England accepts 9k gold, while in some countries of the world, 8k is the legal minimum standard. Gold can be alloyed in a range of colors but only a few alloys have the right combination of strength, beauty and workability to qualify for use in jewelry. Most jewelry contains a mixture of at least two other metals. Green gold is achieved when silver, and sometimes small amounts of copper and zinc are used as alloys. A pink or red tint results when gold is alloyed with copper.
White gold is made by combining gold with copper, nickel and zinc.
Small amounts of alloy metals can make a noticeable difference in the color of these coins. The pure gold is noticeably yellow in comparison. Items must be marked gold filled preceded by the karat fineness of the plating. A term that some would reserve for fine or 24k gold because it contains no other metals. However, in 1967 the federal Trade Commission held that solid gold may be used to describe articles that do not have a hollow center and are 10k or finer.