Like many metals, bronze and sterling silver tarnish by nature. The best way to prevent tarnish is to wear your piece often! Should tarnish occur, a polishing cloth such as Sunshine brand is recommended. Silver dipping solutions are great for cleaning silver chain, but please don't dip any pieces featuring a black patina. Never use a dipping solution or polish for metals other than those specified on the product. If your piece features a black patina to enhance details, please take extra care not to wear while showering or cleaning house. Regular hand-washing is harmless.
If you have any questions, don't hesitate to ask!