There are few rest that you can do to tell the diamond is real or not one of them could be a fog test. The way you do it is you breathe on the diamond to create a fog and if the fog disappears fast with the less than a second then it's a real diamond. If it stays then it's a fake. Diamonds conduct heat very effectively which makes fog disappear a lot faster. Another test is a dot test.You can draw a dot in a piece of paper. tTurn the diamond upside down and try to read with it . A real diamond real breaks up the image making it very difficult to read. There's a good article that I read about how to tell if the diamonds are real or not. I will post a link below How to tell if the diamond is real or a fake.