Platinum in Jewelry: Properties, Alloys and Care

Platinum used in jewelry is usually 90 to 95 percent pure, alloyed with small amounts of iridium, ruthenium or cobalt to make it harder and easier to work. It is very dense (about 21.5 g/cm³) and melts at around 1,768°C, which is why it feels heavy in the hand and why bench work on it calls for different solders, torches and eye protection than gold. In the United States, only metal that is at least 950 parts per thousand pure platinum may be marked simply “Platinum.”

Key properties

The Royal Society of Chemistry gives platinum a melting point of 1,768.2°C (3,214.8°F) and a density of 21.5 g/cm³. It is a shiny, silvery-white metal as resistant to corrosion as gold. Most commercially produced platinum comes from South Africa, followed by Russia and Zimbabwe, and its main use is in catalytic converters, not jewelry.

Property	Platinum	950 palladium	Typical 14K or 9K white gold
Density (g/cm³)	21.5 (pure metal)	11.8	About 12.7
Melting point	1,768°C (pure metal)	1,555°C (pure metal)	Varies by alloy, well below platinum
Natural color	White	White	Often rhodium plated to look whiter

The palladium and white gold figures come from the Palladium Technical Manual published by Johnson Matthey and the Goldsmiths’ Company Assay Office London. In practical terms, a platinum ring weighs well over half again as much as the same ring in white gold, and the metal cost reflects that weight as well as the price per ounce.

Purity and US quality marks

The FTC Jewelry Guides (16 CFR 23.6) set out how platinum may be marked in the US. In plain English:

• 950 parts per thousand or more of pure platinum may be marked or described simply as “Platinum.”
• 850, 900 or 950 parts may be marked with the number before the word or abbreviation: “950Pt.,” “950Plat.,” “900Pt.,” “900Plat.,” “850Pt.” or “850Plat.” The accepted abbreviations are “Pt.” and “Plat.”
• At least 500 parts platinum and at least 950 parts platinum group metals (PGM) in total may be marked with the parts per thousand of each PGM, for example “600Pt.350Ir.” or “550Pt.350Pd.50Ir.”
• 500 to 850 parts platinum, without 950 parts PGM (for example “585 Plat.” with cobalt) must be accompanied by a clear disclosure of the full composition and a statement that the product may not have the same attributes as traditional platinum, unless the marketer has competent scientific evidence that it does not differ materially.
• Below 500 parts pure platinum may not be described as platinum at all.

Writing in 1999, Jurgen J. Maerz of Platinum Guild International noted that while some countries allow a small negative tolerance where solder is used, the US tolerance is zero. A separate FTC provision (16 CFR 23.7) says sellers should disclose any surface layer of rhodium on products marked or described as precious metal. This is a summary, not legal advice.

The main jewelry alloys

Platinum alloys are purpose alloys: the best metal for machining a wedding band is not the best for casting a filigree mounting. Maerz’s 1999 Santa Fe Symposium paper identified the most common US alloys as 95 percent platinum with 5 percent ruthenium or cobalt, and 90 percent platinum with 10 percent iridium.

Alloy	Hardness (Vickers, per Maerz)	Best uses	Behavior and cautions
Pt900/Ir100	About 110 HV	General purpose: casting, fabrication, machining	The long-time US “work-horse”; torch-weldable; needs no flux or pickle
Pt950/Ir50	About 80 HV as cast	Hand fabrication and forging	Soft as cast and not recommended for casting; work-hardens well
Pt950/Ru50	About 130 HV	Machined wedding bands, tubing, wire and chain	Difficult to cast; torch melting not recommended; ruthenium oxide fumes are toxic
Pt950/Co50	About 135 HV	Casting, including fine detail	Flows well; slightly magnetic; oxidizes slightly when heated
Pt900/Pd100 and Pt950/Pd50	60 to 80 HV	Soft castings and fine settings, mostly in Asia	Grayish color, so many pieces are rhodium plated

Maerz’s later alloy table for Ganoksin gives similar figures and adds harder heat-treatable alloys, such as platinum with indium and gallium, used for findings where springiness is needed.

Patina, scratches and wear

All precious metals scratch. What differs is what happens to the metal. Platinum Guild International’s technical material, written by Maerz and republished on Ganoksin, explains that a scratch in platinum mostly displaces metal, leaving ridges along its edges, rather than removing it. Metals that lose material when scratched wear down faster, while platinum loses metal at a much slower rate.

Over time, those overlapping fine scratches produce a soft satin look that the trade calls patina. Some owners like it, and PGI describes it as a mark of the metal’s character. Others want the original mirror finish, which a jeweler can restore by polishing.

