Because silver sulfide is gray-black, with the intensification of the reaction, silver sulfide increases and thickens, and the surface color of silver gradually turns from white to yellow to gray, and finally turns black.
Extended data:
If it has been oxidized and blackened, you can use a soft brush dipped in toothpaste or a neutral detergent to clean it. If it is really impossible to clean, brush it with silver washing water and dry it with cotton cloth after washing.
Silver turns black not because of oxidation, but because it reacts with sulfur in the air to produce sulfide, which generally occurs in places where the concentration of hydrogen sulfide and other gases in the air is relatively high. Gold element is stable in nature, and this phenomenon generally does not occur.
References:
People's Network-The brighter the silver bracelet, the healthier it is. Is it true?/You don't say.