A jewelry alloy is any malleable (capable of being formed or bent into different shapes), ductile (easily molded) base metal that is added to a precious metal to improve its corrosion resistance and other properties.alloys Jewelry  change the properties of the precious metal, including its elasticity, flexibility, hardness and color.
Gold Alloys
Gold is used in jewelry because it can be molded to form any shape. Pure 100 percent gold is soft and rarely used in jewelry making. Gold is alloyed with other metals to improve its strength and malleability. Gold alloys that are commonly used include 18K yellow gold (where K refers to karat or the purity of gold), 18K white gold (also called nickel white gold) and18K palladium white gold. 18K yellow gold combines 75 percent gold with zinc and/or cobalt, silver and copper. It is the most common gold alloy used in jewelry making around the world. 18K white gold is 75 percent gold alloyed with zinc and/or palladium, nickel and copper. White gold jewelry requires rhodium plating since it wears down and deteriorates with extended use. 18K palladium white gold is a combination of 75 percent gold with 25 percent palladium. It is more expensive than white gold and wears down with heavy wear. Other types of gold alloys used in jewelry include green gold (an alloy of gold and silver) and rose gold (an alloy of gold and copper).
Platinum Alloys
Platinum is used in jewelry making for its hypoallergenic properties. It is corrosion and wear-resistant, ductile, malleable and dense. The four platinum alloys commonly used in jewelry making in the United States include Pt950/Ir, Pt950/Ru, Pt900/Ir and Pt950/Co. Pt950/Ir is an alloy of 950 parts of platinum with 50 parts of iridium. Pt950/Ru alloys 950 parts of platinum with 50 parts of ruthenium. Pt900/Ir combines 900 parts of platinum with 100 parts of iridium. Pt950/Co is an alloy of 950 parts of platinum and 50 parts of cobalt.
Silver Alloys
Silver is a shiny white metal that is used to make utensils, tableware and jewelry. It is malleable, ductile and harder than gold. Silver is alloyed with copper to make sterling silver. Sterling silver (7.5 percent copper and 92.5 percent silver) is used to make body jewelry, belt buckles, cuff links, bracelets, necklaces and rings. Other silver alloys used in jewelry include vermeil, Mexican silver, and Britannica silver. Vermeil is an alloy of gold, sterling silver and other metals. Mexican silver is an alloy of 95 percent silver and 5 percent copper, while Britannica silver alloys 95.84 percent silver with 4.16 percent copper.