Various Tests That Can Be Conducted
Test 1: Request for a grading certificate. Any one of the following should be acceptable (i.e. PGGL, LGP, GIA or AGSL). Usually, the dealer of the diamond should also be affiliated with a professional organization and have official certification to verify this. It is crucial that you always request to see this certification when purchasing diamonds (especially via the internet).
Test 2: Test their refractive nature. True diamonds are highly refractive, i.e. they bend the light that passes through them. If you shine a light (such as the red beam light found in toys that have become common amidst the younger generation) through the diamond, it should bend the light quite significantly from its initial trajectory. Be cautious for double refraction however. If, when shining your light and viewing the diamond from the top, you notice something that looks almost like double vision, your diamond could be fake. A cleverly designed compound of silicon carbide may fool even the most experienced of jewelers.
Test 3: Look at your diamond carefully. If the diamond is mounted on a ring, bracelet, earring, etc., and you look at it from the top; you should not be able to see the bottom. If the diamond is not mounted, place it on its side on top of a paper with writing on. If you can view the writing through the diamond you are allowed to be a bit skeptical. However, if the diamond is disproportionately cut, this test may prove fruitless. You may very well be able to view the writing through an authentic, disproportionately cut diamond.
Test 4: Look out for tell tale signs. It’s common that genuine diamonds are mounted on fairly authentic jewelry. It’s not often you find a really expensive diamond mounted on cheap gold or platinum. Look for stamps within the mounting such as 10K, 18K, 750, 900, 950 etc. The initials C Z (i.e. Cubic Zirconium), is a total giveaway.
Look at the color of the diamond. Authentic diamonds have a slight yellowish tint to them. If the diamond is completely clear, chances are it's fake. The yellowish tint on the diamond makes gold mounting complimentary to the diamond’s inherent color and more attractive.
Test 5: Breathe on the diamond. Although this may not be viewed too favorably from the seller’s point of view, you’d rather be safe than sorry. Diamonds are exceptionally good conductors of heat. If, after 4 seconds after you breathe on the diamond, the diamond remains misted, it’s probably fake. With this being said, there are certain capped cupid zirconiums that will past this test. For the more veteran or cautious diamond purchaser, the purchase of a diamond/ moissanite tester would probably be quite a lucrative investment.
Test 6: Cost. The price of the diamond is largely quite a good indicator as to whether the diamond is fake or not. If a particularly large diamond is comparatively cheaper than what you may have conventionally expected, you should be a bit skeptical.
Test 7: Saliva. Although this may not be the most practical of tests, it has proven true from a number of diamond merchants. If you gather a bit of saliva on your forefinger and trail your finger around the surface of the diamond, your saliva should closely follow the trail you create with your finger. Saliva generally dissipates on other clear surfaces such as glass.