What exactly is sterling silver made of? Sterling silver is defined as 92.5% Czysty srebro, and the rest another alloy metal such as copper, żelazo, or steel. . 7.5% different metal improves the durability of the finished material. This combination is ideal because fine jewelry is soft and prone to bending and breaking. Sterling silver does not simply mean that the piece is plated with silver that will eventually rub off.