Identify and Characterise Platinum Alloys

Quality Assurance Benchmarks highlight workmanship of semi-finished and finished jewellery. Learn how to identify and characterise platinum alloys.

Front view of platinum “J” hoop earrings designed by Erik Stewart, featuring a variety of small, bezel-set coloured stones and circles of different sizes that use negative space as a design motif.

Different alloy combinations have their own unique working properties and characteristics, and are best suited to specific manufacturing methods

Common platinum alloy ingredients contain other platinum group metals such as ruthenium, iridium and palladium

At 100% purity, platinum is too soft for jewellery use. For jewellery, platinum is typically used as an alloy containing 95% platinum and 5% other metals.

Side view of a platinum band designed by Michael Bondanza, featuring diamonds channel-set into a curved top.

For products that consist of at least 950 parts per thousand (ppt), these products can be described and marked as platinum or an abbreviation of the word (PLAT)

According to US Federal Trade Commission guidelines, all platinum jewellery should be marked to indicate the purity of the product

Perspective view of a princess cut solitaire with diamonds set in the shank. The hallmark for 90% Platinum Iridium, 900 Pt Ir, is visible in the lower inside of the shank.

90% Platinum alloyed with 10% Iridium is hallmarked as 900 Pt Ir

900 Pt Ir is a universal alloy that is used for many manufacturing applications

900 Pt Ir has machining limitations due to the lower hardness of 100HV

Perspective view of a platinum band with diamonds. The hallmark for 95% Platinum Cobalt, 950 Pt Co, is visible in the lower inside of the shank.

95% Platinum alloyed with 5% Cobalt is hallmarked as 950 Pt Co

950 Pt Co is an excellent alloy for casting

950 Pt Co is ferromagnetic, so it is attracted to magnets

950 Pt Co oxidises at 1000 °C

950 Pt Co has a hardness of 135HV

Perspective view of a round solitaire with diamonds set in the split shank. The hallmark for 95% Platinum Ruthenium, 950 Pt Ru, is visible in the lower inside of the shank.

95% Platinum alloyed with 5% Ruthenium is hallmarked as 950 Pt Ru

950 Pt Ru is an excellent all-purpose alloy that is ideal for fabricating, machining and casting

950 Pt Ru has a hardness of 135HV

Identification of Specific Platinum Alloys

When altering platinum jewellery, it is important to work with like platinum alloys that match the original piece.

Perspective view of a platinum ring designed by Sylvie, featuring a flower-shaped diamond halo surrounding a large centre diamond, and diamonds set halfway down the shank.

Many jewellers do not know the differences between platinum ruthenium and platinum cobalt when sizing rings, and use the wrong platinum materials such as laser wire or solder when sizing rings. This can result in the attempted work failing due to compatibility differences.

Because most platinum alloys are composed of other platinum group metals, the similarity between platinum group combinations can easily lead to errors

Precise analysis of specific platinum alloys can only be accomplished in a precious metals testing laboratory