In Germany the fineness of an alloy (i.e. the content of the most precious metal it contains) is always expressed in terms of parts per 1,000. For example, an alloy that is 75 percent pure gold is expressed as 750 parts per 1,000 (18 carat gold).
The white color of white gold was formerly created by adding nickel. After more and more cases of nickel allergy came to light, jewelrymakers switched from nickel to palladium, a chemical element in the platinum group.