There is perhaps no characteristic of a diamond on which you will find more disagreement among diamond professionals than diamond Fluorescence.  For this reason, it is also a subject that causes much confusion among diamond professionals as well as consumers.

Diamond florescence refers to the effects of ultraviolet light on a diamond.  According to the GIA (Gemological Institute of America), approximately 25% to 35% of all diamonds have some degree of fluorescence.  Diamonds that have fluorescence will exhibit a “bluish” glow when exposed to ultraviolet light.  In most cases, this glow is minimal and will never be seen outside of laboratory conditions.

A study conducted by the GIA concluded several key findings that are significant with regard to fluorescence:

1) Nearly 1/3 of all diamonds certified by the GIA (Gemological Institute of America) have some degree of fluorescence noted on the grading report.

2) Only 10% of those diamonds with fluorescence had any degree of florescence that may affect the appearance of the diamond.  Quite simply, this means that fluorescence, even when indicated on a GIA grading report, has no significance to the diamond 90% of the time.

3). For the overwhelming majority of diamonds, the strength of fluorescence has no widely noticeable effect on appearance. In fact, the average person could not make a distinction between a diamond with fluorescence and a diamond without fluorescence.

4). In many instances, observers preferred the appearance of diamonds that have medium to strong fluorescence.  Again – Most observers preferred the appearance of diamonds that are fluorescent!

According to another diamond industry “authority” known as the “Rapaport Report”  (a publication for the Diamond trade), “Fluorescence may add value to lower color stones as it gives the stones a whiter, brighter appearance.”

Now that I have given you the findings of the GIA study on fluorescence, I will share some of my thoughts on the subject . . .

As stated above, there is perhaps no element of a diamond grading report that is more misunderstood and controversial than that of fluorescence. The negative thoughts with regard to fluorescence date back to different times of the diamond trade.

Firstly, in the days before diamond certification, fluorescence was considered to be “bad” because a diamond with fluorescence might be seen to be better than than it really was – and therefore, the buyer may be fooled. If you really think about this, fluorescence was thought to be bad because it made a diamond look better!

Additionally, another reason for the negativity about fluorescence dates back to 1980 when there was an “Investment Diamond” craze in which people were sold a bill of goods about buying diamonds as an “Investment”.  During this time, it was thought that in order to buy an ‘investment grade diamond”, the diamond must be only the best quality (i.e., D to F color, Flawless or VVS clarity) and have no fluorescence.

Regardless of the thoughts about fluorescence at the time, the value of diamonds skyrocketed based on investment speculation before falling precipitously. People who invested in diamonds during this time ended up losing a lot of money – but the connotation that fluorescence is a “bad thing” has lived on for no apparent reason!

So where does this bring us today . . .

It is my opinion that “Faint” fluorescence means nothing!!  Faint fluorescence is something that will never be seen by the consumer and something that has absolutely zero effect on the beauty of a diamond! “Faint” fluorescence is something that should NEVER deter you from buying a particular diamond.

It is my opinion that “Very Strong” fluorescence should be AVOIDED.  A “Very Strong” fluorescence grade is that which is most likely to give a diamond a “smokey” or “milky” or “cloudy” appearance.  Diamonds that are of Very Strong fluorescence trade at discounts of 20% to 50% less than similar diamonds with none or lesser degrees of fluorescence..

The issue of fluorescence is more convoluted when dealing with Medium or Strong fluorescence.  In almost all cases within these fluorescence grades, the fluorescence will have either no effect of the overall beauty of the diamond or, alternatively, the fluorescence will have a beneficial effect. In many cases, medium or strong fluorescence will enhance the beauty of a diamond – particularly in “JKLM+” or lower colors. In these colors, the diamond will appear whiter when mounted in a ring than a similar diamond without fluorescence.

In some cases, strong fluorescence may be a negative factor.  In such cases, the diamond may have a milky or cloudy appearance as mentioned above with regard to “Very Strong” fluorescent diamonds. It is my opinion that Strong Blue fluorescent diamonds should be acceptable in many cases – with the exception of DEF/IF -VS graded diamonds. As with the case of Medium fluorescence, “Strong” fluorescence is usually a benefit to lower color diamonds as these diamonds will look considerably better when mounted than a similar lower color (JKLM+) diamond without fluorescence. In DEF/IF-VS graded diamonds, Strong blue fluorescence should be usually be avoided.

In terms of diamond pricing, a diamond with medium fluorescence should be priced approximately 2% to 15% below that of a similar diamond without fluorescence. The amount of this reduction depends on the color grade of the diamond.  In lower colors, the price differential is insignificant.  In DE and F color diamonds and VVS clarity diamonds, the price differential should be more significant.

A diamond with Strong fluorescence should be priced at 15% to 30+% less than a similar diamond without fluorescence. This discount will be less as you drop down the color scale as the benefits of fluorescence become more desirable. Strong fluorescence in high quality diamonds (DEF/VVS-VS) can be 30% or more, especially in cases where the strong fluorescernce is noticeable and/or “milky” in appearance.

I realize that this brief discussion may run counter to other information one may find with regard to the subject of fluorescence.  One must understand that fluorescence is often a subject used by a diamond seller to dissuade one from purchasing a diamond from another seller. For instance, “That diamond has fluorescence; You shouldn’t buy that diamond!” It is BS comments like this that perpetuate the controversy of this subject.

As a professional within the diamond industry for more than 40+ years, I can honestly tell you that I purposely selected a diamond with Medium fluorescence for my wife’s engagement ring!! Yes, I purposely chose a “I” color diamond with Medium Blue fluorescence!   I honestly believe that fluorescence can be beneficial to a diamond in that it can enhance the overall beauty of a diamond and bring down the cost of a diamond by a few percentage points.

Perhaps, the GIA has said it best when it comes to fluorescence . . . “A diamond’s appearance must be taken as a whole. . . Other factors can influence appearance more strongly than fluorescence, such as how the diamond has been cut, . . .” Perhaps the most important statement on the subject is also from the GIA: “On GIA’s Diamond Reports, fluorescence is a description, not a grade”.

The bottom line is this. What makes a diamond one of the most treasured items of nature is the beauty of a diamond. There are many different things noted on a GIA grading report. We have turned the beauty of a diamond into characteristics noted on a piece of paper. A diamond is about the beauty of the diamond. – and not the piece of paper!

NOTE: This discussion of fluorescence deals with Blue fluorescence which is the type of fluorescence most commonly found. Any other fluorescence -yellow or white fluorescence which is indicated as such on a GIA grading report should ALWAYS BE AVOIDED. This type of fluorescence always has a negative impact on the beauty of a diamond.