Gift Idea: Birthday gifts for her, Valentines day gifts for girlfriend, Christmas gifts, wedding anniversary gifts for wife, mom birthday gifts, 21st birthday gifts for her, gifts for mom, engagement gifts and bridesmaid gifts, Attributes of 925 Sterling Silver Hallmark. If your item contains a S925 hallmark, it is sterling silver. Oxidization. When silver is exposed to air, it oxidizes. The oxidization of the silver causes the metal to tarnish and take on a black tint over time. If you see black tone after a period of use, the item is sterling silver. Magnetic. Like gold and platinum, silver is a non-ferrous metal,it is not magnetic. Run a strong magnet over your item. If the item is not attracted to the magnet, it is made out of a non-ferrous metal. Caring for Sterling Silver Jewelry Keep the silver away from substances that will cause tarnish. Anything that contains sulfur will cause silver to tarnish. To prevent this from happening, keep your silver away from things like:Sweat,Rubber and latex,Food items like mayonnaise, mustard, eggs, and onions,Wool,Lotions, creams, and beauty products Take your jewelry off. Since there are so many things that can tarnish silver, it's a good idea to remove your jewelry when you go swimming in chlorinated water or do household chores (to keep the silver away from the chemicals). Wipe your jewelry clean with a silver polishing cloth before putting it into storage. Store it somewhere cool, dark, and dry. Humidity causes jewelry to tarnish faster, so the more you limit the humidity, the slower your jewelry will tarnish.