Hallmarks & Metal Stamps Guide
Decode the tiny stamps inside your jewellery. Look up any mark instantly, or browse the full reference tables for gold, silver, platinum, plated pieces, and UK assay offices.
What Is a Hallmark?
A hallmark (or metal stamp) is a small mark punched, stamped, or laser-engraved into a piece of jewellery to indicate the purity of the precious metal it's made from. The practice dates back to 1300 in England, when King Edward I required gold and silver items to be tested and marked at an official assay office before sale — making it one of the oldest consumer protection systems in the world.
Modern hallmarks use one of two systems: karats (24 = pure gold, 18K = 75% gold) or millesimal fineness (parts per thousand — 750 = 75%, 925 = 92.5%). Many countries require fineness marks by law; the United States does not legally require purity stamping, though most reputable manufacturers stamp their pieces voluntarily.
Where to Find Hallmarks on Jewellery
Hallmarks are typically stamped in inconspicuous locations to preserve the piece's appearance: inside the ring band, near the clasp on necklaces and bracelets, on the post or back of earrings, and on the reverse of brooches and pendants. Because these stamps are often under 2mm tall, a jeweller's loupe or a smartphone macro camera is usually needed to read them clearly.
Solid Gold vs Plated: Why the Distinction Matters
The single most common point of confusion — and the one with the biggest financial consequences — is the difference between solid gold and gold-covered base metal. A stamp reading "18K" alone typically means solid 18 karat gold throughout. But a stamp reading "18K GP" or "18K HGE" means only a microscopically thin layer of 18K gold has been applied over a much less valuable base metal — the piece has little to no melt value despite carrying the same karat number.
Buyer's tip: Always look for letters after the karat number. No letters generally means solid metal. Letters like GP, GE, GEP, HGE, or RGP mean plated. GF (gold-filled) sits in between — a thicker, mechanically bonded layer that lasts far longer than plating but still isn't solid gold.
No Hallmark? That Doesn't Automatically Mean Fake
A missing hallmark doesn't necessarily indicate a counterfeit. Older pieces made before hallmarking laws took effect, items below a country's legal weight threshold for mandatory marking, and handmade pieces from regions without hallmarking requirements can all be genuine without a stamp. Hallmarks can also wear away over decades of polishing. When in doubt, professional testing (acid test, XRF analyzer, or specific gravity testing) is the only definitive way to confirm metal content.
Working With Casa Jewels
All jewellery manufactured by Casa Jewels is stamped to international fineness standards for the metals and alloys used in each piece. If you're a brand or reseller sourcing manufactured jewellery, we can advise on the correct hallmarking standard for your target market.
Also see our Metal Weight Calculator and Metal Price Calculator for related tools.