Pt850 platinum is a platinum jewellery alloy containing 850 parts per thousand of pure platinum (85%), with the remaining 15 per cent composed of alloying metals — typically palladium, iridium, or ruthenium. The grade sits at the boundary above which most international hallmarking regimes recognise the platinum mark; jurisdictions such as the United Kingdom and Japan accept Pt850 as platinum, while jurisdictions and trade conventions in the principal Western fine-jewellery markets generally favour Pt950 or Pt900.

Properties

The 15 per cent alloying-metal content increases hardness modestly relative to Pt900 and significantly relative to Pt950, with corresponding gains in wear resistance for prong and structural use. The trade-off is reduced platinum nobility, lower tarnish resistance, and a slightly less white colour than higher-fineness alloys. The cost saving per finished piece is real but moderate, since the dominant cost driver in any platinum piece is platinum itself rather than the alloy formulation per se.

In the workshop

Pt850 alloys are workable in a conventional platinum workshop with standard tools, soldering temperatures, and finishing procedures. The alloying-metal content varies by manufacturer and by intended application: Pt850Pd is softer and more castable, Pt850Ir is harder and better suited to prong work, and Pt850Ru sits in between. Most Pt850 jewellery is produced from pre-mixed casting grain rather than alloyed in-house.

In the trade

Pt850 platinum is uncommon in fine-jewellery markets in North America, where Pt950 is the de facto standard. The grade appears more frequently in Japanese-market jewellery and in some European markets where lower platinum fineness is accepted under local hallmarking regulations. For buyers, the practical advice is to confirm the stamped fineness on any piece described as platinum and to understand that not all platinum-marked pieces are equivalent in platinum content.

Further reading

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