You know a diamond is real when it comes with GIA certification. However, what if the stone does not come with a GIA grading report? In this case, you would need other ways to tell whether it is authentic or fake.
The Fog Test
Place the gemstone in front of the mouth and try fogging it up with breath. If the stone remains fogged for just a few seconds, it is probably a fake one. A real diamond will not fog up easily because the condensation does not stick to its surface.
The Water Test
This one is easy to do. Fill a glass with any kind of water, and drop your diamond into that glass. Because of its high density, when dropped into it, a diamond will sink. However, if it floats to the middle or top of the glass, then it is a giveaway sign that it is not real.
Test with Magnifying Glass
To find out whether a diamond is real or not, use a magnifying glass and look at the stone through it. Look for flaws inside the stone. If you are not able to find any imperfections in it, then it is most likely to be a fake product. Real diamonds have inclusions.
With Black Light
Just switch off the lights in your room and hold the rock in front of UV light. Most diamonds will fluoresce blue under UV light; therefore, you will see medium-to-strong blue color, meaning it is a real diamond. If you see a slightly yellow, gray or green fluorescence instead of the blue one, this usually suggests it is not real. However, keep in mind that not all diamonds reveal blue fluorescence.
Jewelers and gemologists use a loupe to see tiny details up close. The lens frame of a loupe is a bit more conical than that of a magnifying glass, and there is no attached handle on the former unlike on the latter.
When you look through your loupe, look for internal flaws. Mined diamonds often have small, natural inclusions that suggest it is real. Then, check to see whether there are slight color changes or tiny flecks of minerals. If there are any signs of these, then it is most likely a real diamond. Most diamonds have inclusions, but avoid relying on this test alone as your full and final determination. Lab-produced diamonds usually do not have imperfections as these are made in controlled environments.