Why does silver tarnish? So the big question is, “Why does silver tarnish?” Sterling silver is an alloy. “What’s an alloy?” You might be thinking. An alloy is a combination of two or more metals such as fine silver and copper. When two or more metals are combined greater strength is achieved. Sterling silver is made of 92 1/2% (.925) silver and 7 1/2% (.075) copper. Fine silver alone is very soft and not a good choice for making jewelry.  Sterling silver is a combination of fine silver and copper and makes a stronger metal to work with. Sterling silver (.925)