Most jewelry items made of precious metal are stamped with information about the purity level of the metal content. Generally the stamp is placed in an inconspicuous place on the item so it does not detract from the design. Stamps will usually be located on the inside of the band on a ring, on the post or basket setting on a pair of earrings, on the bail (the part that the chain slides through) on a pendant, and on the connecting ring or the clasp on a necklace or bracelet. All jewelry stamps adhere to strict guidelines set by the Federal Trade Commission.
The table below lists the most common precious metal stamps, their alternative stamps or hallmarks, their purity level, and alloys commonly used.
Ruthenium, rhodium, palladium, and other platinum group metals
*Alternate stamp or European hallmark
**May vary depending on desired color, such as white gold or rose gold
The term "karat" (usually abbreviated as "k," "K," or "Kt") refers to the relative purity of gold; pure gold is 24 karats. "Karat" is different from "carat," which is a metric unit of weight for gemstones.
In the context of gold jewelry, "plumb" is an old-fashioned term that means that the fineness or purity level of the gold content is precisely what is stamped on the item. The word "Plumb" or the letter P still sometimes follows the metal stamp (e.g. "14k Plumb," "14KP").