Jewelry Hallmarks and Metal Stamps: The Professional’s Reference Guide
Hallmarks and metal stamps are the language of jewelry authentication and quality representation. They appear on virtually every piece of fine jewelry — stamped into shanks, clasps, and gallery walls in marks so small they require magnification to read — yet they communicate essential information about metal purity, manufacturing origin, and legal compliance. A jewelry professional who cannot read and interpret these marks is missing a fundamental tool for product authentication, customer service, and the accurate representation of merchandise that ethical selling requires.
Gold Hallmarks and Karat Stamps
The karat system (US and Americas)
In the United States and most of the Americas, gold purity is expressed in karats on a 24-point scale representing pure gold. Common stamps and their meanings:
24K or 999 — Pure gold (99.9%); too soft for most jewelry applications
22K or 916 — 91.6% gold; used in some traditional jewelry markets (India, Middle East)
18K or 750 — 75% gold; the fine jewelry standard in most of the world
14K or 585 — 58.5% gold; the most common standard in US commercial jewelry, durable and cost-effective
10K or 417 — 41.7% gold; the minimum legal “gold” designation in the US
9K or 375 — 37.5% gold; the UK and some European minimum standard
The millesimal fineness system (Europe)
European jewelry often uses millesimal fineness stamps — a three-digit number representing parts per thousand of pure metal. 750 means 750/1000 = 75% gold (18k equivalent). 585 means 585/1000 (14k equivalent). 375 means 9k equivalent. When reading European jewelry, the three-digit stamp is the primary purity indicator.
Platinum Hallmarks
Platinum stamps indicate the alloy composition in parts per thousand. Common stamps:
PT950 or PLAT950 — 95% platinum, 5% other PGM (ruthenium or iridium); the fine jewelry standard
PT900 — 90% platinum; also used in fine jewelry, slightly denser than 950
PT850 — 85% platinum; less common, requires qualified descriptor under FTC guidelines
PT or PLAT alone — implies at least 950 purity under FTC guidance when used without a numeric qualifier
Silver Hallmarks
Sterling silver is 925/1000 pure silver and is stamped 925 or STERLING. Coin silver (900/1000) appears on antique American pieces stamped 900 or COIN. Britannia silver (958/1000) is found on some fine British pieces. Silver-plated items should be stamped EP (electroplated), EPNS (electroplated nickel silver), or similar indicators — the absence of a sterling or fineness stamp on what is presented as silver jewelry is a significant red flag.
Maker’s Marks and Assay Office Marks
Maker’s marks
Many jewelry pieces carry a maker’s mark — initials, a symbol, or a registered trademark indicating the manufacturer or designer. In antique and estate jewelry, maker’s marks are critical for attribution and value assessment. Cartier, Tiffany, Van Cleef and Arpels, and other luxury houses stamp their pieces with distinctive marks that significantly affect value and must be verified for authenticity in resale or estate transactions.
British hallmarking system
The British assay system, administered by four assay offices (London, Birmingham, Sheffield, Edinburgh), is one of the world’s most comprehensive hallmarking systems. A fully hallmarked British piece carries: the sponsor’s mark (maker), the metal fineness mark, the assay office mark (anchor for Birmingham, leopard’s head for London, etc.), and the date letter indicating year of assay. Reading British hallmarks allows precise dating and attribution of antique British jewelry.
Country of Origin Stamps
Many pieces carry country of origin stamps: “Made in Italy,” “750 IT,” French eagle’s head poincon (for 18k gold), Russian star with 585 or 750 (for Soviet-era gold), and many others. Country stamps matter for: attribution of antique and estate pieces, import compliance, and marketing (Italian craftsmanship, Swiss watchmaking). They also provide authentication context — a piece stamped with a Soviet-era poincon is verifiably pre-1991, regardless of what a seller claims.
Identifying Non-Precious Metals and Plating
Pieces made of base metals with gold or silver plating carry specific indicators: GF (gold-filled, a thick mechanical bonding of gold to base metal), GP (gold-plated, thin electrodeposited gold), GE (gold electroplated), RGP (rolled gold plate), SS (stainless steel), and many others. The FTC requires that plated items not be described as “gold” or “silver” without the qualifying “plated” descriptor. Being able to identify these stamps prevents misrepresentation and protects both the seller and the customer.
