Source: Precious Metal Information Provided by Americangemsociety.org
The word gold, used by itself, means all gold or it can refer to “pure” gold, meaning 24 karat (24K) gold. Because 24K gold is soft, it’s usually mixed with other metal jewelry called alloys to increase its hardness and durability. If a piece of jewelry is not 24 karat gold, the karat quality should accompany any claim that the item is gold.
The karat quality marking tells you what proportion of gold is mixed with the other metals. Fourteen-karat (14K) jewelry contains 14 parts of gold, mixed in throughout with 10 parts of an alloy metal. The higher the karat rating, the higher the proportion of gold in the piece of jewelry.
Jewelry should be marked with its karat quality. Near the karat quality mark, you also should see the name or
the U.S. registered trademark of the company that will stand behind the mark. The trademark may be in the
form of a name, symbol or initials. If you don’t see a trademark accompanying a quality mark on a piece of jewelry,
look for another piece.
Platinum is a type of precious metal jewelry that costs more than gold. It usually is mixed with other similar metals, known as the platinum group metals: iridium, palladium, ruthenium, rhodium and osmium.
Different markings are used on platinum jewelry as compared with gold jewelry, based on the amount of pure platinum in the piece. The quality markings for platinum are based on parts per thousand. For example, the marking 900 Platinum means that 900 parts out of 1000 are pure platinum, or in other words, the item is 90% platinum and 10% other metals. The abbreviations for platinum — Plat. or Pt. — also can be used in marking jewelry.
The words silver or sterling silver describe a product that contains 92.5% silver. Silver products sometimes may be marked 925 which means that 925 parts per thousand are pure silver. Some jewelry may be described as silverplate: a layer of silver is bonded to a base metal. The mark coin silver is used for compounds that contain 90% silver. According to the law, quality-marked silver also must bear the name or a U.S. registered trademark of the company or person that will stand behind the mark.