To explain, let’s first go back to Silver, or Pure Silver. Silver’s purity carries a numeric designation based on 1,000. Pure silver usually carries a 999 rating. In its purest form silver is very soft.
To improve functionality and durability, pure silver is mixed with other metals (usually copper). Sterling silver contains 92.5 percent silver and 7.5 percent copper or other alloy.
Since the mid-19th century, sterling silver is marked as such. It is either stamped with the word “sterling,” or it may be stamped with “925.”
The copper is the component that makes the silver harder and more durable, but also causes tarnish over time. Tarnish is the result of the copper reacting to oxygen in the air. You can help to reduce tarnish on your sterling silver jewellery by storing it in an air tight container when not in use.