10. Use a Loupe
A loupe is a small magnification device used by jewelers to examine small details up close.
Loupes don't have handles attached and the frame is conical.
You can purchase your own online.
Examine for inclusions, slight color changes, and flecks, which would indicate that the diamond is real.
Lab created diamonds are usually flawless, so if it doesn't have any imperfections, it's fake.
If you think you have a set of jewels that could be real, definitely go through this list of tests!
If they happen to be in a setting, the setting should be a quality metal- that's also an easy indicator of a quality stone.
But the best way to tell is having a professional evaluation!