Pure silver is relatively soft, so silver is usually alloyed with copper to increase its hardness and strength. However, silver is present naturally in many copper ores, making it an alloy that has been used for thousands of years. The combination of silver and copper is known for its attractive colour, high ductility and ability to be hardened by cold working. Silver’s strength as an alloying element is enhanced by the mechanical and electrical properties of copper. Copper-silvers cannot be hardened by heat treatment. They do not become harder with time and they do not have a ‘shelf life’.
Sterling silver is an alloy created when copper is added to pure silver. 92.5% by weight of silver and 7.5% by weight of other metals, usually copper. When exposed to air, both silver and copper will oxidize. Thus, in melting sterling silver and other silver-copper alloys, care must be taken to prevent oxidation.
Shibuichi is a type of silver-copper alloy. It means “one-fourth” in Japanese and indicates the standard formulation of one-part silver, to three parts copper, though this may be varied considerably according to the desired effect. A wide range of colours can be achieved using the whole range of alloy compositions, even above 50% silver, e.g. 90% copper and 10% silver for a dark grey and down to 70% copper and 30% silver for lighter greys.
These alloys are available in bar, plate, sheet, strip, tube and wire.