Silver plating is performed for both decorative and functional purposes, it is also applied in electrical engineering to facilitate electrical contacts and thickness contacts for certain engines. It should also be noted that glossy silver has a high reflective power, which makes it suitable for optical applications.
The characteristics of the coatings (hardness, thickness, colour, crystal grain size, etc..) strictly depend on the bath composition, temperature, electrical conditions, and possible mechanical dwell. Silver deposits normally have a milky velvety aspect, easy to polish.
Common baths have a highly variable silver content, which can range from 10 to 25 g/l; normally, it is about 20 g/I. They can also be used for small parts.
Concentrated baths are used for rapid silver plating, in particular devices with cathodes in motion. They can also be used for the continuous processing of wire and tape. Their silver content is about 30 g/l. They can also be used to quickly achieve the so-called strong or heavy silver plating, namely silver plating of significant thickness.
Baths for glossy silver plating provide shiny deposits.
Baths by immersion provide a low silver and free cyanide content. They are used for cheap silver plating on iron ore, copper, and brass. Silver plating takes place by chemical shift, as a result of a simple brief immersion in the solutions.
For quick thickness silver plating, tanks with special equipment designed to impart motion to the cathodes are used. The motion can be back and forth, sinking, rotary, or carousel; the latter involves the use of circular tanks.
Anodes must be made of pure silver foils (usually 1 mm thick) and possess a surface area approximately equal to the one of the objects (smaller by one quarter). They should also be bagged in cotton canvas, terylene, or polypropylene. For light silver plating, especially in the watchmaking industry, very small platinum anodes, immersed in the bath for a short time, are often used. With these anodes, a voltage of 6 8 V must be used.
The temperature of the baths should not be below 18 or 20 °C, otherwise the deposits will be porous. The best electroplating conditions for common baths are at 30 or 40 °C, since at higher temperatures the deposits are not improved and anodes are more soluble. If the baths are too cold, especially in the presence of a lot of carbonate (which originates due to the carbon dioxide in the air), the deposits will be scratched, which means they cannot be polished.
For silver plating of small parts, barrel plating or vibroset devices are used. The use of barrel plating for the electroplating of silver is continually increasing; horizontal immersion barrels with anodes located outside are preferred. For silver plating of small parts, a solution richer in free cyanide is needed, in order to avoid polarization due to the limited anodic area.