Two distinctions help when talking to customers:

• Durability is not the same as scratch resistance. Maerz defines durability by strength and scratch resistance by hardness. Platinum is strong and holds stones securely, but a polished surface will still show marks.
• Platinum is a “dead” metal. It holds the position it is pushed into with little springback, which is why prongs stay where the setter puts them.

Bench notes

Contamination

Platinum is unforgiving of stray metal. In Fearless Platinum Repairs, Maerz advises keeping files, sandpaper sticks, buffs and compounds strictly for platinum, because lower-melting metals picked up from gold or silver work can melt into it under the torch. Even a trace of lead can make platinum brittle and unworkable. He recommends tungsten rather than steel tweezers, which can leave dark spots, and an alumina- or zirconia-based ceramic soldering block.

Torches, solders and welding

• Fuel. For melting platinum with a torch, Maerz favors hydrogen and oxygen, with propane and oxygen as a workable alternative. He warns against acetylene, because carbon from the flame can be absorbed by the metal and make it brittle.
• Solders. Platinum solders are named by their flow temperature in Celsius, from about 1000 up to platinum weld at 1773. Above roughly 1,300°C, neither flux nor a protective coating is needed. Lower-temperature “platinum” solders are mostly palladium and silver with no platinum, and Maerz does not recommend them for sizing because they polish out of the seam and leave a visible line.
• Fit. All joints should fit closely. Solder should not be used to fill gaps.
• Cobalt alloys. Maerz recommends sizing Pt/Co rings with 1700 solder and not fire-coating before soldering, since boric acid becomes a contaminant at platinum temperatures. Light oxidation afterward can be cleared by reheating and pickling.
• Laser and pulse-arc welding make it possible to work close to heat-sensitive stones, as in a Ganoksin case study of sizing a channel-set band.

Sizing and retipping

Maerz’s rule of thumb is that one ring size equals about 2.2 mm of shank. He suggests welding in thin platinum stock (about 0.25 mm) or using 1700 solder, and welding the inside of the shank as well as the outside. Heat travels more slowly in platinum than in gold, so careful welds can be made near some stones, but every stone should be checked for fracture filling and damage before heating. For retipping prongs without heating the stone hard, he describes melting a little easy white gold solder on the filed prong tip and flowing it to join a new platinum wire tip.

Polishing

Because platinum moves rather than cuts away, it is harder to bring to a mirror than gold. Maerz’s sequence runs from a #4 then #6 cut file, through 240, 320, 400 and 600 abrasive papers, to a highly polished tungsten carbide burnisher with light oil, then gray, white and finishing rouges. He stresses polishing as much as possible before setting or assembly, and finishing the platinum first when it is combined with gold, since gold polishes faster.

Safety

Platinum work produces intense light at very high temperatures. Maerz recommends #5 gas-welding glasses for short soldering jobs, #6 goggles for longer welding, and #10 or #11 electric welding goggles for casting, and warns that sunglasses give no infrared protection. Avoid breathing fumes when torch-working ruthenium alloys. During finishing, a Bench magazine safety guide republished by Ganoksin recommends a dust and mist respirator, good dust collection, tied-back hair and secured clothing around rotating equipment.

Platinum or white gold?

White gold is a gold alloy whitened by other metals and, in many pieces, finished with rhodium plating, which the FTC Guides say should be disclosed. Platinum is naturally white and does not need plating to stay white, although some soft Pt/Pd products made in Asia are rhodium plated for color.

Consideration	Platinum (950 or 900)	White gold (14K or 18K)
Weight	Much heavier for the same design	Lighter
Color over time	Stays white; develops patina	Plated pieces may need replating as rhodium wears
Wear	Scratches displace metal; slow metal loss	Scratches remove more metal over time
Repair	Needs platinum solders, dedicated tools and dark eye protection	Standard gold bench methods
Price	Higher metal weight per piece	Lower metal weight per piece

Platinum’s place in fine jewelry has shifted over time. Maerz noted that before World War II platinum was the metal of choice for many fine engagement and wedding rings, until it was classified as a strategic metal during the war and white gold gained ground. More recently, Johnson Matthey’s PGM Market Report recorded that platinum jewelry fabrication fell 2 percent to 1.36 million ounces in 2023, its lowest level since the late 1980s, mainly because Chinese consumers moved toward gold.

Common questions

Is 900 platinum “real” platinum? Yes. It is 90 percent pure and may be marked “900Pt.” or “900Plat.” in the US, but it may not be marked simply “Platinum,” which requires 950 parts.

Why does a platinum ring look dull after a year? That is usually patina from everyday scratches. A jeweler can polish it back to a high shine, or the owner can keep the satin look.

Is platinum magnetic? Most platinum jewelry is not, but Maerz notes that platinum-cobalt alloys are slightly magnetic, so a weak attraction to a strong magnet is not proof of a fake.