An alloy of platinum with various other metals, e.g. palladium, copper, rhodium, iridium, osmium, etc. Platinum to be used in jewelry must be made workable by being alloyed. Since 1 January 1975 platinum has required a legal hallmark in Great Britain. The usual proportion of platinum in alloy used for jewelry is 95%.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson