How to Test Platinum: Acid, XRF and Density Tests

Platinum can be screened at home with a hallmark check, a magnet and a density test, and confirmed with an acid test, XRF or professional assay. No single home test is conclusive on its own: each check rules certain fakes out and certain genuine alloys in, and only combining two or three of them narrows the answer enough to trust. The sections below walk through each method in rising order of rigor, from a five-second visual check to the fire-assay standard refiners use to settle bullion.

How to Tell If Platinum Is Real#

Telling real platinum apart from a look-alike takes more than one check: a genuine piece usually carries a fineness mark, resists a magnet and a nitric-acid test, and is denser than white gold or silver of the same size. Understanding what each result actually proves starts with platinum purity itself, since a "real platinum" question is really a question about fineness, the parts-per-thousand scale that hallmarks, alloy names and refiner assays all report against. A piece that fails one test is not automatically fake, and a piece that passes one test is not automatically genuine; a Pt950/Co ring, for example, is real platinum that still moves toward a magnet, which is exactly why the table below lists a limitation for every method. Before testing a suspiciously light or unmarked white metal item, it is also worth ruling out platinum-plated jewelry, a base metal with a thin platinum surface layer that can pass a quick magnet or visual check but fails density and, eventually, wear.

Check the Hallmark or Stamp First#

A genuine platinum item is usually stamped "Plat," "Pt" or a number such as "950" or "900," under UK Hallmarking Act or US FTC rules; an unmarked "surface-coated" claim is itself a red flag under 16 CFR Section 23.6. In the United Kingdom, platinum hallmarking has been compulsory since the Hallmarking Act 1973, and only one of the four UK Assay Offices, London, Birmingham, Sheffield or Edinburgh, may apply the mark; the legal fineness standards are 850, 900, 950 and 999 parts per thousand, with 850 the minimum, and items under 0.5 g are exempt from the requirement. The United States takes the opposite approach: there is no compulsory assay office, and marking is self-declared by the maker under the FTC Jewelry Guides, 16 CFR Section 23.6. A US piece marked "Platinum," "Pt." or "Plat." with no number should be at least 950 fine; a piece stamped "950Pt." or "900Pt." carries that stated fineness instead. For the full grade ladder behind these numbers, see 950 platinum, which covers what Pt950 means and how it compares with Pt900 and Pt850. A stamp is a starting point, not a verdict: it can be forged, and in the US it reflects the maker's declaration rather than an independent assay, which is why the checks below matter as a second opinion. Full detail on the marks themselves, assay-office symbols and how to read a date letter, is covered on the dedicated platinum hallmarks page.

Magnet Test: Which Platinum Alloys Respond#

A magnet test is only a rough screen: Pt950/Ru, Pt950/Ir and Pt950/Cu alloys are not attracted to a magnet, but Pt950/Co, a common Asian casting alloy, is slightly magnetic, so a magnetic response does not by itself rule out platinum. The test is genuinely useful in one direction only: a strong, confident pull toward a magnet is a reliable sign that a piece is a ferromagnetic base metal (steel, nickel alloy or a plated fake with a magnetic core), not platinum in any common jewelry alloy. A weak or absent pull, however, proves nothing on its own, because it is consistent with every platinum alloy in the table above and with several non-magnetic base metals besides. Readers who want the full picture of which platinum alloys and which look-alikes respond to a magnet, and why, should see is platinum magnetic, the dedicated page on this question. The practical rule for 950 platinum pieces specifically: know which hardening metal is stamped or declared, because that single fact, ruthenium or iridium versus cobalt, decides whether a magnet test is even meaningful for that particular ring.

Density (Specific Gravity) Test#

Platinum is denser than gold, silver or white gold of the same size: pure platinum weighs about 21.45 g per cubic centimeter against roughly 19.3 g for gold and 12.6 to 16.9 g for 14K to 18K white gold, so a piece that feels too light for its volume is not platinum. The test itself, specific gravity by water displacement, weighs the item first in air, then suspended in water; the weight lost in water is the volume displaced, and dividing the air weight by that lost weight gives a specific-gravity number to compare against the reference values below.

Because the gap between platinum and 14K white gold is nearly two to one, density is one of the more decisive home checks: a ring that should weigh noticeably more than an equivalent white gold ring, and does not, is very unlikely to be platinum. The main sources of error are gemstones, which displace volume without adding platinum-level mass, and hollow settings or filled shanks, which do the same in the other direction; a solid, stone-free section of metal gives the cleanest reading. For the underlying physical-constants context, including how platinum's density compares across the full platinum group, see platinum density.

