Читать книгу Henley's Formulas, Recipes and Processes (Applied Chemistry) - Various - Страница 602
How To Bronze Metals.
Оглавление—Prepare a solution of 1 1/2 ounces of sodium hyposulphite in 1 pint of water and add to the same a solution of 1 1/2 ounces of lead acetate dissolved in 1 pint of water.
If, instead of lead acetate, an equal weight of sulphuric acid (1 1/2 ounces) is added to the sodium hyposulphite and the process carried on as before, the brass becomes coated with a very beautiful red, which changes to green, and finally a splendid brown with a green and red iridescence. This last is a very durable coating and may be especially recommended. It is very difficult to obtain exact shades by this process without some experience. The thorough cleansing of all articles from grease by boiling in potash is absolutely necessary to success. By substituting other metal salts for the lead acetate many changes in tints and quality of the coatings can also be effected.
When this mixture is heated to a temperature a little below the boiling point it precipitates sulphide of lead in a state of fine division. If some metal is present some of the lead is precipitated on the surface and, according to the thickness of the layer, different colors are produced. To produce an even color the articles must be evenly heated. By immersion of brass articles for 5 minutes the same may be coated with colors varying from gold to copper red, then to carmine, dark red, and from light blue to blue white, and at last a reddish white, depending on the time the metal remains in the solution and the temperature used. Iron objects treated in this solution take a steel-blue color, zinc a brown color. In the case of copper objects a golden yellow cannot be obtained.
