Gold Hallmarks and Marks: Reading Karats, Crowns and Convention Stamps

Gold marks answer the two questions every inherited jewelry box asks — how pure, and is it solid? — in a few stamped millimeters. Here's the decoder, system by system.

The purity numbers

Two languages say the same thing:

• Karat marks: 24K pure; 18K = 75%; 14K = 58.3%; 10K = 41.7% (US legal minimum to call it gold); 9K = 37.5% (UK/Commonwealth tradition).
• Millesimal (thousandths): 999, 750, 585, 417, 375 — the same purities in continental notation. A "585" ring IS 14K.

Adjacent finds: "PLAT"/"950" (platinum), "925" (sterling silver — often gold-plated when yellow), and maker/sponsor initials beside the purity.

The words that mean 'not solid'

The value cliff lives here: GF or "1/20 12K GF" (gold-filled — a bonded layer, better than plate but a fraction of solid), RGP (rolled gold plate), GP/GEP/HGE (electroplate), "gold tone" (no gold to speak of), and vermeil (gold on sterling). None are worthless; all are priced as decoration plus base, not as gold weight.

National hallmark systems

Britain assays gold like silver: purity mark plus town mark and date letter (same grammar as silver hallmarks) — a British 18ct piece can be dated to the year. France stamps an eagle's head for 18K; other nations use their own devices; the modern Common Control Mark (scales motif) travels internationally. Pre-1900 and non-Western pieces may carry regional systems or nothing — absence of marks on genuinely old gold is common, not damning.

When marks are missing or suspicious

Marks wear off, sizings cut them away — and fakers stamp brass "18K" daily. Beyond the stamp: weight (gold is dense — brass "gold" feels toy-light), magnet test (gold never attracts; steel springs and clasps legitimately do), wear points (plated pieces show base metal at edges and high spots — check with a loupe), and for real answers, acid/electronic testing or a jeweler's XRF reading, cheap and definitive. On antique pieces, resist testing visible surfaces — test discreet spots and preserve patina.

Antique jewelry context

Karat fashions date pieces: high-karat richness in Victorian work, platinum-and-18K in Deco, 9K in British sentimental jewelry. And on antiques, craftsmanship value can dwarf metal value — a signed period piece is worth multiples of its melt, which is where proper identification and the Antique Identifier app's reads on style, settings and marks earn their keep before anything visits a scale.

The bottom line

Numbers state purity (585 = 14K), letters state construction (GF/GP = not solid), national stamps add dates — and weight, magnets and wear points audit the claims. Read the marks first; melt-value math last.

Values mentioned in this guide are indicative ranges from public auction and marketplace results; condition, provenance and market timing move them substantially. For insurance or estate purposes, get a written appraisal from a certified appraiser.