If you enjoy collecting antiques or found artefacts and restoring them, you may be interested in learning to identify old brass. Before you can determine whether the lamp or piece of hardware you want to restore is made of aged brass, however, you need to be aware of some of brass's properties. Brass comes in many different alloys, each with a different specific composition of metals, but is usually made of mostly copper and some zinc, although older brass alloys may also contain lead.
Check the object for encrustations resulting from the oxidation of the metal. Because brass is a cupreous metal---an alloy of copper---aged brass may resemble aged copper, with a greenish or bluish patina forming on exposed surfaces.
Remove encrustations by soaking the metal object in a solution of 5 to 10 per cent citric acid. Leave the object submerged in the solution for anywhere from an hour to several days, until the encrustations have dissolved or fallen off and you are better able to identify the metal underneath. Stir the solution periodically to prevent acid build-up and metal corrosion.
Remove the finish with a brass stripping product if the object has a polished finish that has changed the metal's colour. The properties of brass can result in a metal that is varying shades of brown, pink or yellow, but most aged brass and many polished brass pieces have a tendency to yellow.
Lightly buff the metal surface with steel wool to remove any remaining debris covering the colour of the metal. When you have removed all encrustations, finishes and debris, you can distinguish brass from copper by the yellow (rather than pink) colour tones. The properties of brass also result in a stronger metal than copper, which is very malleable.
Check for magnetism. If the metal attracts magnets, it contains iron and may have brass plating, but the object cannot be solid brass.
Test a small area of the metal to distinguish aged brass from bronze, which is a very similar alloy. Brass will turn pink when tested with hydrochloric acid and will come to resemble pure copper as acid removes the zinc. Because this is a corrosive test, use the acid sparingly and only on a small area of the metal.
Use caution when treating metals with any form of acid, which can damage the skin and other objects. Always wear rubber gloves when working with acid, and thoroughly clean up the area in which acid was used.