Platinum Alloys

In jewellery, like other precious metals platinum is mixed with other metals to form alloys. Before 1975 there was no requirement for platinum to be assayed and hallmarked in Britain, therefore there was no recognised standard. Because of this, most early pieces marked "plat" or platinum, may be of very variable, and quite low fineness, and most would fail modern assay standards.

Platinum has been hallmarkable in Britain since January 1st 1975. From then until January 1st 1999, the only officially recognised standard of purity or "fineness" in Britain was 950 parts per 1000. From this year, there are now four standards, which are:- 850 900 950 999 parts per thousand. Typically platinum is alloyed with copper, iridium, palladium, rhodium, osmium or titanium.

The following table gives some typical platinum alloy compositions, shown in parts per thousand.