l-16th of an ounce of verdigris, and the same quantity of finely pounded muriate of ammonia, are to be dissolved in |ths of a pint of rain-water, the solution left standing covered for 3 to 4 hours, and then 14 pint more water poured into it. The copper vessel, which must be perfectly clean, is now to to be held over a charcoal fire until it is equally heated throughout and becomes uniformly tarnished. The copper is now to be rubbed over with the mixture, and then carefully dried. After five or six repetitions of this treatment, the copper receives a brass color; after from six to ten repetitions, it acquires a fine yellow. It the copper is now to be changed from yellow to brown, it must no more be wetted whilst hot; if, however, it be desired to have it very pale brown, the process must be repeated twenty or twenty-five times.— When the desired color isattained, the copper is to be laid in clean water, taking care, however, to clean it or dry it rapidly after taking it out. This must be done carefully. The copper is then held over a weak charcoal fire, when the bronze becomes permanent and fire-prod1. To give a fire-proof, brown bronze color to brass, the following is the process:— 3-32 of an ounce of crystallized verdigris and the same qnantity of sal-ammoniac are mixed with fths of a pint of rain water, and left to stand for 2 to 3 hours. The brass is then to be -rubbed over with it for 2 to 3 minutes, when it becomes green. 1J pints of rain water is now to be added to the solution. The metal is now held over a charcoal fire, which must not be too strong, until it acquires a copper color. It is then again wetted, and left to dry by evaporation. When it has been treated in this manner four or five times, it becomes olive-colored. The heat may now be somewhat increased, but it is necessary to be very careful that the metal does not become too hot. When it has been treated nine or ten times in this manner, it becomes ? brown. AH long as any greenish places are to be seen, however, this treatment must be continued, in many cases 20 to 25 times before the required color is obtained. If, however, the metal be strong, the materials are to be dissolved in hot rain water, and the metal rubbed with it immediately until it acquires a fine dark green color; it is then to be held over a strong charcoal fire, by which means it acquires a fine brown color after 10 to 12 repetitions or the treatment.— It is necessary to be careful that the metal is equally heated throughout. If spots appear, they must be bitten out during the work and polished with brick dust.
This article was originally published with the title "Fire-Proof Bronze" in Scientific American 8, 36, 288 (May 1853)