Japanese Gold and Platinum Marks: K18, Pt900 and the Mint Hallmark
Turn over almost any piece of Japanese jewellery and you will find a short stamp: K18, Pt900, SV925. These marks are the quickest way to understand what a piece is made of, and Japan's conventions differ from those of Europe and America in useful ways. This guide explains them.
Gold: the K marks
Japan states gold purity in carats with a K before the number.
- K24: pure gold, 99.9 per cent, used for ingots, coins and some traditional objects.
- K22: about 91.7 per cent gold.
- K18: 75 per cent gold, the standard for fine jewellery in Japan; equivalent to the European 750 mark.
- K14 and K10: 58.5 and about 41.7 per cent, used for more affordable pieces.
Colour suffixes appear too: K18WG is white gold, K18PG pink gold, K18YG yellow gold.
Platinum: the Pt marks
Japan is one of the world's great platinum markets. Wedding and engagement rings have traditionally been made in platinum rather than white gold, and older Japanese jewellery uses it widely.
- Pt1000 or Pt999: pure platinum.
- Pt950: 95 per cent platinum, common in modern pieces.
- Pt900: 90 per cent, the classic Japanese standard for rings.
- Pt850: 85 per cent, common in chains, where a harder alloy is needed.
Silver
SV925 or 925 means sterling silver. SV1000 is fine silver. Older Japanese silver may be marked jungin (純銀, pure silver) in characters.
The suffix to watch: GP and GF
K18GP means gold plated, and K18GF or GF means gold filled: a base metal with a layer of gold. These marks look like solid gold marks at a glance. Read the whole stamp, every time.
The Japan Mint hallmark
The Japan Mint offers a voluntary assaying service for precious-metal articles. Pieces that pass are stamped with a hallmark combining the Japanese flag, a fineness figure and a shape that identifies the metal. The mark is independent proof of purity, and older Japanese jewellery that carries it is especially trusted. Not all genuine pieces carry it, because the service is optional.
Ring sizes
Japanese ring sizes run by number, from small sizes around #1 upward, and do not match American, British or European scales. When we describe a ring, we give the Japanese size and the inner diameter in millimetres so that you can compare it with a ring you already own.
Questions collectors ask
Is Pt900 better than Pt950?
Neither is better; they are different alloys. Pt900 is slightly harder, and was the Japanese standard for decades.
What if a piece has no stamp?
Some antique and hand-made pieces were never stamped. Testing can confirm the metal. Ask before buying.
Does the Japan Mint hallmark appear on foreign brands?
Rarely. Brands such as Cartier, Tiffany and Bvlgari use their own marks, such as 750 or 925.