Au750 refers to gold with a gold content of 75%, and 12 is the ring number of the ring. If pure gold is 24K, 75% of it is 18K, so au750 is also called 18K gold. Au is the symbol of the chemical element of gold, and the content of 750 refers to 750 thousandths, pure gold is 24K, and 750 thousandths of 24K is 18K. Many rings and pendants will be engraved with AU750, which is 18k gold, containing 75% gold. So the symbol marked 750, regardless of the previous symbols, is 18K, 18 divided by 24 equals 75%, and 24k gold is pure gold.

The gold content of 18K gold is the general specification of jewelry, and the state stipulates that gold jewelry below 9K cannot be called gold jewelry. Some gold ornaments are marked with words, which stipulate that pure gold-the gold content is not less than 99%, and thousands of gold-the gold content is more than 99.9%. China has regulations on the imprint and identification card of gold products, generally requiring the manufacturer's code, material name, content imprint, etc. Products without marks are unqualified.

Extended data:

The gold ring represents the purity of gold with "K gold": in theory, we call the gold with 100% as 24K；; Therefore, the calculation method is 100/24: according to national regulations, the gold content per k is 4. 16666%, so gold ornaments are generally divided into 9K, 14K, 18K and 24K. Their gold content is as follows:

9k = 100/24 * 9 = 37.5%；

14k =100/24 *14 = 58.333% (585 ‰), which is set to 58.5% for easy identification;

18k = 100/24 * 18 = 75%(750‰)；

22k =100/24 * 22 = 91.666% (916 ‰), which is set to 9 1.6% for easy identification.

In theory, 100% gold can be called 24K gold, but in reality it is impossible to have 100% gold, so China stipulates that gold with a content of more than 99.6% (including 99.6%) can be called 24K gold. 24K is the color code of gold products. 24k gold is often considered as pure gold, but the actual gold content is 99.998%.

Baidu encyclopedia -au 750