Platinum 950 vs 900: Alloys, Hardness, Hallmarks and Wear Compared

What is the difference between platinum 950 vs 900?

Platinum 950 (stamped Pt950) contains 950 parts of platinum in every 1,000 parts by weight, so it is 95% platinum. Platinum 900 (Pt900) contains 900 parts, or 90%. That number is the fineness. The remaining 5% or 10% is another metal, added to make an alloy (a blend of metals). Pure platinum is too soft for most rings: it bends, and claws made from it would not hold a stone securely for long. If any of these words are new to you, our glossary of jewellery terms explains them in plain English.

Platinum itself is a dense, grey-white precious metal. Pure platinum has a density of about 21.45 g/cm³, melts at about 1,768 °C and sits around 3.5 to 4.5 on the Mohs scale (a scratch-hardness scale where diamond is 10). Pt950 and Pt900 share these traits closely, so a ring in either feels noticeably heavier than the same ring in gold. Unlike white gold, which is yellow gold whitened with other metals and usually plated with rhodium, platinum is white all the way through. Our comparison of white gold against platinum covers that bigger choice.

Pt950 is the usual standard for rings in Australia, the UK, Europe and the US. Pt900 is traditional in Japan and common in vintage rings, chains and some machine-made jewellery. Both are genuine platinum; neither is plated or watered down in any misleading sense. For a wider look at how the metal is used for rings, pendants and custom work, see our page on platinum jewellery made in Melbourne.

What metals are mixed into Pt950 and Pt900?

The stamp tells you how much platinum is in the piece, but not what makes up the rest. That second metal is what decides most of the practical differences. The common platinum alloys are:

Iridium and ruthenium are both platinum-group metals, close chemical relatives of platinum that are also white and resistant to tarnish. Cobalt is not a platinum-group metal; it is added because it helps molten platinum fill fine detail in a casting mould. The cobalt in a platinum alloy is a small addition and should not be confused with cobalt chrome and tantalum wedding bands, which are a different family of metals altogether.

Some suppliers also make Pt950 with small amounts of copper, gallium or a mix of metals, each tuned for casting, machining or spring hardness. In a workshop, the alloy is chosen to suit the job: a soft iridium alloy for a bezel that is pushed over by hand, a harder ruthenium or cobalt alloy for thin claws that must grip a diamond for decades.

How are platinum 950 and 900 stamped in Australia?

Australia has no compulsory government hallmarking system and no independent assay office. Stamps are applied by the maker, and they are protected by the Australian Consumer Law, which makes it illegal to misdescribe the metal in a piece. That means the stamp is only as reliable as the business that put it there. These are the marks you are most likely to see inside a platinum ring:

• PT950, 950PT or 950 PLAT: 95% platinum.
• PT900, 900PT or 900 PLAT: 90% platinum.
• PLAT or PLATINUM with no number: common on older pieces; the fineness was often 90–95%, but it should be tested to be sure.
• IRIDPLAT: found on vintage rings, meaning platinum alloyed with iridium, often around 90/10.
• A maker's or sponsor's mark: initials or a symbol identifying who made or sold the piece.
• Two metals, such as 18CT & PT: a ring made partly in gold and partly in platinum.

Overseas rules differ. The UK has legally recognised platinum standards of 850, 900, 950 and 999, tested and marked by an assay office. In the US, the Federal Trade Commission allows the word 'platinum' on its own only at 950 and above, with lower fineness shown by number. Japan commonly uses Pt900 and Pt850. Our guide to reading Australian hallmarks and metal stamps covers gold, silver and platinum marks in more detail, and if your ring combines metals, see how stamps work on two-tone and mixed-metal rings.

Is platinum 900 harder than platinum 950?

It depends on the alloy. Vickers hardness (HV) is a lab measure of how much a metal resists a diamond point being pressed into it: the higher the number, the harder the metal. Compared alloy for alloy, more iridium makes platinum harder, so Pt900/Ir is harder than Pt950/Ir. But Pt950 with ruthenium or cobalt is harder again than Pt900 with iridium.

These figures are typical ranges, not fixed values. Hardness rises when metal is hammered, rolled or burnished (called work hardening), and falls again when it is heated. A finished, polished ring is usually harder than the annealed figures above. Gold alloys vary just as much; our page on how 14ct gold alloys are made shows the same principle in gold.

Harder does not mean scratch-proof. Every platinum alloy shows fine scratches with daily wear, because even the hardest sits around Mohs 4 to 4.5. If you want a band that barely scratches at all, you are looking at scratch-resistant tungsten rings, which trade that resistance for being impossible to resize.

How does a platinum ring look and wear over time?

Platinum wears differently from gold. When gold is scratched, a tiny amount of metal is usually lost. When platinum is scratched, most of the metal is pushed aside into a small ridge rather than removed. Over months, those tiny ridges build up into a soft, satin-like finish called patina. Some people like it; others have the ring repolished, which smooths the displaced metal back into place.

