What does 1/2012k gf mean on a vintage broach/pin?

Answer 1

1/20 12K gf means that the broach is gold-filled (gf) which means that a thick layer of karat gold is applied to a base metal. The 1/20 is the proportional weight of the gold to the full weight of the broach and the 12k means that it is 12 karat gold.