Why Do Diamonds Glow Under Black Light?

A diamond ring glowing in a bluish color under UV light.

Diamonds are elusive and beautiful gemstones that have captivated many people for their brilliance and sparkle factor. But there is another aspect of them that isn’t talked about frequently and this may sound bizarre to some of you.

Did you know that diamonds can glow in a variety of colors under black light? If you are curious to know why and how it can affect you when shopping for a diamond engagement ring, you are in the right place.

In this write up, we will explain how and why some diamonds have this peculiar ability to glow in the dark. You will also find out how to use this phenomenon to your advantage when shopping for a diamond ring.

Why Do Diamonds Glow Under Black Light?

Diamonds glowing in blue, green and yellow hues in black-lighting.

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 estimated that 95% of natural diamonds with fluorescence will glow in a bluish color. Interestingly, diamonds can also glow under black light in a variety of other colors ranging from yellow, white, red, green and orange.

Gemological labs like GIA or AGS will assess a diamond’s fluorescence intensity during the grading process and identify its intensity according to the following categories: None, Faint, Medium, Strong and Very Strong.

In the strong and very strong category, the presence of fluorescence can sometimes be observed in common sources of UV lighting like the sun. This can lead to a cloudy or blurry appearance when the diamond is viewed directly under strong sunlight.

Is Fluorescence a Good or Bad Thing?

In the current market, fluorescence is often viewed as a form of “defect” and these diamonds are often sold at a discount. Personally speaking, I find this odd because fluorescence may actually be a good thing depending on your own values and perspective.

Let’s start with the negatives of buying a diamond with fluorescence. I will also address some of the common misconceptions that people have about fluorescent diamonds.

The downside to buying a diamond with fluorescence is that you may end up with a diamond that is cloudy or hazy looking. In the industry, we call this an “overblue” stone and the diamond has a distinct milky appearance that a casual observer can easily see.

While this is often portrayed to be a prevalent problem with diamonds that have strong or very strong fluorescence, it actually isn’t such a widespread issue that people think it is. Based on the statistics I’ve collected, this happens to roughly 2-3% of colorless diamonds (D, E, F) with strong/very strong fluorescence.

An overblue diamond that looks milky – GIA #2196310203

One misconception people have is that diamond fluorescence negatively affects a diamond’s sparkle and beauty. The truth is that sparkle and brilliance are determined by cut quality and not by whether the diamond has the ability to glow in black lighting.

Likewise, many people wrongly believe that fluorescence will adversely impact the durability of a diamond. While fluorescence is caused by chemical impurities in the diamond’s lattice structure, it doesn’t weaken the diamond’s hardness or strength.

So, how can fluorescence be a good thing?

Well, there are plenty of reasons to like it beyond the cool looking effect it generates when glowing in black light. First of all, diamonds with fluorescence are sold at a discounted price ranging from 5%-25% because of unfavorable market forces.

As a smart shopper, you can take advantage of this mispricing to save money when shopping for a diamond ring.

In the 2 examples above, both diamonds are well cut diamonds with similar carat weight, D color and VVS1 clarity grades. The difference between them is that the cheaper diamond has fluorescence while the more expensive one doesn’t. Visually, both diamonds will look identical and yet, there is a massive 30% price difference between them.

One other practical benefit of buying a diamond with fluorescence is that it can help improve the color appearance of diamonds in the lower color ranges. Blue fluorescence can help a diamond look whiter by counteracting the yellowish tint a diamond has and it can improve the face up view by half to one whole grade higher.

At the end of the day, fluorescence is a really subjective characteristic that depends on individual taste.

There’s nothing inherently wrong in buying a diamond with fluorescence and it is also perfectly fine if you don’t like it. What matters is that you are making your decision based on facts and not fear-mongering bullshit to push you away from buying a fluorescent diamond.

Is This a Reliable Test to Know If the Diamond is Real or Fake?

There’s a lot of misinformation being peddled on the Internet which claims that you can identify whether a diamond is real or fake based on fluorescence. For the record, fluorescence should NEVER be solely used as a criterion to determine a diamond’s authenticity.

Statistically, about a third of natural diamonds fluoresce while the majority don’t. If you are someone who is logical and can think rationally, how would it be possible to determine if a diamond is real or fake because of fluorescence?

If a gemstone doesn’t glow in dark lighting, it could fall into the category of natural diamonds that don’t have fluorescence. And you are back to square one. Likewise, you cannot jump to a conclusion that the unidentified gemstone is a diamond just because it has fluorescence. There are plenty of other minerals and gemstones that display fluorescence!

Do Lab Diamonds Glow in UV Lights Like Natural Diamonds?

Lab grown diamonds under black light with different fluorescent hues – GIA.

Yes. Lab grown diamonds can display fluorescence too and this is caused by submicroscopic structures within the crystal during the growing process. Similar to natural diamonds, blue fluorescence is the most commonly observed color in lab diamonds due to the presence of nitrogen impurities.

Depending on the specific recipe and alloys that are used in the culturing process, lab diamonds can display rarer colors of fluorescence like orange-yellow or white compared to natural diamonds.

Fun fact: If you are wondering why most diamonds glow blue, that’s because of nitrogen atoms being aligned in the carbon lattice of the diamond. But why nitrogen? Well, that’s because it is the most abundant element in our atmosphere!

Where to Buy Diamonds With Fluorescence Reliably?

When it comes to buying diamonds with fluorescence, Brian Gavin is a retailer that is well known for their signature super ideal cut diamonds. They have a specific line of diamonds called the “Brian Gavin Blue” that offers exceptional diamonds with medium – very strong fluorescence intensities.

The best part is that each diamond in the Blue line is physically inspected by Brian Gavin to ensure that they are cut with the best precision and proportions for light performance and have no ill-effect from fluorescence.

Summary – Are You Still Worried About Diamonds That Glow?

I hope this article has helped you gained a better understanding of why diamonds glow in black light and addressed some of the polarizing views that people have about fluorescence.

To recap, fluorescence can have a negative impact on a very small percentage of diamonds but the market is pricing them as if every single fluorescent stone is bad. The key here is to know what you are buying and to inspect a diamond before you buy it.

Diamonds that are negatively affected by fluorescent have milky appearances that are very obvious to even the casual shopper and can be avoided easily.

Personally, I love fluorescence as it gives the diamond a unique characteristic that is cool for showing off. It is also a cost-effective way to improve the color of a diamond without any extra cost!

On a final note, don’t be afraid of asking questions when shopping for a diamond. A good jeweler will be able to deal with and address any concerns you might have about diamond fluorescence. Good luck!

Brian Gavin is the best jeweler that offers the highest quality diamonds with fluorescence and the great thing is that they come at a price discount. James Allen and Blue Nile are 2 other vendors I recommend if you are shopping for non-fluorescent diamonds.

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