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Understanding Diamond Fluorescence

Is diamond fluorescence good or bad? Best tips for buying a diamond with fluorescence

Michael Fried
Michael Fried

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Bottom Line Recommendation

When purchasing a diamond, its important to take fluorescence into account. When flourescence is utilized correctly, you can find a superb diamond like this one from James Allen.  If you ignore flourescence, you can make a huge mistake like this diamond from Blue Nile.

What is Diamond Fluorescence?

Fluorescence in diamonds is the glow you might see when the diamond is under ultra-violet (UV) light (i.e. sunlight or black light). Approximately 30% of diamonds glow at least somewhat. When exposed to ultra-violet light, these diamonds fluoresce different colors. 99% of the time, the glow is blue, but on rare occasions, diamonds glow white, yellow, green, or even red in color. The GIA grades fluorescence in diamonds as None, Faint, Medium, Strong and Very Strong. 

So if you’re wondering what diamond fluorescence is, think about how ultra-violet light makes your whites look whiter and your blacklight posters glow. In the same way, some diamonds fluoresce when they’re under UV light. 

Depending on the diamond, fluorescence can either improve the diamond’s color or make it appear hazy. In this guide, we share how to evaluate fluorescence in diamonds. 

Is diamond fluorescence good or bad? 

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 Blue Fluorescence, 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. 

Here are examples 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, E and F Color diamonds with any Fluorescence:
    Diamonds in the colorless range (D-F) don’t benefit from fluorescence. They’re actually considered less valuable, so their price and desirability are also lower.

Strong Blue Fluorescence in Diamonds


HaIf 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 fluorescence 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.

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 fluorescence 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, always check into the retailer’s return policy- just in case
  6. Buy fluorescent diamonds from a reputable retailer 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 it 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 Fluorescent diamonds usually appear hazy
  • Medium Blue Fluorescent diamonds rarely appear hazy
  • Slight/Faint Blue Fluorescent 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.

Fluorescence Can Improve 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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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.

Brian Gavin’s Blue Line

An interesting alternative if you’re buying online is to consider purchasing a diamond from Brian Gavin’s “Blue” line.  These stones have all been hand-picked by Brian Gavin himself for exhibiting no signs of milkiness or cloudiness. This is where it is apparent that finding a reputable retailer to buy fluorescent diamonds from is crucial when you are looking to obtain a high-quality diamond.

Additionally, the fluorescence improves the diamond’s appearance by making the stone look more colorless without any negative side effects.  The best part is that they’re as brilliant as his “Signature” line of Hearts & Arrows perfectly cut diamonds with one exception – they’re much cheaper. This stunning 1.17ct round diamond from Brian Gavin is a perfect example where you get a gorgeous diamond that is perfectly cut. Due to the fluorescence, its a bit brighter and cheaper.

We’ve been eagerly recommending these diamonds since early 2012 and everyone that has followed our advice has been extremely pleased.

Buying Diamonds Locally vs Online

Buying a diamond online with medium or lower fluorescence is cheaper than buying a strong blue fluorescent diamond locally. If you’ve decided to shop locally, though, ensure that any strong blue flourescent diamond is not hazy. It’s always best to evaluate a fluorescent diamond in person if you can. You can ask to see how the diamond looks under different light sources (i.e. sunlight vs. indoor lighting).

Unfortunately, for online shoppers—even with James Allen’s advanced photography—you won’t be able to see how the diamond looks face-up in direct sunlight. That’s why we recommend staying away from strong blue flourescent diamonds online. But remember that reputable vendors like Blue Nile and James Allen have 30-day free returns in case your fluorescent diamond ends up looking hazy.

Here are general buying recommendations for fluorescence:

H, I or J color diamonds: Feel free to look for a diamond with Medium Blue fluorescence like this 1.10ct Round cut from Blue Nile or this 1.04ct Round diamond from James Allen for an added bonus. It can make your stone look slightly whiter. If not, your stone will still look great without it.

Diamond with a G or higher color: Find a diamond with either no fluorescence or faint fluorescence. Otherwise, consider a diamond from the Brian Gavin Blue Collection. Aim for an I or J color stone to get the best value.

Because these are general guidelines, every diamond won’t fall into these recommendations. For guidance on a specific diamond, contact us.

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. Save 25% on studs and earrings! and  Save 10% off Lab Created Diamonds during limited time sale!
What we love about them:
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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
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