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How to View Diamonds Under a Blacklight

Gabriel Garcia/Demand Media

As the old saying goes, "Diamonds are a girl's best friend," yet knowing you have a quality diamond, not a flawed gem or a fake, can ensure the friendship lasts forever. When paying top dollar for a piece of jewelry, you want to know the diamonds are flawless and real. Black light, or ultraviolet light, testing helps buyers determine the quality of a diamond. Flawed diamonds, diamonds that have been treated with fluorescence and Moissanite all look different from quality diamonds under a black light.

Things You'll Need:

  • Diamond
  • Black Light

Getting Started

Gabriel Garcia/Demand Media

Create a dark environment. In a small room, turn off any lights and cover any windows or other light sources.

Gabriel Garcia/Demand Media

Turn on the black light. Begin scrutinizing your diamond.

Gabriel Garcia/Demand Media

Look for a blue hue. Diamonds that exhibit a definitive blue color are usually genuine and lack many flaws. Each diamond is a bit different, but if your diamond shows anything from a slight blue color to one that is dark, deep and rich in hue, you have a real diamond.

Gabriel Garcia/Demand Media

Look for bright white colors. Flaws in a diamond will appear white under a black light. If your entire gem is bright white it is possible that it is not as pure as you would have hoped. Stones subjected to a lot of fluorescence also appear bright white. You can check the fluorescence rating on the diamond's certificate; it will be rated on an EGL USA scale. Just because a diamond appears white under a blacklight, that doesn't mean it is fake or flawed. The blacklight test just gives an indication that it could be fake or flawed.

Gabriel Garcia/Demand Media

Avoid stones that are green, yellow or gray. If the diamond is even slightly yellow, gray or green under a black light, the stone could be Moissanite. Moissanite is created by humans from silicon carbide and is not a true diamond.

Gabriel Garcia/Demand Media

Turn on the lights. If your diamond showed up white while under the black light, look for a cloudy or hazy appearance in your gem. If you do see any haziness, this is an indication your stone is of a lesser quality.


While a stone that shines white under the black light may not always mean that it has been heavily dealt fluorescence, or that it is not real, it may be a sign. There are other methods to check, such as X-ray tests, heat tests and weighing.


  • Use a diamond dealer that you trust and that is reputable. A black light test is only one of many things to consider using when you are buying. You should look for a diamond certificate and other forms of rating your gem as well.
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