Platinum is the natural choice for milestone jewellery, such as engagement rings and wedding bands, because it holds significant gemstones better than any other precious metal. Platinum is extremely durable, so there’s a minimal chance that prongs made from platinum will dislodge your diamond. Diamonds set in platinum are also enhanced by the natural whiteness of the metal, whose glowing patina gets more beautiful with time. And unlike white gold, which retains its whiteness only by being plated with rhodium, platinum will never need re-plating.
Platinum’s purity also means that it is naturally hypoallergenic. Recognised as an element in the 18th century, scientists soon discovered that this unusual white metal, difficult to melt using traditional methods, was also nearly incorruptible by gases or chemicals making it thoroughly non-corrosive. Platinum is also extremely dense. One cubic foot of platinum weighs in at “a little more than 1,330 pounds,” according to precious metals investor I. M. Vronsky, making it 11% heavier than gold. This density has made it a favourite among those who appreciate the feel of a weightier piece of jewellery.
When compared with the gold alloys commonly used in jewellery, platinum contains a higher concentration of its elemental metal. Pure gold is known as 24K, but is much too soft and malleable to be worn in most jewellery, so it must be alloyed with other metals. White or yellow 14K gold contains only 58.5% of the actual metal and 18K contains 75%. Naturally durable yet malleable, platinum need only be mixed with the smallest amount of other platinum group metals to create an alloy that can be moulded, cast and shaped into the world’s most elegant jewellery. Platinum jewellery is either 90% or 95% pure platinum.
Look inside a piece of platinum jewellery and you’ll see its purity stamp. The Federal Trade Commission demands specific marks for the content of any precious metal alloy. To protect American consumers, a high-content platinum alloy will be marked 950Pt, 950, plat or platinum, meaning that it’s at least 95% pure, elemental platinum. It’s also the only platinum alloy that can simply bear the “Platinum” stamp to identify that it’s 95% pure platinum. Other common metals that comprise the remaining 5% are iridium, ruthenium or cobalt. Another platinum alloy that’s popular in the United States contains 900 parts platinum to 100 parts other metals. The stamp for this particular alloy, per FTC guidelines, is 900Pt. In the United States, a brand’s registered hallmark must also accompany the purity stamp.