I've recently bought a princess cut diamond ring set in platinum. The diamond shows a slight yellow colour and no inclusions I can see under a microscope. I only started to doubt myself when I tried the fog test. Any ideas please, I'm losing sleep over this!
Get a professional appraisal done as soon as possible. The fog test is not reliable. Some fakes clear up immediately, some diamonds stay foggy for a few seconds. You need to speak with a professional with proper equipment.
I agree with all of the above. Telling if it's a real diamond is easy, it's usually free, and it's a good idea to get this question out of your mind quickly. Today would be good. Pretty much any jewelry store or pawn shop can tell you in a matter of seconds. The exact details and what it's 'worth' is a significantly harder question and for that you would benefit by getting a professional apraisal. As a side benefit, the appraisers report is usually a requirement for securing insurance.
Totally agree with the others. The fog test isn't reliable as JG said, the stone has to be very clean and even then it's not fool proof. Don't panic yet! Keep us posted!