Karat: Represents the number of parts out of 24
9K or 9C Used only in Britain and Colonies
10K Lowest allowed by law in the US that can still legally be called "gold."
14K Most commonly used standard in US today
15C Used in Britain.
18K or 18C Preferred by high-end designers. Stronger yellow color.
22K Used mostly in middle and far east. Strong yellow color. Very soft.
EUROPEAN MARKS: Number parts of 1000.
950 newest mark for platinum
5 irid plat 5 alloy with iridium
10 irid plat 10 alloy with iridium
925 925 parts of 1000 silver
800 called "800" silver, Continental
German silver or nickel silver - not silver at all.