Using a magnet, you can tell whether an item is solid brass or copper. Brass and copper are not magnetic, so the magnet will not stick. If the magnet sticks, then there is another base metal underneath. Silver pieces usually have a stamp on them indicating whether they are silverplate or not. Solid gold usually is stamped with the karat value of the solid gold. Many times you can just make an educated guess based on the amount you paid for the item.