When testing for imitation or fake diamonds, the girdle test involves using a 10X power magnifier, or loupe, to examine the narrow band around the edge of the diamond (called the girdle). Most natural diamond have slight defects in the girdle. Simulated diamonds will have a perfectly formed or faceted girdle.

Another way to tell is to look at the shape of the defects in the girdle. Real diamonds will have angular, sharp looking defects. Fake diamonds will have rounded-looking defects on the girdle.

This difference may be difficult to discern by the untrained eye 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: