Palladium is a platinum-based precious metal and one of the rarest precious metals in the world. It has the characteristics of high temperature resistance, corrosion resistance and wear resistance, and presents a silver metallic luster. PA999 is a palladium alloy, which contains 99.9% palladium and 0. 1% other metals, such as platinum and silver. Palladium is widely used in jewelry, electronics, chemical industry and other fields because of its rarity and uniqueness. In the field of jewelry, the symbol of palladium jewelry is usually "PA" or "PD", while PA999 is a palladium jewelry containing 99.9% palladium.