Glossary

Hallmark

A hallmark is an official stamp on jewelry indicating the metal's purity (e.g. 750 for 18k gold, 925 for sterling silver), maker, and assay-office origin. Tiny, often a few hundred microns wide, but legally and commercially significant — sellers must show it clearly when present, and AI must preserve it pixel-faithfully.

What's in a hallmark?

A complete hallmark typically includes: a purity number (750 = 18 karat gold, 585 = 14k, 925 = sterling silver, 950 = platinum), a maker's mark (the goldsmith or brand identifier), and an assay-office stamp (the testing authority that verified the purity — varies by country: anchor for Birmingham, leopard's head for London, fineness mark for Paris). Some pieces also carry date letters indicating the year of assay. The stamps are usually pressed into a discreet area — inside a ring band, behind an earring post, on a necklace clasp.

Why hallmarks belong in catalog photos

For higher-value pieces, buyers look for the hallmark as proof of metal purity claim. A listing that says "18k gold" without a visible 750 hallmark on the photo creates buyer doubt; a listing that shows the stamp closes the proof loop without the buyer needing to ask. Marketplaces vary: eBay buyers in particular scrutinize hallmarks. For a $1,200 listing, a clear hallmark in the photo set is worth more than a fifth ring shot.

What AI must do (and not do) with hallmarks

Hallmarks are tiny — at typical photo resolution they're maybe 20-40 pixels wide. The most common AI failure on hallmarks: treating them as dust or scratches and "cleaning them off." That's catastrophic — the seller's own purity claim photo just lost its proof. Jewelry-aware AI is told upfront that hallmark stamps must be preserved exactly. If the input has a hallmark, the output has the same hallmark, in the same place, at the same legibility. Generic AI tools can't make this guarantee.

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Last updated 2026-05-03