Platinum is the rarest metal, making it considerably more expensive than even pure gold. Eighty-five tons of platinum are mined annually, compared to the 1,500 tons of gold. Ten tons of ore must be mined to produce just one ounce of platinum. It takes five months to refine platinum before it can be used in jewelry.
Platinum is the purest metal. Platinum is the only precious metal used in fine jewelry that can be 95% pure. Small amounts of iridium and ruthenium (a metal from the platinum family) are commonly added to platinum. The stamp will read PLAT, PT or 950. Platinum’s purity makes it the only truly hypoallergenic metal.
Platinum is also the strongest metal. It weighs 60% more than gold and has a high resistance to heat. It is very dense and extremely resistant to wear. Although platinum will still scratch just like any precious metal, the scratches do not represent material loss.
Although gold is not nearly as rare as platinum, it is equally as desirable. Gold does not rust, tarnish or corrode. It takes 17 tons of gold to ore to extract one ounce of pure gold. It then takes three weeks to refine the metal to be used in jewelry.
In its purest form, gold is too soft to withstand the wear and tear of everyday use. So, alloys are added to make gold more durable. Pure gold is 24 Karat, or twenty-four parts gold. It will be stamped 999. 14 Karat gold is 14 parts gold and 10 parts of another alloy (usually silver, zinc or nickel), or 58% pure gold. The stamp will read 14K or 585. 18 Karat gold is 18 parts gold and six parts of another alloy, or 75% pure gold. The stamp will read 18k or 750.
Gold is naturally yellow, but you can find it in white, rose and green. Different colors are achieved by adding different alloys. For example, white gold is made by adding nickel and zinc and rose gold is made by adding copper. Adding silver gives gold a slight greenish tint.
Sterling silver is the third precious metal. It is frequently used in jewelry because it is relatively inexpensive, it is an abundant metal and it is easy to form. Silver is half the weight of platinum and is alloyed with 7.5% copper. Its stamp will read 925.