VIKI LYNN Dog Necklace 925 Sterling Silver Puppy Beagle Gifts for Dog Lovers GIFT IDEAS/b> Christmas Gifts, gifts for teenage girls, 21st birthday gifts for her, graduation gifts, niece gifts, best friends gifts, cousin gifts, wedding anniversary gifts for wife, cute gifts, gifts for girlfriend, dog memorial gifts and dog gifts for dog lovers. 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 jewellery 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, Wool, Lotions, creams, and beauty products. Wipe your jewellery clean with a silver polishing cloth before putting it into storage. Store it somewhere cool, dark, and dry. Humidity causes jewellery to tarnish faster, so the more you limit the humidity, the slower your jewellery will tarnish.