Sterling silver has a purity of 92.5 percent, whereas pure silver has 99.9 percent silver content. Sterling silver is also more durable than pure silver, which is why it is often used for jewelry and utensils.
Sterling silver is an alloy of pure silver. Because pure silver, also known as fine silver, is too soft to make into jewelry, other metals are added to make it harder and more durable. Sterling silver is made when metal experts add various metals such as nickel, copper and zinc, making the jewelry more durable. 92.5 percent is sterling silver and the other 7.5 percent consists of the added metals. Apart from jewelry, other items that are made from sterling silver are everyday utensils and silverware, such as spoons, forks and knives.
Even though sterling silver is stronger than pure silver and can remain stable in oxygen and water for long periods of time, it is more prone to tarnishing. Tarnishing happens when chemicals in the air, like sulfur, meet with the added metals and causes a reaction. Pure silver is like gold -- it does not tarnish even when in constant contact with air and water.
Oftentimes, jewelry is marked as "sterling silver plated," which means the actual jewelry is made of a metal, like nickel or copper, but is coated with a layer of sterling silver, which wears off over time and can tarnish sooner.