Platinum 950 — The International Standard for Fine Platinum
Platinum 950 — The International Standard for Fine Platinum
The UK hallmark fineness and the benchmark of prestige houses
Platinum 950, marked Pt950, is the alloy standard containing 95.0 percent pure platinum and is the international benchmark fineness for fine platinum jewellery. It has been the UK hallmarking standard for platinum since the Hallmarking Act 1973 took effect in 1975, the standard used by leading prestige houses including Cartier, Tiffany, and Patek Philippe, and the de facto reference fineness in the United States, Europe, and the international auction trade. Pt950 represents a deliberate choice of platinum content high enough to deliver the metal's full physical and optical character while permitting the small alloying addition needed for hardness and workability.
Composition and properties
The 5 percent alloying addition in Pt950 is most commonly ruthenium, iridium, or cobalt. Pt-Ru at 5 percent is widely used because it produces a hard, durable alloy with good casting and setting performance. Pt-Ir at 5 percent is the traditional fine-jewellery alloy, harder than Pt-Ru and well-regarded for prong work. Pt-Co alloys cast cleanly and are favoured for intricate cast designs but require care in finishing because cobalt can contribute a faint warm tint if oxidised at the surface.
Density is the highest of any platinum-alloy fineness in routine use — about 21 grams per cubic centimetre — and the colour is the cleanest white. The hardness is sufficient to hold prongs reliably on diamonds and coloured stones; the alloy work-hardens during forming, which both helps with setting strength and demands appropriate annealing during fabrication.
Hallmarking
In the United Kingdom, Pt950 jewellery carries the orb hallmark for platinum alongside the fineness number 950, the maker's sponsor mark, the assay-office mark, and the date letter. The orb mark, introduced when platinum entered the hallmarking system in 1975, is the visual signature of UK-hallmarked platinum and provides the buyer with statutory assurance of fineness. International markets recognise Pt950 by the fineness number and, in many jurisdictions, by additional national marks.
Patina and wear
Pt950 develops a fine matte patina with wear as polished surfaces accumulate microscopic scratches that displace metal rather than remove it — the metal is preserved but the surface texture changes. Some collectors prize the patina for its appearance of age and use; others prefer the high finish and have the piece repolished periodically. Unlike rhodium-plated white gold, Pt950 cannot wear through to a different underlying colour because the alloy is white throughout its volume.
In the trade
Pt950 commands the highest market position among platinum finenesses because it carries the prestige of UK hallmarking, the alloy chosen by leading houses, and the highest practical platinum content for fine jewellery. The cost premium over Pt900 is meaningful at retail because higher platinum content compounds with higher fabrication labour costs to produce a noticeably more expensive finished piece. For coloured-stone settings, signed work, and bridal jewellery destined for the international market, Pt950 is the working standard.