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Silver Baths

For ordinary plating 7 pennyweights of fine silver (II pennyweights of nitrate of silver, or 9 pennyweights of chloride of silver), is dissolved in a solution of 33 grains of 98 per cent potassium cyanide in 1 quart of water. For heavy silvering of knives, forks, etc., a stronger bath is used: 17 1/2 pennyweights of fine silver (I oz., 4 pennyweights of chloride of silver, or 1 oz. 15 grains of cyanide of silver,) is dissolved in a solution of I oz. 15 pennyweights of 98 per cent potassium cyanide in 1 quart of water. No accurate statement can be made in regard to the quantity of potassium cyanide in the bath, as it depends on the strength of the current used. With a very weak current, and consequently slow precipitation, somewhat more potassium cyanide may be used than with a stronger current and more rapid precipitation. The anodes, for which fine silver is used, will indicate by their appearance whether the bath contains too much or too little potassium cyanide. They should become gray during silvering, and gradually resume their white color after the interruption of the current. If they remain white during silvering, the bath contains too much potassium cyanide, and, if they turn black, and retain this color after the interruption of the current, potassium cyanide should be added.

The article to be silvered should be moved constantly to avoid the formation of streaks. Before silvering the metals must be prepared by amalgamation. This is done by dipping the articles, previously freed from grease, as explained above, in a dilute solution of mercurous nitrate (30 to 150 grains per qt.) allowing them to remain in the solution only long enough to become uniformly white. Rinse them in water, brush off with a clean soft brush, and immediately place in the striking bath.

Silvering of iron and steel is best accomplished by using a striking solution made as follows: 3/4 of an oz. of C. P. chloride silver, 6 oz. C. P. cyanide of potash, 1 gallon water. After thoroughly cleaning hang the articles for a few minutes in the solution, using a large silver anode surface. The hydrogen gas should escape freely from the surface of work and as soon as covered with a yellowish deposit of silver, which is very adhesive, transfer to the standard solution, which can be made from the concentrated solution. From this no gas should escape, and the anode surface should be about the same as surface of work. A Bunsen or three Smee batteries connected for intensity can be used for the striker, and one Smee cell for standard solution, zinc surface of same equalling that of work.

The articles remain in the bath from ten to fifteen minutes, when they show a uniformly white surface; they are then taken out, scratch-brushed with a brass brush to see that the deposit adheres, all grease removed, and then placed in the bath. After the current is shut off, the articles should be left in the bath a few seconds to prevent the deposit from turning yellow. If the articles are not to be burnished, but are to be left with a mat as they come from the bath, they must be thoroughly rinsed in water without coming in contact with the fingers or the sides of the vessel, then dipped in clean hot water and hung up to dry. They then should be coated with a colorless laquer to prevent turning yellow. If the articles are to have a polished surface, they are to be finally scratch-brushed with frequent moistening with soap-root, dried in warm sawdust and burnished with a steel or stone burnisher.