Whether you are buying a diamond new from a jeweler or used from a pawn shop, it is always wise to know the telltale signs of a fake diamond. While a professional will have the definitive opinion as to whether a diamond is authentic or not, there are ways to detect a fake. Fake diamonds differ from genuine diamonds in many ways. An ultraviolet light, also known as a black light, will reflect differently in most diamonds, thereby making it a useful tool in detecting fake diamonds. Buying a diamond is a large investment, one that may even be handed down through your family. You'll want to be sure that you're getting the real thing.
Hold the diamond in question under a long wave UV light (also called a black light). If the diamond reflects a blue fluorescence, it is most likely authentic.
Be aware that while the majority of diamonds on the market will have a blue glow under UV light, high quality diamonds will not. The UV light method should be performed along with other tests to detect a fake diamond.
Know that cubic zirconia will glow mustard yellow under a UV light. Glass will have no glow at all.
Familiarize yourself with the other methods of detecting fake diamonds, such as the reflection colors within the stone, the weight, the quality of the setting and the wear and tear on the stone itself.
Know that the final word on detecting a fake diamond is a professional appraisal. A certified and experienced gemologist will have the knowledge and skills needed to determine without a doubt that the diamond in question is authentic or a fake.