Pt900 platinum is a platinum jewellery alloy containing 900 parts per thousand of pure platinum (90%), with the remaining 10 per cent composed of alloying metals — typically palladium, iridium, ruthenium, or cobalt. Pt900 is the dominant platinum standard in Japan and is widely accepted across other markets as a legitimate platinum grade. The alloy occupies a middle position between the harder Pt850 grades and the softer Pt950 standard.

Properties

The 10 per cent alloying-metal content gives Pt900 noticeably greater hardness and wear resistance than Pt950, which is the principal practical advantage for prong-set work. The alloy retains platinum's white colour, corrosion resistance, and hypoallergenic character, with only a fractional reduction in colour purity compared to Pt950 when both are finished to comparable polish. Specific gravity is close to that of pure platinum, in the range of 21 g/cm³.

The choice of alloying metal affects the alloy's specific properties: Pt900Ir is harder and more spring-tempered, Pt900Pd is softer and more castable, Pt900Ru sits in between, and Pt900Co offers excellent casting flow at the cost of weak ferromagnetism. Workshops select the formulation to match the intended use of the piece.

In the trade

Pt900 platinum is the standard fine-jewellery grade in Japan and is widely used in continental Europe and parts of Asia. It is less common in the United States, the United Kingdom, and Canada, where Pt950 is the dominant expectation for fine jewellery. Pt900 is suitable for all conventional jewellery applications, including settings for diamonds and coloured gemstones, wedding bands, and statement pieces. Buyers acquiring platinum across international markets should confirm the stamped fineness on each piece.

Further reading

• GIA Gems & Gemology — platinum standards
• International Gem Society — platinum metallurgy
• GIA Gem Encyclopedia — metals and settings