Diamond stimulants like CZ may be suitable for costume jewelry, and the average person in casual circumstances may not know the difference between a CZ and a natural diamond. However, no professional will be fooled and laymen who would like to know the difference between diamond and CZ can try these fun and easy tests:The Huff Test
Hold the stone in question next to a diamond and "huff" on them with your hot breath. Both stones will fog up. The diamond will clear up rapidly, while a CZ will take a little longer. This is due to diamond's greater thermal conductivity.
The Flash Test
When a CZ is upside down and backlit (light coming through the crown, viewed from the pavilion side) its pavilion facets will often "flash" orange.
The Weight Test
CZ is 80% heavier than diamond. Hint: This will show up pretty fast when she's comparing items with her friends.
The RI Water Test
Put the CZ a glass of water, along with a diamond. A CZ (with a 2.2 refractive index versus diamond's 2.42) will appear more "transparent" than a diamond. It will look more "washed out", or "ghostlike" compared to a diamond.
The Dispersion Water Test
In a dark room, put the stone in question in the bottom of a glass alongside a diamond, face down. Lift the glass up a couple inches, and shine a flashlight down on them vertically from above. Diamond has a dispersion of 0.44, while CZ's is 0.66, 50% more. You will see a circular pattern of light images under the stones which has been "stretched out" into a rainbow spectrum. If one of the stones is a CZ, its rainbow spectrum will be 50% longer, more "stretched out" than a diamond. The difference in look is obvious.
The Give It As An Engagement Ring Test
Give the stone in question to your fiancée as an engagement ring. If she throws it back in your face within 24 hours, it is a CZ. This is the most decisive test of all of them.
Provided by Whiteflash