Authentic sterling silver items should have a stamp saying "STERLING SILVER" or "925". Other stamps can be "SW", "MEXICO", and "ITALY".
You can use a mild your bath soap to clean sterling silver accessories. You can also use metal polish to clean your sterling silver accessories. Silverworks even has a special cleaner that you can buy from any store. A good tip to prevent tarnish is to wear your sterling silver accessories more often. Our body oils can actually lessen tarnishing.
One of the most important things to remember in caring for your sterling silver accessories is proper storage. Leaving your sterling silver accessories in open-air and humid areas can make them tarnish quickly. Instead, put them in air-tight bags to avoid tarnish and scratches. Keep in mind also that wood containers are not advisable because wood acids can make silver deteriorate. Always store your silver separate from each other to prevent scratches. Never crowd them in one box.
Silver tarnishes and becomes black in color because of sulfur compounds in the air. All silver tarnishes. This is why Silverworks provides free cleaning for all Silverworks bought items, we want your jewelry clean shiny all the time.