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What Effect Does Blue Fluorescence Have on a Diamond?

By Todd Gray

February 4, 2013

There seems to be a great deal of confusion about the effect of blue fluorescence upon the appearance of a diamond, especially in the range of medium blue, strong blue and very strong blue.  While there seems to be a great deal of interest in blue fluorescent diamonds by consumers at this point in time, there seems to be an equal amount of concern about whether the presence of blue fluorescence in a diamond is going to make the diamond appear “milky” or foggy.

The reality is that only a very small percentage of diamonds with blue fluorescence are negatively impacted by the presence of fluorescence, perhaps less than 2% and I am referring to 2% of diamonds with fluorescence, not 2% of gem-quality diamonds.  The basis for this estimate is based upon a statistical analysis of fluorescent diamonds conducted by the GIA Gem Trade Laboratory in 1997 in which they reviewed a random sample of 26,010 diamonds ranging in color from colorless to faint yellow and determined that 65% of those diamonds did not exhibit any degree of fluorescence when exposed to long-wave UV radiation.

Of the 26,010 diamonds examined, only 9,175 or 35% exhibited fluorescence and 3,465 of those or 38% were reported to have faint fluorescence while 5,710 or 62% of those diamonds had descriptions that ranged from medium to very strong.  Of the 5,710 diamonds which exhibited fluorescence, 5,533 or 97% of them exhibited blue fluorescence in varying intensities and only 162 of the diamonds (3%) fluoresced another color such as yellow, white or orange.  It should be noted that the GIA does not indicate a color of fluorescence for faint fluorescent diamonds.

The GIA clearly states in their report that they made a conscious decision to restrict the basis of their analysis to diamonds with blue fluorescence because of the relative rarity of colorless to faint yellow diamonds which exhibit yellow fluorescence because of “the difficulty of finding sufficient numbers of yellow fluorescent stones to conduct a parallel study.”  They proceed to state “Diamonds with extremely strong blue fluorescence and a distinctive oily or hazy appearance, often referred to as ‘overblues’ are also a concern to the industry.  In our experience, however, they are even rarer than diamonds with yellow fluorescence.”

I concur with the opinion stated by the GIA to this regard… In the 25+ years I spent as a diamond buyer, I literally graded and evaluated thousands and thousands of diamonds and during that time I recall seeing very few diamonds that were negatively impacted by the presence of blue fluorescence and every one of them had been graded as having a level of fluorescence which was “extremely strong blue” or “distinct blue” which are synonymous grading terms used to describe a level of fluorescence which is beyond very strong.  Therefore it seems like it is pretty safe to say that if you want to avoid the possible negative influence of fluorescence upon a diamond, just avoid the select few which exhibit extremely strong to distinct levels of fluorescence.

In truth, this was a factor in our selection criteria when I was the diamond buyer for Nice Ice.  We simply avoided diamonds with extremely strong and distinct blue fluorescence because we didn’t want to risk the potential effect that it might have upon the appearance of a diamond.  My late-wife Robin used to wear a 2.54 carat marquise cut, D color diamond which exhibited extremely strong blue fluorescence when examined under the long-wave UV light provided by a GIA Diamond Light in a pitch black room and the diamond often did appear to be “milky” or “foggy” when viewed in direct sunlight or in a room with UV lighting.  She actually purchased the diamond with the intent of using it as a teaching tool and would often show it to clients to demonstrate the effect which the extremely strong blue fluorescence was having upon that particular diamond.  The following picture which was provided by Brian Gavin Diamonds shows how diamonds with blue fluorescence appear when viewed under long-wave UV light in a pitch-black room, the effect is pretty cool:

Most of the diamonds which we owned and wore personally exhibited medium to strong blue fluorescence when exposed to long-wave UV light; needless to say as diamond dealers we had access to diamonds of all descriptions, the truth is that we preferred the look of blue fluorescent diamonds within the range of medium to very strong blue.  For this reason, I am a big fan of the diamonds offered within the Brian Gavin Blue collection of blue fluorescent diamonds.  Each diamond is carefully examined by Brian Gavin personally and hand-selected for maximum visual performance.  The degree of fluorescence for the diamonds selected for the Brian Gavin Blue collection ranges from medium blue fluorescence, strong blue fluorescence and very strong blue fluorescence.

While Brian Gavin is the only diamond cutter I am aware of who has chosen to specifically showcase the blue fluorescent diamonds within his inventory as a “collection” other cutters such as Crafted by Infinity and diamond dealers such as James Allen also offer diamonds with blue fluorescence.  If you’ve read other articles pertaining to diamond cut quality and visual performance on this web site, it’s no secret that I’m a big fan of the production quality of Brian Gavin and the Crafted by Infinity diamonds which are represented online by High Performance Diamonds.

I also like the fact that both Brian Gavin and Paul Sleger’s of Crafted by Infinity take a very personal, hands-on approach to their diamond selection process to the degree that I am confident that they will eliminate any diamonds from their inventory that are negatively impacted by the presence of fluorescence… at least this has been my experience.  So I would not hesitate to purchase a diamond with medium blue, strong blue or very strong blue fluorescence from either the Brian Gavin Blue collection or High Performance Diamonds.

