Moreover, with the accuracy of the existing instruments, even if the purity of gold jewelry does reach 99.99%, the general testing institutions can't detect it.
Extended data:
According to the definition of national standard, gold is divided into the following categories, and the minimum purity per thousand is 375, 585, 750, 9 16, 990 and 999 respectively. Other expressions of the corresponding purity are: 9K, 14K, 18K, 22K, pure gold, and pure gold. For jewelry, the national standard only defines thousands of gold.
A classification of gold purity is as follows: three 9s are 99.95%, four 9s are 99.99%, and 999 is 99.9%, which is18k; ; 9999 represents the purity of 99.99%, that is, 24K, and 999 represents the purity of gold, that is, thousands of pure gold, with the purity of 99.9%.
The latter 9999, commonly known as Wanjinjin, is not much higher in purity than Qianjinjin, and has little practical significance. It's just some tricks used by some businesses to improve their performance and slightly raise their prices. Gold 999 is 99.9% gold, and the latter is 99.99% gold. Thousands of pure gold is 99.99% gold and 99.9% gold.