Read the stamp
What does 1/20 12K GF mean on jewelry
1/20 12K GF means a 12-karat gold-alloy layer makes up one twentieth of the article’s metal weight. GF describes the bonded construction.
What each part contributes
1/20 is 5% by weight of gold alloy, and 12K is 50% gold within that layer. Multiplying the two gives 2.5% fine gold by metal weight. GF describes the bonded construction. This is different from an object made throughout of 12K alloy.
What to check next
Compare GF and RGP, which describe mechanically applied layers, with GP and HGE, which describe plating. Look at the entire coating stamp before interpreting a karat number. At worn edges the base metal may be visible; a maker signature beside the construction mark identifies the company.