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Pure Gold is 99.9% pure and is 24 Karat 916 Gold is 91.6% pure and is 22 Karat (24-22 = 2, 2/24 = 0.833, 1 - 0.833 = 91.666j%) The 8.33% impurity is usually Silver, Zinc Nickel or other metals. 22 Karat with copper is known as Crown Gold and is only used for UK Gold Coins and Soith African Krugerrands which 18 Karat Gold is 75% pure (24-18 = 6, 6/24 = 0.25, 1 - 0.25 = 0.75 or 75%) The 25% mainly being copper is most common Rose Gold (Rose Coloured, same thing) 14 Karat is 58% pure (24 - 14 = 10, 10/24 = 0.42 etc)