A real diamond will reflect light easily, and provide you with a disco ball or rainbow-like display. You can use a flashlight or lamp to do this and it will work best with white light rather than yellow. If the stone absorbs the light, then there's a chance that it's a fake.
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.
A real diamond provides an exceptional sparkle since it reflects white light extremely well. In addition, diamonds can also reflect fire or colored light in a beautiful display. Compared to a stone like Cubic Zirconia, you'll be able to see a huge difference in the white and colored light sparkle.
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.
In most cases, diamonds fluoresce blue. This cancels out the slightly yellowish color in most diamonds, resulting in a whiter appearance in sunlight. In artificial light, there's little UV intensity more than a few inches from the 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.
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.
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.
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 see, diamonds are a magnet for grease/oil as their surfaces muck up easily. A dirty stone doesn't sparkle because light simply can't enter the diamond and causes it to appear dull.
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.
Fluorescence is the glow you sometimes see when an object emits visible light. Some diamonds fluoresce when they are exposed to long-wave ultraviolet (UV) rays from sources like the sun. This can cause them to emit a bluish light or more rarely, a yellow or orangy 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.
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.
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.
The Fog Test
Diamonds are made completely of carbon, an organic material. They conduct heat so if you blow on a diamond the foggy surface will dissipate immediately. If you blow on a stone and the foggy surface sticks around, then the stone isn't a real diamond.
Diamonds both reflect and refract, which explains why they glitter so brilliantly. Diamonds are cut to have many flat sides, or facets. Each facet is polished to be extremely smooth. When light waves hit a very smooth surface, they reflect at the same angles at which they hit.
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.
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.
Roughly 30% of diamonds contain a certain level of boron, which causes the precious gems to glow when they're exposed to ultra violet, also known as "blacklight." The level of boron present in the diamond determines how much light the diamond will emit when exposed.
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.
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.