We've mentioned this topic briefly a couple of times in other posts but since we have had some questions lately on the topic, here's a summary.
By definition, "sterling" contains 92.5% pure silver. The other 7.5% is made up of some alloy. Why is it not 100% silver? Because the piece would be too soft to use - the alloy adds strength.
The most common alloy is copper. Other metals may be used such as platinum, zinc and germanium but copper remains most popular. Silicon and boron may be used as additives.
The reason other formulas are being tried is to reduce the effects of tarnish and other problems. It's primarily the copper that is reacting with oxygen and sulfur to cause tarnish, not the silver. You may see some advertising in this regard by some manufacturers.
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