The dark colors in silvered cast zinc articles are obtained by coating same with a solution of liver of sulphur, and also by rubbing with graphite.
In making mirrors, mercury or quicksilver is poured over tin foil and the glass (absolutely clean) carefully slid upon it so as to exclude the air, when weights are placed upon it and allowed to remain several hours. The mercury and tin foil combine and adhere to the glass.
(2) The glass is first silvered by means of tartaric acid and ammoniacal nitrate of silver, and then exposed to the action of a weak solution of double cyanide of mercury and potassium. When the mercurial solution has spread uniformly over the surface, fine zinc dust is powdered over it, which promptly reduces the quicksilver, and permits it to form a white and brilliant amalgam, adhering strongly to the glass, and which is free from the yellowish tint of ordinary silvered glass, and not easily affected by sulphurous emanations.
To determine whether silvering on an article is light or heavy, clean same with either ether or alcohol and apply to it a drop of 1 5-10 per cent. solution of bi-sulphate of soda. Allow the drop to act for ten minutes and rinse it off with water. If the article is deeply silvered a full round steel-gray spot is produced. Other white metals, barring amalgamated copper, do not show this, but, instead, a ring at the edge of the drop.
Take nitrate silver 2 drachms, distilled water 4 1/2 ounces. Dissolve, and add sal-ammoniac, hyposulphite soda and precipitated chalk each 4 drachms. Mis.
All surfaces to be plated must be thoroughly cleansed and polished before applying the solution.
A silver ink may be made by rubbing up silver bronze with honey and water.
To determine whether an article is silver or silvered apply the following test: viz., a fluid consisting of 16 parts chromic acid and 32 parts of distilled water. The surface of the article to be tested is to be filed, and the filed place put on the touch-stone and the test water applied. If genuine silver, the touchstone becomes blood red. The deeper the coloration, the finer the quality of the silver. If the article be not genuine silver, but silvered, German silver, tin compositions, etc., the touch is not decomposed by the test water, but cast out in its original color, or, perhaps, in extreme cases, with a dull gray tint.
This alloy is very white and fine-grained, and has great tenacity. It is used in place of brass or gun metal where a superior polish is required and is composed of copper and nickel, to which, according to the different purposes for which it is desired, zinc, lead and tin are added.
Silver sulphate is made by the action of hot, concentrated sulphuric acid on silver.
Silver sulphide is made by the fusion of silver with sulphur.
Similor is a copper-zinc alloy composed of:
89 44-100 parts Copper, 9 93-100 parts Zinc, 62-100 parts Tin.