Pure silver is quite soft, and is, therefore, generally alloyed with copper to harden it.
Silversmiths' work, after having been filed is generally rubbed, firstly, with a lump of pumice-stone and water; secondly, with a slip of water-of-Ayr stone and water; thirdly, a revolving brush with rottenstone and oil; fourthly, an old black worsted stocking with oil and rottenstone, and fifthly, it is finished with the hand alone, the deep black lustre being given with rouge of great fineness. The corners and edges are often burnished with a steel burnisher, which is lubricated with soap aud water if at all.
In this case and in all others of polishing with the naked hand, it is generally found that women succeed better than men, and that some lew, from the peculiar texture and condition of the skin, greatly excel in the art of polishing. The skin should be soft and very slightly moist, as the polishing powder then attaches itself conveniently, and there is just sufficient adhesion between the hand and work to make the operation proceed rapidly. A dry hand becomes hard and horny, and is liable to scratch the work, and excess of moisture is also objectionable, as the hand is then too slippery.
The plated reflectors for light-houses are cleaned with rouge, which is dusted on from a muslin bag, and rubbed over them with a clean dry wash-leather.
A thin film of oxide will nevertheless occasionally form on the surface of the reflector, and this is removed with a piece of leather, with rouge moistened with spirits of wine, which dissolves the oxide, after which the dry rubber is applied as above.
This is not an oxidization, but a combination with sulphur or chlorine. Sulphur, soluble sulphides, and hydrosulphuric acid blacken silver, and insoluble silver salts, and particularly the chloride of silver, rapidly blackens by solar light. Add four or five thousandths of hydrosul-phate of ammonia, or of quintisulphide of potassium, to ordinary water at a temperature of 160° to 180° Fahr. 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 oxidization 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 appear In this case cleanse and silver again, and use a weaker blackening solution. Oxidized 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 cyanide of potassium.
A very beautiful effect is produced upon the surface of silver articles, technically termed oxidizing, which gives the surface an appearance of polished steel. This can be easily effected by taking a little chloride of platinum, heating the solution and applying it to the silver where an oxidized surface is required, and allowing the solution to dry upon the silver. The darkness of the color produced varies according to the strength of the platinum solution from a light steel gray to nearly black. The effect of this process, when combined with what is termed dead work, is very pretty, and may be easily applied to medals, and similar objects.
The high appreciation in which ornaments in oxidized silver are now held, renders a notice of the following processes interesting. There are two distinct shades in use - one produced by a chloride and which has a brownish tint, and the other produced by sulphur, which has a bluish- black tint. To produce the former it is necessary to wash the article with a solution of sal ammoniac; a much more beautiful tint may, however, be obtained by employing a solution composed of equal parts of sulphate of copper and sal ammoniac in vinegar. The fine black tint may be produced by a slightly warm solution of sulphuret of potassium or sodium.
The chloride of platinum mentioned above is easily prepared as follows: Take 1 part nitric acid and 2 parts hydrochloric (muriatic) acid; mix together and add a little platinum; keep the whole at or near a boiling heat,; the metal is soon dissolved, forming the solution required.