"Foxfire" diamond in the rough, origin Diavik Mines; Approx. 187 carats. Photo by Michelle Z. Donahue, Courtesy Smithsonian Institute

Fluorescence in Diamonds...Good, Bad or Ugly?

Demystifying the misinformation surrounding fluorescence in diamonds


Fluorescence is the glow sometimes seen when an object emits visible light. Some diamonds fluoresce when they are exposed to ultraviolet light. This can cause them to emit a bluish glow of varying intensities and less often so - a yellow, green or even a white glow.

It has been established over the years, through extensive testing that approximately 30% to 35% of all natural diamonds exhibit some degree of fluorescence when exposed to UV light. So it is fair to say that most diamonds found in nature do not fluoresce.

A diamond might fluoresce under a bright sun, at the dance floor or in other places where strong fluorescent or black light is present. Fluorescence is a temporary phenomenon and once the UV light source is turned off, the diamond stops fluorescing.

Diamond grading reports in general describe the intensity in 5 grades of fluorescence as: None, Faint, Medium, Strong and Very Strong. If the fluorescence level is Medium, Strong or Very Strong, the 'colour type' of the fluorescence is also stated on these reports

If you’re still wondering what diamond fluorescence is, think about how ultra-violet light makes your whites look whiter and some of your teeth glow at the discotheque. In the same context, you want to know that when a diamond fluoresces or radiates a glow, is that fluorescence good, bad or neutral for your diamond.

Here is an attempt to demystify some of the misinformation and conjecture surrounding fluorescent diamonds, so read on . . . 

Causes & Effects of Fluorescence

Fluorescence in diamonds remains a widely misunderstood concept, both at the trade and consumer level. It’s a frequently debated topic within the diamond industry and even the opinions of experienced jewellers tend to differ on this subject.

When it takes over a billion years to form in the earth’s mantle, a diamond is very likely to absorb atomic quantities of the neighbouring minerals and gases present. Trace elements such as aluminium, boron or nitrogen absorbed in these minuscule quantities during the growth phase can cause diamonds to fluoresce in varying colours.

The inherent variations in the atomic structure of the diamond crystal then act as a trigger in the presence of UV light. Ultraviolet light, which consists of high-energy waves, causes the electrons of these trace elements to pop into higher energy states. Electrons in these excited states jump orbits to release that stored energy as light so long as the UV light is present. Remove the UV light, and the excited electrons gradually return to their calm original state.

Strongly fluorescent diamonds GIA

Photo courtesy GIA.

Here is a example of very strong fluorescence in a variety of colours. Notice the extreme haziness of the two yellow diamonds exhibiting green fluorescence
Diamonds can fluoresce in a variety of colours - predominantly blue. The visible colour range includes yellow, orange, white, green and very rarely red. Blue is by far the most common colour of diamond fluorescence occurring in over 95% of diamonds that fluoresce.
When a diamond exhibits fluorescence, the perception of its face-up colour is affected in unpredictable ways. I use the word ‘perception’ emphatically because that is precisely what it is. It’s the perception of colour that changes and never the true colour itself.

Fluorescence can be good or bad for a diamond’s perceived colour: faint to medium can improve a diamond’s colour whereas strong to very strong can oftentimes make the diamond look milky or hazy. Many trade professionals think that moderate levels of blue fluorescence can enhance a diamond’s visible appearance. When inspected with the naked eye, it can show up one colour higher than its actual colour. Sometimes even two colours.

In the near colourless range (I to M colours) faint or medium blue fluorescence can negate the effects of a diamond’s colour tinge. It can make a diamond with a yellow tinge appear less yellow (read: whiter) in the presence of natural daylight. We know that natural daylight always has a UV component – less or more depending on geography and ambient conditions.

As mentioned earlier a third of all natural diamonds display some level of visible fluorescence, and less than 5% of these exhibit fluorescence in the strong to very strong category which could alter their appearance to some degree - even under normal viewing conditions, i.e. non-UV light.

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Photo courtesy: diamondreview.com

A very strong blue fluorescence in a diamond may show up as a milky haze even under normal daylight conditions

Under rare circumstances, this strong to very strong fluorescence can cause the diamond to appear milky or hazy under normal daylight. This haziness can interfere with the transparency of the diamond blocking the return of refracted light which in turn directly impacts its brilliance. Since the most valuable and desired feature of a diamond is its brilliance, anything that diminishes or takes away from the diamond's sparkle is a negative if the intended use is for a piece of jewellery. Except if it is intended as a collector’s item, then in a quirky sort of way these ugly diamonds are rare. Ever heard of a rare ugly duckling?

In some cases the stone can look ugly and should be avoided except as a collector’s item because in a quirky way, these ugly diamonds are rare

Faint 'yellow fluorescence' can have a markedly negative effect on a diamond’s colour. Say you have an I, J or K colour diamond with yellow fluorescence - in full sunlight, the yellow fluorescence is sure to intensify the faint yellow colour . In addition, diamonds with yellow or white fluorescence tend to have hazy or milky hues.

Determining and Measuring Fluorescence

GIA, the world’s premier grading laboratory and education institute for all things gems & jewellery considers diamond fluorescence an identifying characteristic. It is not a factor considered in grading of the universal 4Cs but is an important element of the overall grading report that enables the determination of a diamond's worth and identity. All laboratory grading reports describe a diamond’s fluorescence in five levels of intensity as described earlier.

Various degrees of fluorescence

Photo courtesy: withclarity.com

GIA conducted a study some twenty years ago to understand the effect of blue fluorescence on diamond appearance. The study investigated four sets of diamonds, of 4 different colour grades (E, G, I, and K) but with differing intensities of blue fluorescence. Otherwise the diamonds in each set were as similar as possible in all other respects (size, cut grade, clarity etc). Diamond graders, trained professionals, and average observers viewed the diamonds under controlled conditions to make a judgment about their appearance.

See also: Our guide to Insights into the Diamond Industry

Here is what the study concluded: “For the average observer, representative of the jewellery buying consumer, no consistent effects of blue fluorescence on the face-up appearance of the groups of diamonds were observed. Even experienced observers did not consistently agree on the effects of fluorescence from one stone to the next”. The operative word here is ‘consistent’. Ever since the study was made public, fluorescence has been one of the most hotly debated topics in the diamond industry.

Price Impact of Fluorescence on Diamonds

Opinion on the effects of fluorescence range across the spectrum. See if you notice any visible effects of fluorescence the next time you are shopping for a diamond in a jewellery store – and then decide if fluorescence appeals to you or other way round. And the intention of this article is to help simplify your decision making, if you do decide to take home a fluorescent diamond.

In assigning a diamond’s colour grade, labs must examine the gem in a controlled lighting environment, designed to minimize the influence of external fluorescence. This has to be done in order to arrive at an accurate and objective assessment of the diamond’s true colour. The UV component in natural daylight can cause a shift in colour perception if the diamond is inherently fluorescent.

On the one hand, one possible perspective is that fluorescence may be seen as enhancing the diamond's color grade, potentially increasing its desirability and perceived value. Consequently, this can create the illusion of a higher value and incentivise us to pay more for the diamond.. That is how the world turns.

And the reverse certainly holds true. A slight hint of a lower color or a perceived impact of color on an already good colour diamond leads to a decrease in the expected price.

Here are examples of when fluorescence can lower a diamond’s price:

  • Strong or very strong blue fluorescence: Diamonds in all colour grades could appear hazy or cloudy but this is not a generalisation; each diamond is unique and its reaction to strong fluorescence is just as unpredictable. The impact on price here is the greatest.
  • Medium blue fluorescence: In the case of colourless grades (D to G) – in some cases the medium blue intensity can mask the true colour of the diamond and result in a lower perceived colour. You are paying for an F, and what you see visibly is a G. Doesn't that call for a discounted price?
  • Faint blue fluorescence: For colourless grades (D to G), it can have from a positive to no impact on perceived colour but can significantly impact the buyer's emotions and price perception – a common sentiment expressed is if  “I am paying good money for a high colour I don’t want fluorescence interfering with the colour of my diamond even if I don’t see it”. It is a fair reason for hesitation and usually works to the consumer’s favour. Market dynamics dictate that the price should be adjusted to a level where the consumer feels comfortable in making a compromise. Such a diamond usually sells easily when the discount offered makes it an attractive purchase. 


The impact of fluorescence on diamonds and its effect on value is not a clear cut matter  and there isn’t a simple one sentence answer. Jewellery professionals disagree at what level and how much fluorescence impacts the value of a diamond. My conclusion is that it has three distinct effects  - in some cases a good or positive impact, in many more cases a bad or negative impact and in some less frequent cases a visibly ugly impact.

Any degree of fluorescence in diamonds in the colourless range (D to G) is considered less desirable going by market perception, hence their prices and values tend to head lower. It need not be so. In my opinion, fluorescence per se isn’t always a negative trait, which means you can save money by choosing a diamond with some level of fluorescence when combined with guidance from a trusted jeweler.

There are no defined rules to help you along the way, so let your head guide you but let your heart lead the way

Diamonds in the near-colourless grades (I to M) can benefit from a faint or medium blue fluorescence. In normal daylight viewing conditions, this can make the diamond appear one whole colour grade higher. It follows that you can get good value by choosing a diamond with a lower colour that has been supported by its fluorescence. Physically viewing this diamond under differing light conditions helps you make an educated choice. And then again, there is always a need to seek the opinion of a trusted jeweller during an in-person visit. Online stores cannot provide this valuable service.

'J' colour stones viewed in standard daylight conditions. Notice the visibly whiter colour tinge of the fluorescent stone on the right.   
diamond-fluorescence-comparison-j-diamond-1024x505 (2)

Photo courtesy: withclarity.com

Twenty or more years ago, fluorescent diamonds in near colourless (I-M) (read lower colour) grades attracted decent premiums over non-fluorescent diamonds, mainly in Asian and US markets. Because these diamonds looked whiter than their non-fluorescent counterparts. More so because the manner in which fluorescence enhanced their face-up colour made them unique! Sadly, over the past 12-15 years, things have changed with the internet hastening the spread of incomplete knowledge, thus forcing the market to discount fluorescence in all colour grades. Today the prevailing wisdom is “higher the colour, the more fluorescence negatively affects price”.

We at Facets have consistently recommended that a diamond should be physically inspected, whenever possible, before a buying decision is made. This holds even more water if one is shopping for a fluorescent diamond which should always be viewed under a variety of lighting conditions. You will be surprised by what you see and don’t see:

Unfortunately, for online shoppers - even with today’s advanced digital imagery, it is not possible to accurately capture the face-up look of a fluorescent diamond in natural light.

I hope by now you have some clarity on the complexities of fluorescence in diamonds and are able to appreciate the role of a brick and mortar retail jeweller. Online bargains are plenty to be had, but don’t let price and slick marketing be the main influencing factors in your buying decision. The jewellery professional can help you make the right decision and save you money in the long run.

I leave you to draw your own final conclusions, but one thing should by now be clear - there is no one right or wrong answer to the many mysteries of fluorescence. And fluorescence can have all three effects on a diamond - good, bad and ugly.

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Suresh H.

Written by Suresh H.

Respected international diamantaire and industry expert with a deep knowledge of the industry, GIA trained diamond grader, researcher and writer about all things related to diamonds.

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