Meaning of Precious Metal Stamps & Hallmarks
Metal stamp | Minimum percentage of pure metal | Common alloys**
.925 - Also 925 Sterling Silver | 92.5% pure fine silver | Usually copper
10k - Also: 16, 417, 10KP* | 41.6% pure gold (10 parts out of 24) | Usually silver, copper, zinc, and nickel
14k - Also: 583, 585, 14KP* | 58.3% pure gold (14 parts out of 24) | Usually silver, copper, zinc, and nickel
18k - Also: 750, 18KP* | 75% pure gold (18 parts out of 24) | Usually silver, copper, nickel, and palladium (for white gold)
22k - Also: 916, 917* | 91.6% pure gold (22 parts out of 24) | Usually silver and copper
24k - Also: 999* | 100% pure gold (24 parts out of 24) | None
900 Platinum - Also: 900 Plat, Plat 900, Pt900, 900Pt* | 90% pure platinum (900 parts out of 1,000) | Ruthenium, rhodium, palladium, and other platinum group metals
950 Platinum - Also: PLAT, PT, 950 Plat, Plat 950, Pt950, 950Pt* | 95% pure platinum (950 parts out of 1,000) | Ruthenium, rhodium, palladium, and other platinum group metals
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").
*Alternate stamp or European hallmark
**May vary depending on desired color, such as white gold or rose gold
The modern Hallmarking System started in London, England in the 1300s to protect the public against fraud from unscrupulous sellers. Due to the high value of pure gold, silver and platinum, there is a great deal of temptation to increase profits by reducing the precious metal content of an alloy during the manufacturing of coins, jewelry, flatware, and other valuable metal art objects.
Hallmarking is an official designation that can only be added to an item after it has been assayed to determine its purity by an Assay Office. A hallmarking designation is significantly different than a voluntarily marking of "fineness" that is made by a manufacturer, as there is no way to verify the manufacturer's accuracy.
Metals Hallmark Symbols & System
Traditionally, hallmarks are stamped, or "struck" into the metal using a steel punch, but laser-marking is now replacing the punch method by many Assay offices.
Hallmark symbols consist of four "compulsory Marks." The "date" hallmark became optional in 1998, but the other three symbols are still compulsory. The symbols give the following information:
Sponsor or Maker: Who made the piece.
Standard Mark: The guaranteed standard of fineness or purity.
Assay Office: The Assay Office that tested and marked the item.
Date: The year the item was tested and marked.
The "standard" hallmark indicates the "fineness" or purity of the metal alloy. In the case of Sterling Silver, the "925" Hallmark indicates that there are 925 parts of pure sliver per 1,000 total parts.