Common jeweler’s marks include those that indicate the manufacturer, carat or karat weight, type of metal used and the jeweler. The most important mark is the one indicating the karat or carat weight.
Karat is the unit of weight measurement for precious metals such as gold. This is usually indicated by the number of karats followed by the letter K. Each karat is the equivalent of 1/24th of the whole. For example, the mark 18k means that the piece of jewelry is 18 parts gold and 6 parts alloy such as copper.
The letters KP indicate that the karat of the piece of jewelry has been verified. A 20kp mark therefore means that the piece of jewelry is made from at least 20 karat gold.
Carat is the unit of weight for precious stones, especially diamonds, and is equal to 200 milligrams. A diamond ring that is 1.01 carats is usually marked with the number 1.01 and so on.
Lastly, jeweler’s and manufacturer’s stamps are also common on jewelry. Each jeweler has his own unique mark, usually the abbreviation of the store name or sometimes a business logo. JBR, for example, means that the piece is from J.B. Robinson Jewelers. Manufacturer’s stamps work in the same way, with a T&CO mark meaning that the piece was made by Tiffany & Company.