Jewelry is most commonly made with metals such as gold, platinum, titanium, silver and stainless steel. Gold, silver and platinum are classified as precious metals, making them more valuable and desirable because they are less reactive, possess a higher luster and are easier to work with than most metals.
Gold is classified by karats. Karats denote the purity and value of the gold. The purest gold is 24 karat at 99.9 percent pure. Pure gold is commonly mixed with alloy metals such as copper and zinc because it's too soft to use in jewelry. These metals are used to make gold jewelry more durable, and they can also be used to change the color of the gold to white gold or rose gold.
Much like gold, silver is often mixed with other metals because it's soft and easily damaged. It's not classified by karat, but there are several types of silver based on purity, such as fine silver (.999 percent pure), sterling silver (92.5 percent pure) and silver plate (a layer of fine silver placed over a base metal).
Platinum jewelry is more expensive and considered more precious than gold. Platinum is commonly mixed with other metals in jewelry as well, but platinum jewelry must be 95 percent pure or it's classified as a platinum alloy.