Platinum Purity: Fineness, Hallmarks, Alloys and Testing

What Is Platinum Purity?#

Platinum purity is the proportion of pure platinum in a metal object, expressed as millesimal fineness (999.5 = 99.95% pure) rather than the karat system used for gold. Millesimal fineness counts parts of pure platinum per thousand parts of total mass, so a fineness of 950 means 950 parts platinum and 50 parts alloy metal in every 1,000 parts, and the system covers platinum, palladium and bullion generally.

Platinum group metal prices today, for platinum, palladium, rhodium, iridium, ruthenium and osmium, sit alongside this purity guide on platinum group metal prices today, since fineness and market price both start from the same identity: platinum, element 78.

The parts-per-thousand system itself is defined in full in DailyPlatinum's millesimal fineness glossary entry.

Platinum Fineness and Purity Marks#

Platinum jewelry and bullion are marked with a fineness number such as 999, 950, 900 or 850, each representing parts of pure platinum per thousand. The table below lists the fineness marks most often seen on platinum, with the approximate purity, the typical product and the standard body behind each one.

925 is the millesimal fineness for sterling silver, not a platinum grade; it is listed here only because it is sometimes mistaken for one.

Karat, spelled with a K, measures gold purity in twenty-fourths, where 24K is pure gold and 18K is 750 fineness; carat, spelled with a C, is a gemstone mass unit equal to 0.2 grams. Platinum uses neither scale: every mark in the table above is a millesimal fineness number. The most widely sold jewelry grade, 950 platinum (Pt950), is covered in full on its own page.

The next mark down in fineness, 900 platinum and other platinum alloys, carries more alloy metal and suits harder, lower-cost settings than Pt950.

Is Platinum Jewelry 100% Pure Platinum?#

Platinum jewelry is not 100% pure platinum: a Pt950 ring is 95% platinum alloyed with ruthenium, iridium or cobalt for hardness and castability. The World Platinum Investment Council's glossary states that platinum jewelry purity "is invariably expressed in parts per 1,000," and names Pt950 as "the most common variant," with the rest of the alloy made of metals such as cobalt or copper. Pt950/ruthenium and Pt950/iridium are the standard European and Japanese bridal alloys, while Pt950/cobalt is used mainly for casting. Each alloy metal raises hardness and improves the platinum's casting flow, properties pure platinum lacks alone. A full breakdown of these blends is on platinum jewelry alloys.

How to Check Platinum Purity#

Platinum purity is checked by acid testing, XRF analysis or density measurement, each covered in detail on DailyPlatinum's testing guide. A jeweler, refiner or assay office chooses among four common methods, listed below.

• Test the metal's reaction to nitric acid, which does not attack genuine high-fineness platinum but etches lower-fineness alloys.
• Scan the piece with an XRF (X-ray fluorescence) analyzer for a non-destructive fineness reading.
• Weigh the piece and measure its volume by water displacement to calculate density, since platinum alloys are far denser than most base-metal look-alikes.
• Send the piece to an assay office or refiner for a certified fineness result.

Only assay or XRF analysis gives an exact fineness figure; acid and density tests only narrow the range. The full procedure for each method, including what a home test can and cannot prove, is on how to test platinum.

Platinum Purity Standards: UK, US and LPPM#

The UK Hallmarking Act 1973 permits four platinum fineness standards, 850, 900, 950 and 999, with 850 as the legal minimum for an article sold as platinum, according to GOV.UK, Assay Office London and Birmingham Assay Office. Palladium hallmarking became compulsory in the UK in 2010 (GOV.UK), extending the same mark system to a second platinum group metal.

In the United States, the FTC's Guides for the Jewelry, Precious Metals, and Pewter Industries, 16 CFR Part 23 section 23.7, are read as setting 950 parts per thousand as the threshold for marketing an article as "platinum" without qualification, with the 850 to 950 tier requiring a qualifying disclosure. DailyPlatinum could not retrieve the primary eCFR text to confirm that wording, so the threshold is reported, not independently verified.

At the wholesale level, the LPPM Good Delivery standard sets 99.95% (999.5 fineness) as the minimum for platinum and palladium plates and ingots weighing 1 to 6 kilograms, according to the LPPM Good Delivery Rules, June 2020 edition. A Good Delivery plate from any of the 39 LPPM-listed platinum refiners settles against any other without re-assay, because Good Delivery accredits the refiner, not just the metal.

The full range of grades between jewelry alloys and LPPM bullion is set out on platinum purity grades, and how assay offices test and stamp each piece is explained on platinum hallmarks.

Platinum vs White Gold: Purity and Alloy Content#

Platinum and white gold differ in purity because white gold is a gold alloy plated with rhodium, while platinum jewelry is used at or near its natural white color. White gold starts as yellow gold, alloyed down to 750 fineness (18K) or 585 fineness (14K) with white metals such as palladium, nickel or silver, then plated with rhodium to hide the alloy's warmer tone. Platinum jewelry needs no such plating: a Pt950 or Pt900 piece keeps its own white color for life, while rhodium plating on white gold wears with handling and needs re-application. A full comparison of density, durability and price is on platinum vs white gold.

Platinum Purity Topics#

DailyPlatinum's purity section covers nine topics, from specific fineness grades to testing methods and plating, listed below.

• 950 platinum (Pt950): the standard bridal and fine-jewelry grade, covered above.
• 900 platinum and other platinum alloys: the jewelry alloy one step below Pt950.
• How to test platinum: acid, XRF and density testing methods.
• Platinum purity grades: fineness grades from 999.5 down to industrial levels.
• Platinum hallmarks: the marks and assay offices that certify fineness.
• Platinum jewelry alloys: the ruthenium, iridium and cobalt blends used in Pt950 jewelry.
• Does platinum tarnish: patina and scratches from wear, on does platinum tarnish.
• Platinum plating: what a plated, not solid, piece contains, on platinum-plated and rhodium-plated metals.
• Palladium jewelry: the 950 and 500 palladium alloys sold alongside platinum, on palladium jewelry.

Platinum Purity FAQ#

What is the purity of platinum?#

Platinum's purity is expressed as millesimal fineness, most commonly 999.5, 950 or 900 parts per thousand. The number counts parts of pure platinum per thousand parts of total mass, the same convention used for palladium and bullion generally.

Is 950 platinum pure?#

Platinum marked 950 is 95% pure, above the UK's 850 legal minimum and below the LPPM's 99.95% wholesale Good Delivery standard. The remaining 5% is an alloy metal such as ruthenium, iridium or cobalt, added for hardness and castability rather than to disguise a lower-value metal.

How much is platinum worth by weight and purity?#

Platinum's value by weight depends on both its fineness and the live spot price, calculated on DailyPlatinum's platinum value calculator. A Pt950 piece pays out on 95% of its gross weight and a Pt900 piece on 90%, once the spot price and any dealer spread are applied to the platinum content alone. Estimate a piece's value on the platinum value calculator.

How do I test platinum at home?#

Platinum purity can be checked at home with a magnet, a density test or an acid-testing kit, though only assay or XRF gives an exact fineness. Platinum is non-magnetic, so a magnet that pulls at a piece points to a base-metal fake, and a home acid kit reacts differently on lower-fineness alloys than on Pt950 or higher. Neither method replaces a certified reading. The full set of tests, including density measurement, is on how to test platinum.

What are platinum's symbol, atomic number and CAS number?#

Platinum has the symbol Pt, atomic number 78 and CAS number 7440-06-4. Those three identifiers appear on every DailyPlatinum page that discusses the element, and its full properties, uses and history are covered on platinum (Pt), element 78.

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