• Colour: Pt950 and Pt900 look virtually identical side by side. Both are a cool grey-white, slightly greyer than rhodium-plated white gold. Pt950/Co can look a touch darker.
• No yellowing: platinum does not turn yellow underneath, because there is no gold under a plating layer.
• No tarnish: platinum does not react with air or skin, unlike the darkening described in our guide to why silver tarnishes and develops patina.
• Slow metal loss: bands thin very slowly over decades, but claw tips still wear and should be checked.

Some people ask for platinum to be rhodium plated so it matches the brighter white of plated white gold. It can be done, but the plating wears off in time like any plating and then needs redoing. Our guide to rhodium plating and how often to replate explains the process. For most platinum wearers, polishing every few years is enough.

Is platinum 950 or 900 better for metal allergies?

Both are among the most skin-friendly jewellery metals. Platinum itself very rarely causes contact allergy, and neither Pt950 nor Pt900 normally contains nickel, the most common cause of jewellery rashes and an ingredient in some white gold. Iridium and ruthenium are also very rarely a problem.

The one alloy to think about is Pt950/Co. Cobalt is a known skin allergen. Reactions to platinum-cobalt jewellery appear to be uncommon, because the cobalt is a small share and bound into the alloy, but if a dermatologist has confirmed a cobalt allergy, ask for platinum with iridium or ruthenium instead. For a full list of metals and what to ask, read our guide to nickel-free options for sensitive skin.

Rashes under a ring are not always an allergy. Soap, moisturiser and water trapped under a wide band can irritate skin with any metal, so clean the ring and dry your hands well before assuming the metal is at fault. If you react to most metals, lightweight titanium rings are another low-allergy option, though they cannot be resized easily.

Platinum 950 vs 900: which costs more?

Pt950 contains slightly more platinum, so its metal value is a little higher, but the difference in a finished ring is small. Platinum is traded per troy ounce (31.1 g), and over recent years the fine metal has ranged very roughly from AUD 40 to AUD 80 per gram. A 6 g band in Pt950 holds about 5.7 g of platinum; in Pt900, about 5.4 g. That 0.3 g gap is worth roughly AUD 12–25 at those prices.

What makes platinum jewellery cost more than gold is mostly weight and labour. Platinum is denser, so the same ring weighs more in platinum than in 18ct gold. It also melts at a much higher temperature (around 1,770 °C, against about 1,064 °C for pure gold), needs special casting moulds, and takes longer to finish and polish. Those costs are about the same for Pt950 and Pt900.

These are broad ranges only. Prices move with the platinum market and with the weight, width and design of the piece, so always compare quotes on the same weight in grams.

How does platinum compare with white gold, palladium and other white metals?

Palladium is platinum's lighter cousin: naturally white, nickel-free and only a little over half the weight, which some people find more comfortable in a wide band. See our guide to palladium rings and how they wear. Silver is far softer and tarnishes, so sterling silver jewellery suits fashion pieces better than an everyday engagement ring.

Platinum also turns up in craft pieces: it can be layered with gold in patterned mokume gane rings, though many mokume makers use palladium or silver instead. If you are weighing every option from gold to alternative metals, start with our overview of choosing a metal for an engagement ring.

How do you care for a platinum 950 or 900 ring?

Platinum is low maintenance, and care is the same for both fineness grades:

• Clean at home: warm water, a drop of mild dishwashing liquid and a soft toothbrush, then rinse and dry.
• Check claws: have a jeweller check claws and settings every 6–12 months, even though platinum claws wear slowly.
• Repolish when you like: polishing removes patina; plan on it every few years rather than every year.
• Store separately: platinum and gold rings can scratch each other, and diamonds can scratch platinum, so keep pieces apart.
• Ultrasonic cleaners: safe for the metal itself, but check first if the ring holds treated or fragile gemstones.
• Two-metal rings: keep chlorine away from any gold or solder parts; platinum handles chlorine better than gold does.

How do you choose between Pt950 and Pt900? Step by step

1. Ask the fineness and the alloy. Find out whether it is Pt950 or Pt900, and which metal makes up the rest: iridium, ruthenium or cobalt.
2. Match the alloy to the design. Thin claws and slim bands benefit from a harder alloy such as Pt950/Ru, Pt950/Co or Pt900/Ir; bezels and hand-engraved work suit a softer iridium alloy.
3. Check for allergies. If you have a confirmed cobalt allergy, ask for an iridium or ruthenium alloy.
4. Look at the stamps. Confirm the fineness mark and maker's mark inside the band, and keep any paperwork that states the metal.
5. Compare weight, not just price. Ask for the finished weight in grams so quotes in different metals can be compared fairly.
6. Plan the upkeep. Book a claw check every 6–12 months and decide whether you prefer the patina or an occasional polish.