About the gold jewelry:
The fineness of a precious metal object represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardness and durability of jewelry, alter colors.
Karats measure the parts per 24, so that
18 karat = 18:24 = 75% (18K Stamp: Au750 / G18k)
14 karat = 14:24 = 58.5% (14K Stamp: Au585 / G14k)
10 Karat = 10:24 = 41.6% (10K Stamp: Au416 / G10k)
9 Karat = 10:24 = 37.5% (9K Stamp: Au375 / G9k)