To oxidize silver any of the following may be used:
No. 1. Dissolve in 1 pint of water 1 cubic inch of sulphide of potassium, and apply to the silver.
No. 2. Slightly warm the silver article and apply hyposul-phuret of ammonium.
No. 3. Dissolve a pinch of chloride of platinum in a cupful of warm water and apply to the silver. The disadvantage of this recipe is that any platinum compound is very expensive.
No. 4. Place the silver in a small closed box with a piece of sulphide of potassium.
No. 5. Dissolve a pinch of barium sulphide in a cupful of warm water. Apply to the silver.
No. 6. Dissolve a pinch of ammonium sulphide in a cupful of warm water, and apply to the silver.
When using any of the above solutions to color silver, if the color is not dark enough add more of the chemical and if it is too dark weaken by adding water. To clean silver that is tarnished dip in a solution of 1/22 pounds of cyanide of potassium dissolved in 1 gallon of water.
Aluminum can be cleaned by immersing in a solution of caustic soda. To frost aluminum dissolve 2 ounces of caustic soda in 1 pint of water. A formula for blackening or oxidizing aluminum is as follows: chloride of zinc, 1 pound; sulphate of copper, 1 ounce; hot water, 2 quarts. Dip the articles in the solution. If the metal does not turn black fast enough, add a little more sulphate of copper.
As a last word of advice on the coloring of any metal, be sure that the chemicals are fresh, as almost all of the chemicals used in coloring deteriorate with age or exposure to the air.