Platinum: denser than gold, whiter than white gold, never plated, and unmistakable on a scale.
The international marks for platinum, standardised at 950 for unqualified use6 checks
Platinum marks are the easiest precious-metal marks to verify, for one reason: platinum is extraordinarily dense. Pure platinum's specific gravity is 21.45, against gold's 19.3 and silver's 10.49. A platinum ring in the hand feels wrong in a way nothing else does, and next to an identical white gold ring the difference is unmistakable.
The marks themselves come in a few forms. PLAT and PLATINUM are the traditional American stamps; 950, PT950 and 950 PLAT are the modern millesimal forms; 900 PLAT and IRIDPLAT appear on earlier twentieth-century American work alloyed with iridium. In the United States, anything marked platinum without qualification must be at least 950 parts per thousand, with lower finenesses requiring the fineness to be stated.
The other thing worth knowing is that platinum is not plated. Its whiteness is the metal, so a platinum ring never needs rhodium replating and never turns yellow — which is the single most useful practical difference from white gold, and the reason it costs more to buy and less to keep.
The comparison people actually want is platinum against white gold, because they look identical in a shop window and behave completely differently over twenty years. Density settles which is which; the rest of the table explains why the price differs.
Note that platinum is softer than 14 karat white gold in the sense that it scratches more readily, but it is far more ductile: it displaces rather than losing material, so a scratched platinum ring can be burnished back where a gold one has lost metal permanently. That is why antique platinum settings survive with their stones intact.
| Property | Platinum (950) | 18k white gold |
|---|---|---|
| Density | About 21.4 — the heaviest common jewellery metal | About 15.5 |
| Colour | The metal itself is white-grey | Alloyed pale, then rhodium plated |
| Maintenance | Never needs replating | Rhodium replating every one to three years |
| Scratching | Scratches, but metal displaces rather than being lost | Metal is lost permanently |
| Hypoallergenic | Yes, and usually nickel-free | Nickel alloys are a common irritant |
| Common marks | PLAT, PLATINUM, 950, PT950, 900 PLAT | 750, 18K, 18KT |
| Purity when marked | 950 minimum unqualified in the US | 75% gold |
| Relative cost | Higher per piece — denser, so more metal by weight | Lower |
The density difference is the whole test. Two visually identical rings, one platinum and one white gold, differ in weight by roughly a third.
A stamp is a claim, not a property. These are ordered by how much each one settles about the metal underneath — and the first two need nothing but a loupe and good light.
This is decisive and needs no equipment beyond a hand. Platinum at 21.4 density is about a third heavier than 18 karat white gold and more than twice as heavy as silver for the same volume. If you can put a platinum-marked ring on a scale and compare it against a white gold ring of similar size, the difference is obvious. A PLAT-stamped piece that feels light is not platinum.
Platinum's whiteness is intrinsic, so a genuine platinum piece never develops the warm yellow-grey cast that white gold gets when its rhodium wears. A ring stamped PLAT that has gone faintly yellow at the shank is white gold, or plated. This is a very fast check on any worn ring.
'PLAT' alone in the United States implies at least 950 parts per thousand. Lower finenesses must state the number — 900 PLAT, 850 PLAT. What to watch for is 'PLATINUM PLATED', 'PLAT OVERLAY' or a mark combining platinum with a base-metal disclosure, and also 'platinum-coloured' or 'platinum finish' in a description, which are colour claims rather than metal claims.
Platinum acid testing is different from gold's and requires a specific reagent; XRF reads it directly and non-destructively. A UK piece may also carry an assay office mark and the platinum orb symbol, which is an independent guarantee — platinum has been part of compulsory British hallmarking since 1975.
Platinum is not magnetic. Neither, importantly, are the metals it is usually alloyed with — iridium, ruthenium, palladium. Any magnetic response points to a steel core or a base-metal substitute. As with the other precious metals, passing this proves only that it is not ferrous.
Platinum is ductile, so wear pushes metal aside into fine raised burrs and produces a soft satin patina rather than removing material. Under a loupe, an old platinum ring shows a dense network of shallow scratches with slightly raised edges. White gold loses metal instead, so its scratches are cleaner-cut and the shank thins measurably over decades.
Platinum fraud is less common than gold fraud, and the reason is instructive: the density is so distinctive that a substitution is easy to detect and hard to disguise. There is no cheap metal with platinum's density, so a fake either feels wrong or has to be built around something exotic.
The realistic risks are therefore two. First, white gold or silver stamped PLAT, which the weight exposes immediately. Second, and much more common in practice, is not fraud at all but confusion: buyers assuming a white metal ring is platinum when it is rhodium-plated white gold, then being surprised when it yellows.
One genuine historical note: a lot of early twentieth-century American jewellery is marked IRIDPLAT or 90% PLAT 10% IRID, meaning platinum alloyed with iridium. That is entirely genuine platinum work from the period and often very fine.
Each of these is checked differently. The ones with their own page have enough that is specific to them to be worth reading separately.
Metal value first, because it is the floor and it is easy to calculate. Anything worth more than melt is worth it for the maker, the age or the design — never for the stamp.
| What you have | What it is worth | Note |
|---|---|---|
| A PT950 ring, 6 g | 5.7 g of platinum at spot | Platinum spot has often traded below gold since the 2010s |
| A 900 PLAT Art Deco setting | Well above melt | Period work carries the value |
| 'Platinum plated' base metal | Nothing | A coating |
| White gold sold as platinum | The gold value only | Check the weight |
Platinum's spot price has spent much of the last decade below gold's, which surprises people who remember the reverse. A platinum ring still costs more to make than a gold one of the same design because it is denser, so more metal by weight goes into it.
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.