How do you separate clear diamonds and clear plastic imitations?

One way to separate clear diamonds from clear plastic imitations is by examining their hardness. Diamonds are one of the hardest natural materials, so they can scratch glass or plastic imitations. Another way is to check for the gem's refractive index, as diamonds have a higher refractive index compared to plastics. Lastly, you can also use a loupe or magnifier to look for natural inclusions or imperfections that indicate a real diamond.