Reduce the salts to powder, and place it in a black-lead crucible along with the acid, boil up, and then dip the articles into the mixture for a short time, or otherwise apply it to the parts required to be oxidized.
These mixtures will give the various tints of oxidation to silver work if properly treated; but if other tints be desired, the following chemical substances may be employed according to taste:—For slate-coloured surface, dip the articles into a boiling solution of sulphuret of potassium. Strong hydrosulphate of ammonia produces a dark tint of oxidation, and if diluted with much water a light tint is produced. Nitric acid produces a light surface. The fumes of sulphur produce a beautiful blue-coloured surface. This operation should be conducted in a closed box, and all parts not to be blackened should be coated with a suitable resist varnish. After any of these processes the articles may either be scratched, or otherwise burnished.
Imitation Silver Alloys.
The undermentioned white alloys have their various uses in the industrial and mechanical arts, some being employed as common silver, whilst others are manufactured as near as possible in imitation of it, and used as a substitute, for many purposes. In melting the alloys in which nickel and several other compounds enter into combination, unless very great care be exercised, it is a difficult matter to maintain the true and definite proportion of each metal of which the alloy proper is composed, owing to the loss of the more fusible metals by volatilization, if allowed to remain too long in the furnace. The best method of preparing the compound for the crucible, is to mix the copper and nickel together. The latter is produced from the pure oxide of nickel; therefore it is taken in this form and placed in the crucible with the copper at the commencement of the operation. When these ingredients are well melted, and incorporated by stirring, add the zinc or other fusible metal required to make up the compound, previously heating it thoroughly over the mouth of the crucible, to prevent the chilling of the already molten metal which it contains. When silver forms a component part in any of these alloys it should be added at the beginning of the process along with those of a high degree of fusibility, and reduced under the protection of a suitable flux; charcoal being the best for the purpose. This flux also tends to preserve the fusible metals, upon their addition to the melted compound in the pot, from too suddenly flying away in the shape of fumes. The best zinc of commerce should be employed in these alloys, which is sold under the name of spelter.
Common silver alloy alloy—
| oz. | dwts. | grs. | |
| Fine silver | 1 | 0 | 0 |
| Shot copper | 0 | 17 | 0 |
| Nickel | 0 | 13 | 0 |
| 2 | 10 | 0 |
Another—