When testing for imitation or fake diamonds, the rainbow test involves looking at the diamond under a light and noticing how intense rainbow color flashes occur.

This test should be done with a real diamond for comparison purposes. If the diamond in question flashes rainbow colors much more than the "real" diamond, it may be an imitation.

It may be hard for the untrained eye to see the difference however.

Don't care if it's fake? Modern-day fake diamonds such as cubic zirconia (CZ) or moissanite are hard to tell from the real thing and can offer good value. Check out the links below if you're interested in buying fake diamonds: