Firstly, a real diamond has a completely different and much more intense reflection of light, which makes it very different from artificial stones. To check a diamond that is already set, you have two simple, though not perfect, ways to test it. First possibility: the fog test and the checking of the setting. In the fog test, the stone is breathed on and if it remains fogged, it is probably a fake. Genuine diamonds repel heat and clear up immediately. The other option is to look inside the setting. Whenever you find a stamp with the inscription "C.Z"...', this indicates that the set stone is a synthetic stone, the so-called "Cubic Zirconia". Further, jewelry can also be tested by a jeweler. We recommend this in case of doubt, as the above-mentioned methods are not flawless.