95% platinum, the modern international standard. The mark most new platinum carries.
The international marks for platinum, standardised at 950 for unqualified use4 references
For your own ring, Ring Identifier: Jewelry Value — Lovenhall’s jewelry & ring identifier app, free to try on iPhone & iPad — reads the setting and stones together from a photo and gives an indicative range.
PT950 is 95 percent platinum with the balance usually ruthenium, iridium or cobalt, and it is the standard for modern platinum jewellery worldwide. The alloying metal is chosen for working properties: cobalt alloys cast well and take a high polish, ruthenium alloys are harder, iridium alloys are traditional and very ductile.
The 5 percent matters less than it would in gold because the usual partners — ruthenium and iridium from platinum's own group, cobalt from outside it — are white metals too, so the alloy keeps platinum's colour. That is why platinum needs no plating at any fineness.
In the United Kingdom platinum has been subject to compulsory hallmarking since 1975, so a British piece should carry a sponsor's mark, the 950 fineness figure and an assay office mark, often with the platinum orb symbol. Below 0.5 grams the exemption applies.
PT950 · 950 · 950 PLAT · Pt 950
Establish which of these you are holding before judging it. A genuine piece read against another reference's rules will look wrong when it is not.
These apply to this model and not to the rest of PLAT / 950. Work them alongside the maker's general checks, not instead of them.
PT950's density, between about 20.0 and 21.5 depending on the alloy, is unmatched by any plausible substitute at jewellery prices. Compare against a known white gold piece of similar size: the platinum should be roughly a quarter to a third heavier.
Platinum has been compulsorily hallmarked in the UK since 1975. A British piece above 0.5 grams should carry a sponsor's mark, 950, and an assay office mark, often with the orb symbol.
Across a counter the two are hard to tell apart; on a hand they part company within a year or two. 18K white gold is 75 percent gold bleached pale with palladium or nickel and finished with rhodium to reach a cold white. PT950 is 95 percent platinum and white through its whole thickness, so there is no coat to wear away and nothing to renew.
The difference you can measure is weight. Pure platinum has a density of 21.46 g/cm³, and worked from the pure-metal figures the last 5 percent leaves PT950 between about 20.0 and 21.5, cobalt at the light end and iridium at the heavy. A palladium-bearing 18ct white gold is listed by its maker at 16.2 g/cm³. The same ring in PT950 is therefore roughly a quarter to a third heavier — more metal by weight, which is much of why it costs more before a stone is set.
Neither is the better metal in the abstract. Platinum keeps its colour and, when it scratches, moves metal aside rather than losing it; white gold costs less and is restored to white by a replating that is routine and inexpensive. The choice is between paying once and paying a little, often.
| PT950 | 18K white gold (750) | |
|---|---|---|
| Precious metal | 95% platinum | 75% gold |
| The other part | 5% — usually ruthenium, iridium or cobalt | 25% — palladium or nickel, with other metals |
| Colour | White through the metal | Pale warm grey beneath rhodium plating |
| Upkeep | No plating to renew | Rhodium replated as it wears |
| Density | About 20.0–21.5 g/cm³, by alloy | About 16.2 g/cm³ (palladium alloy) |
| The same ring weighs | About 24–33% more | The baseline |
| Marks | PT950, 950, 950 PLAT, Pt 950 | 750, 18K, 18KT |
PT950 densities are worked from PubChem's pure-metal figures at 95 parts platinum to 5 of the partner metal; cast and worked pieces vary a little. The white gold figure is one maker's published palladium alloy — nickel white golds differ.
Three numbers, two metals. 950 and 900 are parts per thousand of platinum; 925 is parts per thousand of silver, a different metal on a different price scale. Within one metal a higher number means a purer alloy. Across metals it means nothing at all — a 925 ring is not a slightly lesser 950 one, and S925 is simply sterling with an S for silver in front.
The United States draws the platinum line in its rules. The Federal Trade Commission's Jewelry Guides let a piece be called platinum with no number only at 950 parts per thousand or above; at 900 or 850 the figure has to lead the word, as in 900 Plat. So PT900 is not a shortfall from PT950 but a smaller, correctly declared fineness — and on early twentieth-century American work, often a platinum-iridium alloy sought for its settings.
In the hand, silver gives itself away. Pure silver's density is 10.5 g/cm³, about half of PT950's, so a sterling ring feels light beside platinum of the same size long before anyone reads the stamp.
| Mark | What it is | The rest of the alloy | Plating and tarnish | US marking rule |
|---|---|---|---|---|
| PT950 | 95% platinum | 5%, usually ruthenium, iridium or cobalt | None needed; platinum does not oxidise in air | May be sold as platinum with no number |
| PT900 | 90% platinum | 10%, often iridium on older American pieces | None needed; behaves as PT950 does | The number must come first: 900 Plat, 900 Pt |
| 925 / S925 | 92.5% silver | 7.5%, usually copper | Tarnishes yellow, then brown, then black | Sterling — a silver standard, outside the platinum rules |
All three are claims until the metal is tested. How to test a PT950 stamp follows below.
No to both, in ordinary wear. Platinum does not oxidise in air at any temperature, so a PT950 ring cannot darken the way sterling does, and because the metal is white all the way through there is no plating to wear off or renew.
What it does instead is age. Fine scratches gather into a soft satin patina, and because platinum pushes metal aside rather than shedding it, a jeweller can polish that patina back to a bright finish — or leave it, as many owners prefer.
Two qualifications. Platinum is not untouchable: PubChem lists halogens, cyanides, sulphur and caustic alkalis among the few things that attack it, which is reason enough to take a ring off for bleach. And a ring stamped PT950 that has turned faintly yellow at the shank should be read as a warning — that is the colour of worn rhodium on white gold, not of platinum.
Yes. A stamp is a few strokes of a punch and costs almost nothing to strike, so PT950 on its own proves only that somebody struck it. In the United States no assay office checks the metal first: the mark is the maker's own claim, which the Federal Trade Commission's guides govern but nobody examines before sale. A British hallmark is a different order of evidence — an assay office tested the piece before marking it, the Birmingham office by reading its platinum content with X-ray fluorescence, and the full mark carries a sponsor's mark, the 950 fineness and the office's own mark.
Where the stamp stands alone, the metal has to answer for itself. In order of what each check settles:
As metal, it is arithmetic: weight in grams × 0.95 × the day's platinum spot price per gram. A 6 g band holds 5.7 g of fine platinum. Spot is quoted per troy ounce, so divide the quote by 31.1035 for the per-gram figure. No price is printed here: spot moves through the trading day, and a figure fixed into this page would be wrong before you read it.
That melt figure is the most a buyer pays for the ring as metal, and few pay all of it. On the conventional bands the Metal Value Calculator uses, a refiner pays about 90 to 97 percent of melt, a dealer 70 to 85 percent and a pawn or high-street counter 40 to 65 percent — so the same 5.7 g fetches very different sums depending on whose counter it crosses.
Anything above melt comes from the rest of the ring — the stones, the maker, the age, the workmanship — and that is a matter for an appraiser, not a formula. What this page gives is an orientation, never an appraisal and never a quotation.
Priced by weight and workmanship. Denser than gold, so a comparable ring uses more metal.
An orientation for honest, unrestored condition — never an appraisal, and never a quotation.
Lovenhall RingThe mark tells you what the metal claims to be. The instrument reads the setting and the stones together and gives a range to orient you — before anyone charges you for an appraisal.