The finger of the diamond gold ring is black before it is dark. There is a national inspection certificate bought by the mall

The finger black should be that the gold -plated layer on the ring is worn out. The gold is 750 per thousand, and the inside contains other metal elements.
So wearing fingers did not get black before. Recently, it was black because the surface coating was worn. You can find the jewelry factory from the new plating.

The hand is black or the ring is black