A real diamond appears gray and white inside (brilliance) when held to the light and can reflect rainbow colors (fire) onto other surfaces. A fake diamond will display rainbow colors within the stone when held up to light.
Hold it in the light to see how it sparkles.
“They do sparkle, but it's more of a gray color. If you see something with rainbow colors [inside the stone], it could be a sign that it's not a diamond.”
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.
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.
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.
This water test is easy if you have a loose diamond: Get a glass and fill it with water (it doesn't matter what type of water you use). Drop the diamond into the glass of water. Due to the high density of diamonds, when dropped into the water a real diamond will sink.
Water testing your diamond
Get a glass full of water and simply drop your diamond into the glass. If the diamond is real, it will drop to the bottom of the glass due to the high density of the stone. If it's a fake, it will float on the surface of the water.
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.
In cut stones, cubic zirconia tends to have dull, rounded edges, while diamonds' facets stay sharp. Diamonds rarely show polish marks, but if they do, they will be in different directions on different facets. On the other hand, cubic zirconia will show polishing marks in the same direction on adjoining facets.
Most diamonds will have a blue-colored glow, but if you see the slight green or yellow fluorescence instead, you'll need to seek the opinion of a professional jeweler as this may mean your stone is not genuine. Although this is not 100% sure, it would be best to have it checked by a reputable jeweler.
Sparkle Test
Pay close attention to the way your gem reflects the light. It's common for a diamond to demonstrate grayish and white sparkling from inside and scatter it in rainbow colors around. In its turn, fake stones tend to intensify rainbow-colored reflection, with no gray and white presence in its spectrum.
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.
As straightforward as it sounds, fill a glass of water at home to roughly three-quarters full. Separate the stone so that it is loose, and drop it into the water. Diamonds are highly dense and a genuine gem will sink to the bottom – every time. If it hovers to the surface or only partially sinks, then it is a replica.
Minerals are assigned a number between 1 and 10 on the Mohs Hardness Scale to describe how resistant to scratching they are. Diamonds are given the highest number, a 10. There is nothing that can scratch a diamond except another diamond. A mineral like talc, on the other hand, is a 1 on the scale.
Genuine diamonds do not sparkle in rainbow colors inside of the stone. Instead, the inside of real diamonds sparkles in tones white and gray. The play on light in the diamond is brilliance. One factor that determines a diamond's level of brilliance is the cut.
CARLSBAD, Calif. – Feb. 27, 2013 – Owners of Android phones and tablets like the Kindle Fire and Samsung Galaxy can now benefit from GIA's (Gemological Institute of America) free interactive diamond app for consumers and retailers, available in both English and Simplified Chinese.
True diamonds have high density and should quickly sink to the bottom of the glass. Fake diamonds are not as thick, and therefore, more likely to float in water. This test is not always foolproof. Some materials that make up fake diamonds, such as cubic zirconia and moissanite, can sink if they are heavy enough.
Do all diamonds fluoresce? No. 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.
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.
It is important to note that not all diamonds with fluorescence will glow under UV light. The intensity of fluorescence can vary from diamond to diamond. Diamonds with faint fluorescence may not glow at all, while diamonds with strong or very strong fluorescence may glow very brightly.
Here's a little more to know: Simulated diamonds are also known as diamond simulants and include things like cubic zirconia (CZ), moissanite, and YAG. They can also include some natural clear gemstones like white sapphire, white zircon or even clear quartz.