotton upon which precipitated chalk is dusted, then washed with water, and polished with a dry cloth.

Silvering Britannia Metal, Pewter, And All Combinations Of Lead And Tin

These are best placed in a solution containing a good deal of free cyanide, and the deposit should be rapid at first. The surface of the anode should be about three times that required for German silver, and the battery power strong, but not too intense. It is better not to disturb these articles in the solution at the beginning of the deposit. Afterwards they may be shifted for obtaining a uniform coat. If the articles, when they have been a short time in the plating bath, present an unequal surface, remove them, and brush over again as before; then, after well rinsing, return quickly to the bath and allow them, if possible, to remain without further disturbance.