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What Is Diamond Fluorescence (And Why It Matters)?

Is diamond fluorescence good or bad and does it effect a diamonds value?

By Mike Fried,

So you’re looking to buy a diamond and start hearing the word fluorescence thrown around. What does it mean? Some jewelers tell you it’s a good thing, some tell you it’s terrible. Who is telling the truth? Who is right? Truthfully, both can be right and both could be wrong. We’ll try to walk you through diamond fluorescence and get to the bottom of it.

What is diamond fluorescence? Fluorescence refers to the glow you might see when the diamond is under ultra-violet (UV) light (i.e. sunlight or black light). 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. In this guide, we share how to evaluate fluorescence in diamonds. 

To help you with the diamond buying process we lean on our expertise and experience. The author of this article, our CEO, Mike Fried has over 20 years of experience in the diamond industry. Mike started from the bottom, sorting and evaluating hundreds of thousands of diamonds to learn every facet (pun intended) of diamond quality and value. Mike followed that up by spending years buying and selling diamonds on the wholesale market as well as selling tens of millions of dollars worth of diamonds to diamond retailers.

Here’s what we’ll cover in this article:

How does diamond fluorescence look under UV light?
Diamond fluorescence – Diamond Pro explanation video
Should I buy a diamond that exhibits fluorescence?
Is diamond fluorescence good or bad?
7 tips on fluorescence
Strong blue fluorescence in diamonds
Does fluorescence improve diamond color?
Hesitations regarding fluorescence in diamonds

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Diamond Fluorescence Under a UV Light

Diamonds with Medium to Very Strong Blue fluorescence will react to UV light by exhibiting a ghostly blue hue. From a visual perspective, this has minimal impact. Unless you work at a nightclub, you aren’t likely to spend your day seeing the diamond flashing from UV light.

Fluorescent diamonds under a UV light

If the diamond only glows when exposed to ultra-violet light, then it should naturally only matter if you are someone who spends their days in dark rooms with black light lamps. But the fact is, most diamonds exhibiting strong blue fluorescence appear slightly to severely hazy in regular lighting conditions.
If you’ve done your homework and googled diamond fluorescence, then you might have read about a certain GIA study claiming that even strong blue is almost always entirely imperceptible to the average diamond consumer.

Fluorescence in reference to diamonds still remains to be a widely misunderstood concept. When we talk about the fluorescence of a diamond, we are referring to the glow it has when it is exposed to ultra-violet light, and when it exhibits a blue color it appears higher in color than its true body color.

Diamond Pro Video on Fluorescence

Should I Buy a Diamond with Fluorescence in it?

When purchasing a diamond, it’s important to take fluorescence into account. When fluorescence is utilized correctly, you can find a superb diamond like this one from James Allen.  If you ignore fluorescence, you can make a huge mistake like this diamond from Blue Nile. A November 2019 report in Rapaport found that most consumers don’t think about fluorescence when diamond shopping and “the trade is missing out on an opportunity”.

While fluorescence can have a positive or negative effect on the diamond’s physical appearance (as we explain below), it definitely has a negative impact on price. If you are purchasing a diamond with an eye towards its investment value (especially a DEF color), avoid any fluorescence.

Does Fluorescence Have a Positive or Negative Impact On a Diamond? 

Fluorescence can be good or bad: it can improve a diamond’s color or make the diamond look hazy. When diamonds have Slight or Faint Fluorescence from GIA, for example, they don’t appear cloudy. In fact, the slight fluorescence can make the diamond appear more white. But when fluorescence makes the diamond hazy, the stone is less transparent. Light won’t reflect as well and the diamond won’t be as clear or beautiful. 

What to know about fluorescence

The GIA grades fluorescence in diamonds as none, faint, medium, strong and very strong. Here are explanations of when fluorescence can lower a diamond’s quality:

  • Strong or very strong blue fluorescence: These diamonds usually appear hazy or cloudy.
  • Medium blue fluorescence with a high color grade (G or better): These diamonds also usually appear milky or hazy.
  • D color, E color and F color diamonds with any fluorescence:
    Diamonds in the colorless range (D-F) don’t benefit from fluorescence. They’re actually less desirable and therefore less valuable, which lowers the diamond price per carat.

