The purity of the metal determines how malleable the silver is and how quickly it will tarnish. 100% Pure Silver is too soft to use for most functional objects including jewelry. Sterling Silver is 92.5% pure silver and is considered a precious metal. The remaining 7.5% of the alloy is usually copper, which adds strength while still preserving the ductility and appearance of the pure silver. Sterling Silver is harder than pure silver and is more durable for jewelry.