Base Metal - Any non-ferrous metal excuding precious metals.  Common non-ferrous metals include aluminum, tin, copper, nickel, and zinc. Pewter - A metal alloy, traditionally between 85 and 99 percent tin, with the remainder consisting of 1-15 percent copper, acting as a hardener, with the addition of lead for the lower grades of pewter, which have a bluish tint. Sterling Silver - An alloy of silver containing 92.5% pure silver and 7.5% other metals, usually copper.  Fine silver (99.9% pure) is generally too soft for producing functional objects, and in Sterling the silver is usually alloyed with copper to give strength while preserving the ductility of the silver and a high precious metal content.