How to differentiate diamonds?

Finding out whether or not your diamond is real is a tantalizing proposition — do you want to know without a doubt? Most curious citizens turn to a professional jeweler in order to suss it out. But you don't have to be Sherlock Holmes to tell the real from the duds. A little bit of light, some water or warm breath, and a jeweler's loupe is all you need.

Testing mounted diamonds.

1. Use the fog test. Put the stone in front of your mouth and fog it like you would a mirror. If it stays fogged for a couple seconds, it’s probably a fake — a real diamond disperses the heat from your breath instantaneously and won't fog up easily. Even if you wait in between fogging it up and looking at it, it will still clear much faster than a fake.

2. Check the setting and mount. A real diamond is not likely to be set in a cheap metal. Stamps inside the setting indicating real gold or platinum (10K, 14K, 18K, 585, 750, 900, 950, PT, Plat) are a good sign, while a "C.Z." stamp will give away that the center stone is not a real diamond. C.Z. stands for Cubic Zirconia, which is a kind of synthetic diamond.

Use a jeweler's loupe to inspect the diamond. You can usually borrow one from the jewelry store. Mined diamonds usually have small naturally occurring imperfections, which are called "inclusions," that can be seen with a loupe. Look for small flecks of minerals, or very slight color changes. These are both signs that you're dealing with a real, albeit imperfect, diamond.