The luster is still bright, but it is not as radiant as before. Although gold oxidizes slowly, it will oxidize after a long time and turn black after a long time. Oxidation is only a small part of the reason. The biggest reason is stained with dirty things. There is no denying that people will still have mud when they take a bath every day. So if the gold turns black, just wash it. If you don't want to go, you can wash it yourself. Dilute the detergent with water, soak the gold in it for half a day, and then wash it carefully, and it will be as bright as new.