18k indicates that the purity of gold in jewelry is 18K. 18K is not weight, but proportion. Theoretically, the gold content of 100% is 24K. In fact, gold with a purity of 100% is impossible. Our country stipulates that gold with a purity of over 99.9% is 24K. 18K means that the proportion of gold is 18, 18/24=0.75, that is, 750 thousandths. Therefore, the gold of 18K is marked with the words AU750, 18K or G750.

825 silver 5 yuan is about one gram, and the silver content is 82.5%. Silver can be inlaid with diamonds.