You might wonder why anyone would be concerned with the difference between solid brass keys and brass plated ones. But antique stores and collectors of these items attribute value to solid brass. Furthermore, a very practical advantage of having solid brass keys is that they will never rust.
Brass is created by combining two metals--zinc and copper--to make an alloy. Brass is a versatile material that can be wrought, forged, cast or spun. It is used for home-decorating purposes--such as being employed in lighting fixtures and candleholders--or for very practical items like locks and keys. A clear lacquer coating is usually applied to brass to protect it from becoming oxidized.
Head for the toolbox or your child's collection of school supplies and take out a magnet. A refrigerator magnet will also work. Any hardware store or home-improvement store will have magnets.
Dangle your keys next to the magnet. If they are pulled in the direction of the magnet, they have failed the test. Solid brass will not be pulled by magnetic force, because it contains no lead or steel. Steel keys with brass plating, however, will respond to the magnet test.
Convince yourself further by scratching a tiny spot on the key with a sharp metal tool. If it leaves a yellow scratch, your key is probably brass. If it leaves a shiny silvery scratch, your key has been brass-plated. The core metal of your key is probably iron, steel or white metal.