Platinum is a durable, hard, and dense metal that is very resistant to scratching. It is hypoallergenic and tarnish-resistant. Platinum is a beautiful metal, and diamonds show a lot of life when they are set in platinum. Platinum develops a patina and looks prettier with wear. Platinum jewelry is 90 to 95 percent platinum and is alloyed with other platinum group metals. Due to the higher purity of platinum in platinum jewelry (compared with the percentage of pure gold in most gold jewelry, for instance), platinum can be expensive. Platinum is the rarest of the three metals.