The base of most of the secret compo sitions for giving the antique appearance is vinegar with sal ammoniac. Skilful workmen use a solution of 2 ounces of that salt in an English quart of French vinegar. Another compound which gives good results is made with an ounce of sal ammoniac, and a quarter of an ounce of salt of sorrel (binoxalate of potash), dis solved in vinegar. One' eminent Parisian sculptor makes use of a mixture of half an ounce of sal ammoniac, half an ounce of salt, an ounce of spirits of hartshorn, and an English quart of vinegar. A good re sult will also be obtained by adding half en ounce of sal ammoniac, instead of the spirits of hartshorn. The piece of metal being well cleaned, is to be rubbed with one of these solutions, and then dried by friction with a fresh brush. If the hue be found too pale at the end of two or three days, the operation may be repeated. It is found to be more advantageows to operate in the sunshine than in the shade.
In bronzing plaster figures a cement may be used or not ; if used, the bronz ing will be more durable, the powders are mixed with strong pun water or isin glass, and laid on with a pencil. The sub-.
Jed may be covered with gold-size dilu ted with turpentine, and when nearly dry rubbed with a piece of soft leather.
Coins of copper and medals may be bronzed thus :—Dissolve in vinegar 2 parts of verdigris and 1 part sal ammoniac. Boil, skim, and dilute the solution with water until it ceases to let fall a white precipitate. The solution is then boiled and poured upon the objects to be bron zed, previously made perfectly clean and free from grease, the articles are then washed dried.
A deposit of brass or bronze may he thrown on objects by the electrotype pro cess, by employing a solution of 500 parts carbonate of potash, 20 parts chloride of copper, 40 parts sulphate zinc, 250 parts nitrate of ammonia.
For bronzing, a salt of tin is substitu ted for the zinc salt. By this solution, iron, cast iron, steel, lead, zinc, tin or their alloys are easily, coated with brass or bronze, by placing the article in contact with the negative pole of a Bunsen bat tery, and a plate of bronze or brass used as a positive pole.