7 Tips on Diamond Fluorescence

  1. It is up to your own tastes to determine if the fluorescence of the diamond is good or bad
  2. Fluorescence can often improve the color of the diamond
  3. Strong blue does not necessarily mean there will be a negative effect on the diamond’s overall color and appearance
  4. Faint fluorescence of a diamond can actually save you money without having to miss out on brilliance
  5. When shopping for fluorescent diamonds at a jeweler, always check into the retailer’s return policy- just in case
  6. Buy fluorescent diamonds from a reputable retailer with a GIA certificate to ensure they’re high-quality
  7. When shopping, it is okay to ask to see the diamonds under UV and normal lighting, as well as inquire about how they may look when exposed to daylight

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High Fluorescence Means Hazy Diamonds

I can tell you with absolute certainty, that their research is bunk. I have seen tens, if not hundreds, of thousands of diamonds in my career and I can tell you without question the following:

  • Strong/Very Strong Blue diamonds usually appear hazy
  • Medium Blue diamonds rarely appear hazy
  • Slight/Faint Blue diamonds never appear hazy

If the diamonds you are looking at have a strong or very strong blue fluorescence, then they will most likely appear hazy, oily, or cloudy and this will also cause the diamonds to appear less transparent. When comparing diamonds back to back, you will definitely see a difference between a diamond with strong fluorescence and one with little or none. It is also important to note that this extreme level of haziness for a fluorescent diamond is also not typical and is not as common as you may think when you are discussing diamonds that are H and lower.

Does Fluorescence Improve Diamond Color?

Some studies done on fluorescence do make one claim that is correct. Fluorescence will usually improve the appearance of color in the diamond.

As I suggested in my bottom line recommendation above, if you are buying a diamond with a color H or lower, seek out a diamond with medium blue fluorescence. 

I am hesitant to suggest looking for a diamond with strong blue fluorescence since even lower colors can occasionally look milky and hazy when they have strong blue fluorescence. But the lower you go in color grades, the less likely it will be milky. Here is an example of a beautiful J color diamond from James Allen that benefits from the strong fluorescence.

A medium blue fluorescent diamond color can even help counteract any yellowish tint the diamonds may have and can make them appear much whiter. In effect, this will make the diamond color and appearance an entire color grade higher.

Fluorescence can make the diamond shine and sparkle more than a diamond that lacks fluorescent properties.

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FAQs About Diamond Fluorescence

Do fluorescent diamonds glow in the dark?

Diamonds with fluorescence (especially strong blue grades) can glow in the dark. You will only see that blue hue under an ultra-violet (UV) light. This occurs in 30% of natural diamonds.

Do lab-grown diamonds have fluorescence?

No, lab-grown diamonds do not have fluorescence. While it’s theoretically possible, we have not seen any in inventory.

Hesitations Regarding Fluorescence

I am also hesitant to suggest medium blue fluorescence when purchasing a diamond with very high color (G or better) since on rare occasions even a medium blue fluorescent diamond can exhibit milkiness or haziness when the color is exceptionally high.

If, of course, you are buying a diamond in person and not online, then it’s in your best interest to specifically ask for a diamond with strong blue fluorescence. You are best off asking us about any specific diamond you are looking at. Contact us and we’ll help you out.

It will be more affordable, and since you are there in person, you can see for yourself whether or not the diamond exhibits haziness or milkiness. Make sure to ask to see the diamond in a variety of different lighting settings, if possible.

James Allen James Allen is the leader in online diamond sales. Their imaging technology is the same as inspecting a diamond with a jeweler's loupe. They have the largest exclusive loose diamond inventory online and fantastic prices. They also have the nicest collection of lab created diamonds online.
What we love about them:
  • No questions asked returns within 30 days of shipment. James Allen will send you a paid shipping label to return the ring.
  • Lifetime Warranty
  • Free International Shipping
  • Free prong tightening, repolishing, rhodium plating and cleaning every 6 months
  • Provide insurance appraisals
  • One free resizing within 60 days of purchase
  • Free ring inscriptions
  • Best-in-class high quality imagery of all diamonds in stock
  • 24/7 Customer Service
  • Best-in-class packaging
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What we love about them:
  • No questions asked returns within 30 days of shipment. Blue Nile will send you a paid shipping label to return the ring.
  • Lifetime Warranty
  • Free Shipping
  • Free prong tightening, repolishing, rhodium plating and cleaning every 6 months
  • Provide insurance appraisal
  • One free resizing within the first year of purchase
  • High quality images of about half of their diamonds
  • 24/7 Customer Service
  • 100% credit towards future upgrades (must be at least double in value)
  • Best in class fulfillment
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About the author

Mike Fried Mike Fried Mike Fried has over 25 years experience in the diamond industry working with Leo Schachter Diamonds, Moshe Namdar Diamonds, and joining The Diamond Pro in 2007. He is recognized as an industry expert and has been quoted in publications such as Us, People, Page Six, The Next Web and more.

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