The calculation method of the fineness of K gold is: fineness = K ×4. 15% (gold content per k), and 900 is the expression method with three digits between 2 1K and 22K (indicating that the gold content is 900‰, which is equivalent to 18K gold).
According to the Regulation and Naming Method of Precious Metal Purity of Jewelry (national standard GB/T1KLOC-0/887—2002), the minimum purity of pure gold is 990, that is, the purity is not less than 990 ‰; The minimum purity of pure gold is 999, that is, the purity is not less than 999‰, and gold 900 is not pure gold.
Extended data:
By May of 20 16, the printing of thousands of gold characters had been cancelled by the government. If the gold content reaches 999‰, it can be marked as "pure gold 999". Gold 900 is "AU900" with a gold content of 900‰, and the difference between the two is 99‰, which is definitely 900 cheap.
The difference between 900 and 999 lies in the different gold content, different uses and different prices.
Pure gold 999 jewelry: it is original pure gold, which is widely used in gold bracelets, necklaces, rings and other gold jewelry. Both style and gold content are popular favorites.
AU900: Jewelry with 900‰ pure gold content hardly exists. 900 is mainly used for stud earrings of gold earrings and fixing buckles of open bracelets, and is an accessory for fixing jewelry. Because gold jewelry is soft, the earrings of gold earrings can't be made of pure gold, and the hardness can't reach.
Therefore, when our consumers exchange gold earrings for new ones or sell them, they all cut them out and weigh them separately. If it is the same brand, it will not be deducted by default.
Baidu Encyclopedia-Rules and Naming Methods of Precious Metal Purity in Jewelry