Acid Test: Why Platinum Resists Nitric Acid#

Platinum resists plain nitric acid, the reagent that dissolves silver and lower-karat gold on contact, because only aqua regia, nitric acid combined with hydrochloric acid, dissolves platinum; no reaction to a nitric-acid test is a meaningful positive sign. At small and secondary-refining scale, aqua regia dissolves platinum and palladium as chloro-complexes, while rhodium, iridium, ruthenium and osmium are largely refractory and report to the insoluble residue rather than dissolving; at industrial refinery scale, dissolution instead uses chlorine gas sparged into hot hydrochloric acid, a more selective process than aqua regia. A jeweler's acid-test kit applies a drop of nitric acid to a small scratch on the metal: silver darkens or dissolves visibly, low-karat gold reacts, and genuine platinum shows no visible reaction at all, which is why the test is a standard part of a pawnbroker's or jeweler's kit alongside a touchstone. A frequently searched home alternative, testing platinum with hydrogen peroxide, has no documented protocol in refining or assay literature; treat any hydrogen-peroxide method as an unverified folk test and rely on the sourced nitric-acid result instead. Vinegar, another household acid sometimes proposed for the same purpose, is addressed directly in the FAQ below.

XRF Testing#

XRF (X-ray fluorescence) identifies a metal's composition in seconds without damaging it, and jewelers, pawnbrokers and scrap yards use it as a fast screening tool for platinum and its alloys. A handheld XRF gun reads the characteristic X-ray signature of each element in the sample and reports a composition breakdown, platinum, the alloying metal and any plating layer, without cutting, scratching or dissolving anything, which is why it has largely replaced the acid touchstone at high-volume buy counters.

XRF is a screening tool, not a settlement assay: its readings are sensitive to surface plating and particle size and require matrix-matched calibration, so refiners do not accept an XRF result to settle a bullion transaction. A thin rhodium or platinum plating over a base alloy can read as much higher purity than the bulk metal actually is, because the X-rays sample only a shallow surface layer; a reading that looks too good on an unusually cheap piece is a reason for more testing, not less.

Professional Assay: How Refiners Verify Platinum#

Refiners confirm platinum purity by fire assay, not XRF: nickel-sulphide fire assay collection is the standard method for the full six-platinum-group-metal suite, and LPPM Good Delivery bars must pass a five-figure assay determination of at least 99.950% fine. Lead-collection fire assay, the classical technique, works well for gold and can determine platinum and palladium, but it does not reliably collect rhodium, iridium, ruthenium and osmium; nickel-sulphide fusion collects all six because the resulting button captures the whole platinum-group suite in one step. For wholesale bars and ingots, the London Platinum and Palladium Market applies its Good Delivery Rules: an accredited refiner submits sample plates to an independent referee laboratory, and the refiner's own five-figure assay determination, not less than 99.950% fine, must agree with the referee's result before the bar is accepted. For the grade ladder this standard sits at the top of, alongside industrial and investment-grade platinum below it, see platinum purity grades.

Professional verification generally runs in order:

1. Screen with XRF for a fast composition read at intake.
2. Confirm with fire assay, nickel-sulphide collection for the full PGM suite, where a defensible fineness number is required.
3. Referee-check against an independent LPPM laboratory for bars entering or leaving Good Delivery custody.

Platinum Wire in the Flame Test: a Different Meaning of "Platinum Test"#

"Platinum wire" in a flame test is chemistry-class terminology, unrelated to jewelry testing: a platinum wire loop holds the sample in the flame because platinum's melting point, 1,768.3 degrees C, is far above a laboratory flame and it resists chemical attack from the reagents. A flame test identifies which metal ion is present in a sample by the color its vapor gives a flame, sodium's yellow, copper's blue-green and so on, and the wire itself is just the sample-delivery tool: it must not melt, must not react with the test solutions, and must not itself add a color to the flame that would contaminate the reading. Platinum's chemical inertness and high melting point make it the standard choice for that loop, the same underlying properties, resistance to chemical attack and a very high melting point, that make platinum useful across a wide range of industrial and laboratory platinum uses far beyond jewelry. This chemistry-class sense of "platinum test" has nothing to do with authenticating a ring or bar and should not be confused with the identification methods above.

Related Platinum Purity Pages#

Platinum's purity, fineness and identification are covered across five related pages: 950 platinum, for the meaning of the most common jewelry alloy; platinum hallmarks, for reading assay-office marks; platinum purity grades, for the industrial and investment-grade ladder above jewelry fineness; platinum-plated jewelry, for identifying a plated item rather than solid metal; and does platinum tarnish, for how a genuine piece ages over time. Current bid and ask levels for platinum and the other five platinum group metals are on platinum group metal prices today.

Platinum Testing FAQ#

Can vinegar be used to test for platinum? Vinegar does not react with platinum: platinum resists all common household acids and only dissolves in aqua regia, so a vinegar test shows no reaction on genuine platinum. That non-reaction is the same underlying resistance the nitric-acid test relies on, just with a much weaker acid, so a vinegar test is not sensitive enough to distinguish platinum from several other white metals that also fail to react with it.

Can you pawn or sell tested platinum jewelry? Yes: pawnbrokers and scrap buyers value platinum on its confirmed weight and purity, the same basis used at selling platinum jewelry for scrap, once a hallmark, density or acid test, or an XRF reading, has confirmed the metal. A buyer will typically still run their own check, most often XRF, before quoting a price, since the tests above narrow the answer but a purchase decision usually rests on the buyer's own verification.

What are platinum's symbol, atomic number and CAS number? Platinum has the symbol Pt, atomic number 78 and CAS number 7440-06-4. Its full properties, occurrence and uses are covered on platinum (Pt), element 78.