One thing which most people probably do not realize is that the “fluorescence grade” which appears on GIA and AGS diamond grading reports is actually not a “grading factor” at all, but rather is merely an “identifying characteristic” used to describe the diamond as judged at the time of grading.  When diamonds are graded in laboratory conditions, they are examined for diamond color and fluorescence while placed upside down (table facet down, the pointed culet of the diamond facing up) with a long-wave UV light source in a room without any other light source.  This method of viewing a diamond and judging it for color (actually and absence of color) and fluorescence differs dramatically from the viewing environment provided by the average jewelry store and certainly from the environment in which the diamond will be worn.

In the real world, diamonds are set in such a way that they are almost always viewed from a top-down perspective which allows the facet structure of the diamond to help mask any imperfections (inclusions) within the diamond and makes it more difficult for people to judge the body color of a diamond… many people will not notice the warmer body color of diamonds in the J-K-L-M-N range of faint to light yellow when viewing the diamond from a top-down profile, but will immediately detect that the diamond has a warmer hue when they view the diamond from a side-profile.  Since diamonds are valued by the absence of inclusions and color, diamonds which are warmer in color, such as those in the J-Z color range, are less expensive than diamonds in the D – I color range… so you can save a little money if you can handle a little tonal value.

Likewise, diamonds with medium to extremely strong blue fluorescence tend to be priced less than diamonds without fluorescence.  This is not necessarily because fluorescence is considered to be a negative factor, but rather because of the effect of a diamond investment boom that occurred in the last century, during which several investment firms tried to set themselves apart from their competitors by advertising that the diamonds contained within their investment parcels did not have fluorescence.  Big whoop.  Like I said earlier, I happen to like diamonds with blue fluorescence and I kind of appreciate the price break…

For instance, this 1.013 carat, VS-2 clarity, F color diamond with strong blue fluorescence from the Brian Gavin Blue collection is significantly less expensive at $8,697.00 (wire transfer price) than this 1.005 carat, VS-2 clarity, F color diamond with negligible fluorescence from the Brian Gavin Signature collection which is currently selling for $9,647.00 (wire transfer price).  The reality is that the two diamonds are cut virtually identical and the only real difference is that one has strong blue fluorescence and the other does not… so why are they priced differently? Because the diamond rough with blue fluorescence costs a little bit less than diamond rough without fluorescence.

Is there a visual difference between the two diamonds?  In the study conducted by the GIA Gem Trade Laboratory in 1997, it was determined that 62% of the observers detected no visible difference in the transparency of the diamonds being compared.  There were some differences detected with regards to the perceived effect of fluorescence upon the color grade of the diamonds which leads credence to the argument that blue fluorescence might help diamonds to appear whiter than they might if they did not possess fluorescence.

The GIA used separate selection criteria for the diamonds being evaluated depending on whether the person viewing the diamonds was considered to be an average consumer, a diamond professional or an expert diamond grader.  The fact is that only the expert diamond graders were allowed to judge the diamonds for color grade and among those the results indicate that 46% of the experts did not perceive a difference in color grade for diamonds within the E-color range; 41% did not perceive a difference in color for diamonds graded within the G-color range; and 15% did not perceive a difference for diamonds within the I-color range; and only 10% did not perceive a difference in color for diamonds graded in the K-color range.

However a whopping 71% of all observers (excluding Average Observers) stated that the diamonds within a given set appeared to have different depths of color… thus it is reasonable to assume that the presence of medium to very strong blue fluorescence has a positive effect upon the perception of depth of color.  However this is as determined by people within the diamond industry who have an eye for grading diamonds for color… it is unfortunate that the GIA excluded the “average consumers” from this portion of their analysis since ultimately it is the public who is most concerned with the presence or absence of fluorescence within diamonds.

The GIA continues to say that “For each of the four color sets (E, G, I, and K) taken separately, we also saw no relationship between the strength of fluorescence and color appearance with the diamonds viewed table down, but we again saw a trend toward better color appearance with stronger fluorescence when the diamonds were viewed table-up regardless of the light source.”  Here again, it seems that the GIA concluded that medium to very strong blue fluorescence has a positive impact upon the appearance of diamond color (or absence of color) when the diamonds are viewed from a top-down perspective as they are going to be worn.

So it seems that the data provided by the GIA study on fluorescent diamonds from 1997 (Winter edition of GIA Gems & Gemology magazine) indicates that blue fluorescence does have an effect upon our ability to perceive color within diamonds… diamonds with strong blue fluorescence are more likely to be judged as having a better color appearance when viewed table-up.  The effect by the way is most noticeable in the lower color grades, such as those in the range of I-color to Z-color, and less noticeable in higher color grades such as D-G color.  This might be because blue fluorescence is essentially Mother Nature’s whitewash for diamonds and it is simply less noticeable in diamonds that already exhibit an absence of color.

About the author

A mad scientist with a passion for improving diamond cut quality to maximize light performance and sparkle factor. I speak geek in degrees of optical precision between bouts of freediving. My ghostwritten ramblings haunt the rabbit holes of information found on many diamond vendor sites. Diamond buyer, author, consultant, errant seeker of deep blue water.

