3615. To Silver Glass

3615. To Silver Glass. An easy and economical process. Mix 90 parts by measure of a solution of Rochelle salts at 1.50 specific gravity, with 900 parts distilled water, and boil them in a flask; drop in carefully 20 parts of a solution of nitrate of silver specific gravity 1.18, and boil again. This solution can be bottled and kept for any length of time. Another fluid has to be prepared by adding ammonia to a solution of nitrate of silver until the precipitate is entirely dissolved; filtering and diluting 1 part of it with 100 parts of water. For use, put equal parts of the two preparations in a suitable vessel, clean the glass well (see No. 3621 (To Clean the Surface of Glass for Silvering)), and immerse it in the mixture until sufficiently coated. The coating of silver should be protected with a coat of lac varnish.

3616. Drayton's Process for Silvering Glass

3616.   Drayton's Process for Silvering Glass. Mr. Drayton mixes 1 ounce nitrate of silver, 3 ounces water, 1 ounce liquid ammonia, and 3 ounces spirit of wine, and filters the solution after it has stood 3 or 4 hours. To every ounce of the solution he adds 1/4 ounce sugar (grape sugar if possible), dissolved in equal quantities of water and alcohol. The surface to be silvered is covered with this liquid at a temperature of 160° Fahr., main-tained till the deposition of silver is complete. When quite dry, the coated surface is covered with mastic varnish. Other substances besides sugar occasion the deposition of silver from the ammoniacal solution; as oil of cassia, oil of cloves, and oth*er essential oils, aldehyde, etc.. Unger recommends a strong alcoholic solution of tannin. He had accidentally mixed in a dish a small quantity of a thick alcoholic solution of tannin with an equally small quantity of a strong solution of nitrate of silver; and in the course of a short time he found the dish coated with a thin, brilliant, and uniform layer of metallic silver. He directly repeated the experiment, and met with the same result again and again. He next proceeded to evaporate the liquid to dryness by placing the dish on the surface of warm sand. As soon as it was completely dry, the coating was found to be so fast on the porcelain that it required the point of a sharp penknife to scrape it off. He also succeeded in producing a brilliant metallic coating from a saturated solution of sulphate of copper by the same solution of tannin.

3617. Pettijean's Process of Silvering Glass

3617.    Pettijean's Process of Silvering Glass. Two solutions are to be prepared. The.first is composed of 261/2 drachms nitrate of silver and 2 ounces aqua ammonia, dissolved in 1 pint of distilled water. After filtration this liquor is diluted with 16 times its volume of distilled water, and, drop by drop, a solution of 1161/4 grains of tartaric acid is added.

The second is prepared in the same manner, but with a double quantity of tartaric acid. As these solutions are rapidly reduced, prepare in the morning the liquors to be used during the day. Before silvering, the glass is perfectly cleaned, first with chalk and a fine cloth, then with a bung and a little of the first solution. It is then rubbed dry with a piece of chamois leather. (See No. 3621 (To Clean the Surface of Glass for Silvering).) The glass, laid horizontally upon a table of cast iron, at a perfect level, is heated (by means of a cast iron water-bath beneath) to 113° Fahr., an India-rubber roller dipped in distilled water is next passed over its surface, and then its surface is covered with No. 1 solution. The deposit of silver commences in about 10 minutes, and is completed in about 15 minutes afterwards. The glass is then tilted up so as to allow the liquor to run off, and rinsed with water rather more than lukewarm to carry away the non-adherent powder. It is then restored to its horizontal position and covered with solution No. 2. In a quarter of an hour the deposit is completed. The next thing is to wash the plate as before, and dry it, after which it only remains to polish and burnish the film of silver deposited, in order to make it perfectly smooth, and give closeness to the grain. To cover a three-feet square of glass requires 5 pints of liquor. The deposit is, therefore, about 11/2 drachms to every 9 square feet. To preserve the coating of silver from sulphura-tion and rubbing, it is covered with a paint made with 1 pound of lead pigment, 11/2 ounces of drying oil, and 51/2 ounces of spirits of turpentine. Liebig has produced the same result by depositing on the silver a coating of galvano-plastic copper, but the advantages resulting from the greatest solidity of the deposit scarcely compensate for the practical inconveniences of the process.