Platinum is a dense, naturally white precious metal used for fine jewelry, especially diamond rings. Most platinum jewelry is 95 percent pure, marked 950 or PT950. It does not need plating to stay white, rarely irritates skin and holds gemstones securely, though it costs more than white gold and develops a soft gray patina with wear.
Platinum as a metal
Platinum is the best known of the six platinum-group metals, part of the larger family of noble metals. It resists corrosion and does not tarnish in air. Its melting point is high, about 1,768 °C, which made it very hard to work until the nineteenth century and still requires special torches and casting equipment today.
The metal is dense, at about 21.45 g/cm³, about twice as dense as silver and heavier than gold at about 19.3 g/cm³. A platinum ring weighs noticeably more than the same ring in 14K or 18K gold. Many buyers like that weight in the hand.
Platinum has a cool gray-white color. Unlike white gold, it does not depend on rhodium plating for its color, so the color does not wear off.
Purity standards
Platinum jewelry is usually much purer than gold jewelry. The common standards are:
| Mark | Platinum content | Notes |
|---|---|---|
| 950, PT950, PLAT | 95 percent | The usual jewelry standard |
| 900, PT900 | 90 percent | Common in Japan and older American pieces |
| 850, PT850 | 85 percent | Used in some countries and older jewelry |
| 999 | 99.9 percent | Mainly bullion; very soft |
The other 5 to 10 percent is usually another platinum-group metal such as iridium or ruthenium, or sometimes cobalt or copper. Each alloy behaves a little differently. Platinum-iridium is a classic choice for hand fabrication. Platinum-ruthenium is harder and suits machine work. Platinum-cobalt casts well and is slightly magnetic.
Under US Federal Trade Commission guides, an item can be sold simply as "platinum" only if it contains at least 95 percent platinum. Below that, the mark must state the platinum content, such as "900Plat." or "850Plat.", and some mixed alloys must list each platinum-group metal they contain. The hallmarks guide covers these rules and the UK platinum hallmarks.
Patina and wear
Platinum scratches. When it does, metal is pushed aside to form a groove and a small ridge, and very little is lost. Over months of wear, these tiny scratches build up into a soft, satiny gray look called patina. Some people prize it as a sign of age and character. Others have it polished back to a bright shine.
This behavior differs from gold, which loses small amounts of metal to abrasion over decades. A platinum ring keeps more of its original weight, and a jeweler can push displaced metal back into place during polishing. Platinum is not harder than gold in a simple sense. Its strength in jewelry comes from toughness and density.
Holding gemstones
Platinum is a favorite setting metal for diamonds and other fine stones for a few practical reasons:
- Platinum prongs bend and deform without snapping when hit, so a knock is less likely to break a prong and release the stone.
- The metal wears slowly, so prongs and bezels keep their mass for longer between repairs.
- Its white color does not reflect a yellow tint into colorless diamonds.
These qualities made platinum the dominant metal for fine diamond rings from the early twentieth century. The gemstone settings page explains prong, bezel and other setting styles.
Allergies and skin
Platinum jewelry at 95 percent purity rarely causes skin reactions. The common alloy metals (iridium, ruthenium) are also unlikely irritants. That makes platinum a common recommendation for people with a nickel allergy. If you are very sensitive, ask whether a piece uses a cobalt or copper alloy.
History of platinum in jewelry
Pre-Columbian goldsmiths
The first people known to work platinum lived on the Pacific coast of present-day Ecuador and Colombia, in the region around La Tolita and Esmeraldas, roughly two thousand years ago. Their goldsmiths could not melt platinum. They mixed fine grains of platinum with gold dust and heated the mixture until the gold melted and bound the platinum grains together, a form of sintering. Repeated hammering and heating produced a workable metal. Small ornaments and nose rings made this way survive in museum collections. The pre-Columbian jewelry page covers their gold work.
European discovery
Spanish colonists in South America found grains of a whitish metal in gold placer deposits of the Choco region of present-day Colombia. They called it platina, "little silver," and treated it as a nuisance that spoiled gold. European scientists studied samples in the eighteenth century and concluded it was a new metal. Antonio de Ulloa published an early description in 1748.
Working platinum remained hard because of its melting point. In the early nineteenth century, William Hyde Wollaston developed a powder method that produced malleable platinum, and later in the century the oxy-hydrogen torch made melting practical. Platinum deposits in the Ural Mountains, found in the 1820s, gave Russia a new supply, and the Russian treasury struck platinum coins from 1828 to 1845. Large deposits in South Africa's Bushveld Complex, identified in the 1920s, became the world's main source.
Edwardian and Art Deco jewelry
Jewelers in Paris and London adopted platinum around 1900. Its strength let them make very thin, lace-like settings that held diamonds with almost no visible metal, the style now called Edwardian or garland style. Cartier and other houses made it fashionable.
In the 1920s and 1930s, platinum became the defining metal of Art Deco jewelry, with geometric designs, calibre-cut colored stones and white diamond pieces. During World War II, the United States and other governments restricted platinum for military uses, and jewelers turned to white gold. Platinum returned to wide jewelry use after the war.
Cost and buying notes
Platinum jewelry usually costs more than gold jewelry of the same design. Part of that comes from the metal price, part from the higher purity (95 percent versus 58.5 or 75 percent for gold) and part from the weight, since the same ring uses more metal by mass. Working platinum also takes special tools and more skill, which adds labor cost.
When buying, look for the purity mark inside the band. Ask about the alloy if you have allergies, and ask whether the shop polishes platinum on resale or repair. Palladium, a related metal, offers a similar white color at lower weight.
Frequently asked questions
Is platinum stronger than gold?
Platinum is denser and tougher, so prongs bend instead of breaking and metal is rarely lost to wear. It still scratches, often a little more visibly than 14K gold, and develops a patina over time.
Does platinum need rhodium plating?
No. Platinum is naturally white. Some jewelers plate new platinum for extra brightness, but the plating is optional and the metal underneath stays white.
What does PT950 mean?
It means the item is 95 percent platinum. The other 5 percent is an alloy metal, usually iridium, ruthenium or cobalt.
Why is platinum jewelry heavier than gold?
Platinum has a density of about 21.45 g/cm³, compared with roughly 13 to 16 g/cm³ for 14K and 18K gold alloys. The same design uses more metal by weight.