The purity of gold is based upon the karat system of measurement. Very simply, gold that is used for jewelry is usually alloyed (mixed) with other metals, such as copper or nickel.
This makes the gold more durable for jewelry use by hardening the gold. In its purest form, gold is 24KT. This is the highest purity measurement for gold. Most jewelry in the U.S. is sold in either 18KT, 14KT or 10KT purity. This means that the gold is mixed with other metals, usually copper or nickel to strengthen the gold. Pure gold is easily scratched and bendable. As an example, 14KT gold jewelry is about 58.3% pure, and the rest is the alloy. All companies pay based on the karat purity weight of the gold.
The biggest difference is that sterling is alloyed (mixed) with another metal, such as nickel or zinc to harden the silver for everyday use. Sterling silver is 92.5% pure silver, while fine silver is 99.9% pure. All companies pay based on the silver purity and weight of the silver item. A common hallmark you will find on sterling silver jewelry is ’925′. Most sterling is used in a variety of jewelry as well as silverware, flatware and decorative candelabra.
Both platinum and palladium are part of the platinum metals group. Both are considered hard metals, so they are usually only alloyed 5-10%. Both metals are also naturally white in appearance. Jewelry made in platinum will be hallmarked with PLAT or PLT. Palladium jewelry is usually hallmarked PLD or PALL.