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  1. As an aside, Katherine, your input made me nervous as I had never considered that an unscrupulous jeweler may swap out my wife’s beautiful NiceIce diamond for something of less quality during rhodium plating etc. It makes me rethink just who we deal with for repair/upkeep work.


    1. It is always a good idea Chris to ask the jeweler you are working with to help you plot the inclusions within your diamond on the job envelope and your receipt prior to dropping it off and to help you identify the diamond when you pick it up. We used to use an imaging system which was part of our microscope to help customers with this, it is good protection for both the customer and the jewelry store as it helps to avoid any misunderstandings… a reputable jeweler should not have an issue with this because they will understand that there are people without integrity in every industry, including our own.

  2. For those of you who are wondering about the issue of fluorescence from the perspective of an actual buyer:

    Thirteen years ago, I purchased a diamond directly from the Grays for many reasons, not the least of which was the fact that I specifically sought a D/E/F triple ideal round diamond with fluorescence. Despite living in the San Francisco Bay area, I was unable to find any brick-and-mortar jeweler who had the stone I was seeking in his inventory. A few were willing to order one for me through their colleagues, but I would have been required to purchase the stone sight unseen – as is, no returns. Perhaps more surprising was the fact that so many jewelers I met perpetuated the myth of the cloudy, hazy quality caused by fluorescence. I was given a great deal of misinformation during that time – that the stone wouldn’t hold its value, that it might become hazy, that I would never be able to upgrade it or re-sell it. Looking back, I suspect that these dealers were more interested in trying to sell me a stone from their inventory rather than trying to provide accurate information and help me find what I wanted.

    Fortunately, I found niceice and my shopping frustrations were solved.

    So, here’s my experience of owning and wearing an AGS000 F round brilliant fluorescent diamond:

    It remains the most beautiful stone I own. It is as brilliantly, stunningly sparkly and clear as the day I bought it.

    Indoors in most lighting, the stone is absolutely white. Not a trace of color, neither blue nor yellow, as expected. The notable exception to this has been in an unexpected setting. I am in anesthesia and many of the Operating Room and Endoscopy Suite overhead lights currently in use will cause my ring to emanate a slight violet-blue hue and intensify its brilliance. It is very striking, and now that I know to look for it, I have seen this same phenomenon a few times in other women’s rings, all of which exhibit medium- to strong-blue fluorescence. It is gorgeous.

    Outdoors, in low light settings or those with indirect sunlight, the stone is colorless white, as indoors, but seems to have an icier quality. However, on clear blue sky days with intense sunlight, the stone has a distinct violet-blue hue that can be made more apparent if it is adjacent to something white. This is especially true, for example, when we are skiing in Colorado (high altitude, intense sunlight, bright blue sky, white snow). On some of those days, the stone actually appears to radiate a faint blue glow and is blindingly sparkly. I have had people stop me there to ask me about it.

    Having moved a few times in the intervening years, I have been to several different jewelers for one thing or another, and every one of them has commented on the beauty of my diamond. One particularly frank jeweler even told me to “never let this diamond out of your sight in the diamond district, it’ll be swapped in seconds” when I relayed that I wanted to visit New York.

    I continue to be amazed by how unimportant the issue of fluorescence became to jewelers I asked once I had already made a diamond purchase. Some stated that they personally preferred it. I think there’s more than one lesson to be learned there.

    As an aside, I always understood that fluorescence can improve the visual quality of near-colorless diamonds, but I recently was told by a local jeweler that some in the industry are now asserting that fluorescence is of no value in colorless stones. I can tell you that this is not true. I bought a colorless fluorescent stone specifically because I did not want any discernible yellow warmth indoors. Yet, its colorless quality allows its fluorescence to be expressed more strongly because it is not masked by yellow tones. That’s the best of both traits in my mind – a brilliant white stone with the special quality of fluorescence.

    In the end, the matter of fluorescence comes down to personal preference and perhaps a little money saved by the diamond industry’s discount of these stones. The presence of fluorescence alone should not dissuade you from purchasing a diamond, but at the same time, you absolutely should understand how this quality will affect its appearance in a variety of natural and simulated light settings. Take the time to learn if fluorescence is something that you like, don’t mind, or dislike by actually viewing fluorescent diamonds alone and in comparison with non-fluorescent diamonds in different lighting situations at different times of the day. And, most importantly, remember that you should buy the most beautifully-cut and proportioned, highest quality, and most brilliant diamond that you can afford – not necessarily the largest – from a reputable source who will work with you throughout the transaction in a fair, transparent manner. In most cases, a double-take diamond is not the largest diamond, but the most beautiful to behold.

    Best of luck!

    1. Thank you Katherine for taking the time to provide such wonderful insight into what it is like to own a diamond with blue fluorescence! I am thrilled to have your input as an addition to this article because it provides a perspective that I could not imagine since I have never experienced the lighting scenario which you work under… it sounds amazing! And it is SO nice to hear from a customer of Nice Ice who is still thrilled with the diamond which they purchased so many years ago ~ it truly warms my heart! Thank you so much…

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