Over time, your jewelry will acquire a patina, which is completely normal. The patina (gold or silver layer) tends to fade gradually.
The speed of this alteration depends on the material and maintenance of the jewelry.
Jewelry naturally oxidizes with air and humidity.
I recommend that you clean them regularly by rubbing them with a soft, dry cloth and store them in a closed bag or box away from light.
Using a soft brush, I recommend that you clean your jewelry from time to time in cold, slightly soapy water (Marseille soap, for example) to remove any deposits, then rinse them with clean water and dry them carefully with a dry cloth.
When silver jewelry is too oxidized, has not been maintained, worn or protected, it turns black.
You can clean them in a special deoxidizing bath or entrust them to me at the workshop for a complete cleaning. Service charged.