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Enriching the Surfaces of Silver - JCK 1892
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posted 11-14-2016 09:07 AM
THE JEWELERS’ CIRCULAR
Feb. 17, 1892
Enriching the Surfaces of Silver
By the application of the processes about to be described the finishing touches in their relation to articles or wares of silver manufacture are effected. These processes, as adopted by the trade, are various, almost every firm having a specially prepared mixture and mode of employing it. We shall refer only to those which, from their practical utility, are likely to be of service to those workmen who have to do with this particular method. The branch of the art of which we are now treating comes only into operation when every other process of workmanship has been completed; and some of these processes must be executed in a perfect manner in order to arrive at the highest possible results in this one. The best and richest surface is produced when the metal to be operated upon is good in quality, and the workmanship of a fair order, so far as regards smoothness and freedom from surplus solder marks.
My method for the coloring or whitening I of silver goods is highly simple; the following are the details: A mixture of very dilute sulphuric acid is first provided in the proportion of one ounce to forty ounces of water and well mixed together; the work after being heated to a good red heat is boiled in this, which soon removes the oxide from the surface and shows the fine white color of the real silver. Objects of delicate workmanship are usually annealed by the gas; being placed on a pumice stone of light material, the flame of the gas is blown with the mouth blow-pipe in such a manner that the object gradually becomes heated all over alike, and the work should be well heated, as this facilitates the process of oxidation and subsequently that of, whitening. The oxidation takes place at the expense of the copper in the silver alloy, and this is only affected by raising the articles to a very high temperature, which produces the oxidation of the copper coming in contact with the air and which necessarily exists upon the surface of the alloyed goods. Whitening silver goods, therefore, is nothing more than the removal of the base alloy from the surface, leaving the pure metal behind, with its full rich colors. Therefore to be clear, the process of annealing in contact with cold air oxidizes the copper upon the surface and the pickling mixture so dissolves and removes it that it gradually undergoes a process of refining and is ultimately made to represent the finest material in all its purity.
Sometimes silver work is to be seen having a brown color upon it; this is produced when the acid employed for coloring has been too strong; it can only be remedied by another annealing and boiling out in a much more dilute mixture. The various other methods employed in the trade for the purpose of whitening silver work of the best quality, and allhough annealing is always a part of the process, other ingredients, such as salt and tartar, permanganate of potash, cyanide of potassium, alum, etc., have been severally used for the cleaning or whitening mixture. They may be useful in their application to plated work (articles that have received a coating of pure metal by means of the electro-metallurgical process) for cleansing purposes only, but for all practical purposes the process to which I called special attention is to be much preferred.
Common articles of silver cannot be whitened by annealing and boiling out in a diluted acid; a thin film of pure silver must be deposited upon their surface by the process of electro-deposition, or by the action of some chemical preparation in which fine silver forms the principal ingredient. Such preparation, however, as the latter can be used only to plain surfaces; therefore they are not applicable to ail kinds of work. They are composed of the following chemical ingredients:
II. Chloride of silver 1 part, common salt 1 1/2 parts;
III. Chloride of silver 1 part, prepared chalk 1 part, pearl-ash 1 part;
IV. Chloride of silver 1 part, alum 1 part, common salt 2 parts.
The chloride of silver is easily prepared by precipitating it from the nitrate with a solution of common salt or hydrochloric acid. The various mixtures should be worked up with water into a thin paste and applied to the work by rubbing with a soft cork or piece of wash-leather, or by thoroughly stirring it about in the mixture until it has acquired the requisite degree of whiteness. For the purpose of silvering watch and clock faces, etc., these mixtures may be used with advantage and entire success.
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