How to Check a Diamond for Authenticity

Hold the diamond and gently blow on the stone. Because real diamonds disperse heat quickly, you should not see any fog on a real diamond. If you notice fog from your breath, you most likely have a fake diamond.

Place your diamond under a black light. If you see a blue florescence on the stone, then it is probably a real diamond, though it may not be a very valuable diamond. Conversely, if you don't see a blue florescence it doesn't necessarily mean that the diamond is fake; it could also mean that the diamond is of exceptional quality and value.

Examine the transparency of the diamond by putting the stone onto a piece of paper with printed words. If you can read the words through the diamond, then the diamond is fake.

Check jewelry stamps if your diamond is set into a piece of jewelry such as a ring, bracelet or necklace. Stamps that identify real gold and plantinum, such as markings like 10K, 14K, 750, 950, PT or Plat are more likely to hold a real diamond. Stamps such as 925, which stands for silver, or GE, which stands for gold electroplate, are less likely to hold a real diamond. A CZ marking indicates cubic zirconium, rather than a diamond.

Look for markings on the stone with a magnifying lens. Note whether the cuts on the top of the stone have sharp points. These sharper cuts may indicate a real diamond. If you notice little cracks, carbon or pinpoints, these may also be indications the diamond is real.