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 99.6% 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.

75% of the precious metals in 18K are gold and 25% are other metals. Pure gold is very soft, and it is not suitable for jewelry modeling or gem setting. 18K gold added with other metals not only has the same valuable value as gold, but also has the advantages of strong ductility, high hardness and changeable color due to its perfect composition ratio. When used in jewelry design, it is not only colorful, but also three-dimensional, which can give full play to complex and exquisite creative expression and realize various shapes. Therefore, 18K gold is widely used in contemporary jewelry.