Brass is a metal alloy composed of zinc and copper. Changes in the quantities of zinc and copper in relation to each other will produce varying calibers of brass, and occasionally brass also will contain small parts -- less that five percent -- of other metals. More copper will give brass a yellower tone while more zinc will create a whiter tone. Brass can be used to make anything from coins and locks to expensive musical instruments. It is important to establish that an object is real brass before attempting to buy or sell it.
Examine the object that you have. Sometimes it may be as simple as looking at an object to test out whether it is real. Brass is usually yellow in color. If the metal isn't a tint between a bright white-yellow and a dull yellow similar to gold, you can rule it out. Also examine the item for signs of wear. Solid brass will tarnish, whereas brass plate will rust.
Place a magnet against the item. If the magnet sticks, then the item is either brass plated or composed of some other type of metal. Brass plate is a very thin sheet of brass placed over another, usually cheaper, metal. A magnet often will stick to brass plate because of an iron-based metal beneath it.
Scratch the surface of the item with a sharp knife. This should probably be your last resort as you don't want to ruin the object. If you feel you need to check in this manner, scratch the item in an unnoticeable place. The metal on the inside of the scratch should match the surface's brass color. If another color, like silver or black, shows through, the item is not solid brass.