How to tell if a diamond is real - in this scenario?

Here are some ways to tell if it were a fake diamond: fake will shine, but shines rainbow reflections, real diamonds have a gray or blue shine to them. Real diamonds disperse heat quickly...if you were to blow hot breath on a diamond it will only fog up for a second, a fake will stay foggy for a while. With a fake, you can use it like a magnifying gl, looking through and able to see writing (for example) easily. With a real diamond you could not at all because it does not refract as much light. This also means if you were to shine a light into the real diamond, you would not see it on the other side, you could with the fake though. Hope this helps. You could use these ways and branch off greatly. An idea for your story might be something like... "the girl lifts her necklace up to her face...she looks through, able to see right through the diamond deception...and able to see his deceptive face..." Good Luck :) Leanna