Black light test: When you place a real diamond underneath an ultraviolet light, the stone with fluorescence in it will turn blue. But it's important to know that this will only happen with about one-third of all diamonds. A fake diamond, on the other hand, will almost never look blue under a black or UV light.
The phenomenon that causes a diamond to glow under black light is called fluorescence. Around 35% of diamonds grown naturally have this component in them, and 95% of them glow a bluish color when exposed to a black light.
Ultraviolet Light: About 30% of diamonds will glow blue under ultraviolet lights such as black light. Fake diamonds, on the other hand, will glow other colors or not at all.
Diamonds glow in black lighting due to a phenomenon called fluorescence and roughly 35% of natural diamonds exhibit some degree of this effect. In nature, the presence of certain chemical impurities within the diamond's composition triggers this glowing effect in the presence of an ultraviolet light source.
Usually fluorescence is blue in color. Less often, a diamond can have yellow or even white fluorescence (other colors too). Diamonds with Strong - or Very Strong - fluorescence can appear quite cloudy, milky or hazy to the naked eye, and emit a prominent and saturated glow in the presence of UV light.
Only about 25% to 35% of diamonds exhibit some degree of fluorescence in reaction to long-wave UV light. More than 95% of these diamonds fluoresce blue. A rare few fluoresce other colors such as yellow or green.
Sometimes, tiny amounts of impurities in diamonds can cause them to glow or luminesce under UV light. UV diamond fluorescence occurs in about 35% of colorless (white) diamonds and can be faint or very strong. (Fluorescence is a type of glow that occurs almost immediately after exposure to UV light).
Fake diamonds like cubic zirconia do not glow under black light!
Fluorescence is the visible light that a diamond emits when it is exposed to the UV rays. Fluorescence is naturally occurring, and at it's best it can make off white diamonds look whiter or more colourless. Around 30% of diamonds evaluated by the GIA have varying degrees of fluorescence detailed on the certificate.
The way that diamonds reflect light is unique: the inside of a real diamond should sparkle gray and white while the outside should reflect a rainbow of colors onto other surfaces. A fake diamond, on the other hand, will have rainbow colors that you can see inside the diamond as well.
Black light test:
When you place a real diamond underneath an ultraviolet light, the stone with fluorescence in it will turn blue. But it's important to know that this will only happen with about one-third of all diamonds. A fake diamond, on the other hand, will almost never look blue under a black or UV light.
A pure and natural diamond is known to produce a blue glow when exposed to black light. The impure ones have certain chemical impurities that trigger the glow of other colors like green, white, red, and yellow when diamonds are exposed to ultraviolet light.
Hold it in the light to see how it sparkles.
A fake diamond will have rainbow colors that you can see inside the diamond. “People have a misconception that diamonds sparkle like a rainbow, but they don't,” Hirsch said. “They do sparkle, but it's more of a gray color.
You will see that the diamond has white or silvery sparkles only. However, cubic zirconia will give out colourful sparkles such as red, yellow or blue. Another important differentiating feature between these two stones is that a diamond possesses sharp facets, whereas a zirconium does not have sharp facets.
You will see a glow in 30% of diamonds under UV light. 99% of the time, the glow is blue, but on rare occasions, diamonds glow white, yellow, green, or even red in color. Depending on the diamond, fluorescence can either improve the diamond's color or make it appear hazy or milky.
The most obvious difference between moissanite and diamonds is their brilliance, with moissanite possessing more brilliance than a diamond. “It has more fire and brilliance than any other gemstone, meaning it has more sparkle,” reveals O'Connell.
Water Test
Gently drop the diamond into the glass. If the diamond sinks to the bottom, it's real. If it floats at the surface or just underneath, it's likely a fake. This has to do with a diamond's high density.
You cannot spot a synthetic diamond by looking at it through a loupe. The only way to tell is by laboratory testing. Myth: A real diamond will have sharp edges, a “fake” diamond will not. Fact: This is only true for imitations that are made in a mold, like plastic (and some glass).
Using cold water is a much simpler and safer way to test the validity of a diamond. If you place the stone into water, a real diamond will sink to the bottom due to the density. Fake diamonds are far more likely to float or bobble around.
An ideal cut diamond shows only a few intensely bright flashes in direct sunlight. A diamond that actually looks good in sunlight splits those few flashes up into ten or twenty smaller sparkles.
Moissanite, being a lab-grown gemstone with a different chemical composition, has a unique luminescent behaviour under blacklight.
Cubic Zirconia (CZ) often shows orange fluorescence but in REVERSE ORDER. This reversal is a sure test for diamond versus CZ. vs.
Any diamond will flash, sparkle and look the best in direct sunlight. So, if you really want to know what exactly a diamond looks like, you must observe it in natural daylight. This is when its true brilliance and sparkle can be noticed.