Sterling silver is a metal used in the creation of jewelry, flatware and other common items. Because genuine silver is too soft to be used alone, it is typically mixed with other more durable metals, such as nickel and copper. For an item to qualify as real sterling silver, it must be at least .925 pure silver; only 0.075 may consist of non-silver metals. Sometimes an item may have an overlay of genuine silver on top of another metal. This is called silver plating and is not considered sterling silver. Silver plating can be worn away with use, revealing the lesser-quality metal underneath.
Identify real sterling silver is by its authenticating mark. When genuine silver is crafted, it is often engraved with a marking such as 9.25, Sterling, Sterling 925, or S/S. On jewelry, this marking is typically found on the clasp; on flatware, the marking is found on the underside of the utensil. Items without the sterling silver marking are rarely genuine silver.
Examine the item's coloring closely. Genuine silver is typically less shiny and cooler in tone than silver plate. If you see places where the silver appears to have worn away or flaked off, the item is probably not sterling silver.
Use a soft, light-colored cloth to rub the item. If the cloth shows black marks, the item is probably sterling silver. This is because real silver oxidizes and tarnishes when exposed to air, and the tarnish is rubbed off onto the cloth when polished.
Take the item to a jewelry store or pawn shop, and ask to have the item tested with nitric acid. This harsh industrial chemical will discolor non-silver materials because of their high copper content. Because the nitric acid will leave a permanent green spot on any silver-plated items, be sure to have the substance applied in a non-conspicuous spot.