What Does PLAT Mean on a Ring?

PLAT is the traditional English-language abbreviation for platinum. Under the US FTC Jewelry Guides, a ring marked simply PLAT or PLATINUM with no qualifying number must contain at least 950 parts per thousand platinum — 95% pure — making an unqualified PLAT stamp equivalent to the numeric PT950 convention used in Japan and much of Asia. Lower-purity platinum alloys must say so, in forms like '900 Plat.' or '850 Pt.'

The mark is especially associated with early 20th-century rings. Platinum became the prestige setting metal of the Edwardian and Art Deco decades — the era of filigree 'orange blossom' engagement rings — because its strength allowed lacework settings and secure, minimal prongs that gold could not match. American rings from this period are often stamped PLAT or 10% IRID PLAT, the latter meaning 90% platinum hardened with 10% iridium, a standard alloy of the day. Platinum jewelry production then largely stopped during the Second World War, when the US declared platinum a strategic metal, which helps bracket a PLAT-marked ring's age.

In Britain, platinum joined the formal hallmarking system in 1975, with an orb symbol and a 950 fineness mark, so British rings from then on carry hallmarks in addition to, or instead of, the word.

As a metal, platinum is dense, naturally white, and hypoallergenic, and it wears by displacing rather than shedding material. A vintage PLAT ring's value rests on its craftsmanship, condition, and stones as much as its considerable metal content.

Look inside the band, where PLAT is stamped alone or in combinations such as PLAT 950, 10% IRID PLAT, or IRIDPLAT, sometimes with a maker's mark and stone-weight notation. On vintage filigree rings the stamp often sits on the shank near the base of the setting and may be worn thin or partially removed by past resizing, so a loupe — or a jeweler's test if illegible — helps confirm it.