Diamond Fluorescence - Good or Bad?

The answer is both… or neither.

When exposed to invisible ultraviolet (UV) light, many diamonds temporarily luminesce, emitting visible light of different colors and different strengths. Sunlight and indoor fluorescent lights contain varying amounts of UV radiation. A significant percentage of diamonds in the market have some degree of fluorescence. The vast majority of those are blue, but in rare cases white, yellow, orange and red fluorescence are also seen.

Diamond fluorescence is caused by submicroscopic structures within the crystal. (Blue fluorescence is most commonly associated with the presence of nitrogen atoms aligned in specific arrays within the carbon lattice.) In most cases fluorescence is simply an identifying characteristic and not a performance characteristic, and is therefore NEITHER good nor bad.

In some cases, strong or very strong fluorescence can make a diamond appear cloudy, diminishing its transparency and eye appeal. Such diamonds are often described as having an oily, hazy or milky appearance. In these cases it is obviously BAD.

Medium or stronger blue fluorescence tends to mask yellow body color so diamonds in the lower color range can appear a shade whiter in lighting environments with sufficient UV wavelengths. In these cases it is 'theoretically' GOOD.

However, recent science has demonstrated that the fluorescent effect is diminished dramatically as the distance from the light source is increased. In almost all normal indoor viewing circumstances the distance from the light source is too great to excite the fluorescence effect. Therefore, the idea that the appearance of diamonds in lower colors is improved by fluorescence is largely unfounded. So, in terms of visual quality it is usually NEITHER good nor bad especially when worn in one of our many diamond engagement rings.

In terms of price, fluorescence often reduces the price of a diamond and can be viewed as a GOOD thing for a value shopper, especially one who happens to like the phenomenon of fluorescence. But resale value and liquidity can often take an even bigger hit, so a long term view should be considered before deciding on a diamond with significant fluorescence. *More on that subject below.

A related concern impacting the value of fluorescent diamonds has been a topic of much discussion in the trade in recent years and has to do with the possibility of laboratory over-grading of color of diamonds with this property. Because laboratory color grading is done in light environments that do contain UV and the grading is done with the diamond in very close proximity to the UV source (typically only several inches away), there is concern that the fluorescent effect can mask the true body color leading to higher color grades for these stones. *Independent surveys have been done that show serious problems in color grading accuracy of fluorescent diamonds (see referenced article below). If the grade on the report is higher than the true body color and the appearance of the diamond does not benefit from the fluorescence under normal observation because of distance from the light source, then fluorescent diamonds actually look worse than the grade would indicate. In this case it is obviously BAD.

Diamonds in the colorless range (DEF) receive no appearance benefit from fluorescence, and the market penalizes these diamonds in terms of value depending on the strength of the fluorescence. Thus, a D color with Very Strong fluorescence would be heavily devalued.

Diamonds in the lower color ranges are not devalued as much by fluorescence with prices partially supported by the perception that these diamonds might receive some whitening benefit from the property, assuming transparency is not compromised and the stone is not over-graded for color.

The market has been historically rather fickle with regard to diamonds fluorescence. In the early days “Blue White” diamonds were highly prized. These were diamonds in the colorless range with strong blue fluorescence and no deleterious visual effects. The term became so pervasive in the marketing of diamonds that the Federal Trade Commission in 1938 felt compelled to pass regulations for the use of the term! The diamond trade also had a term for those “blue whites” that prominently display the problematic milky effect. They were referred to as “over blues” and that term is still used by members of the diamond industry.

One of the perceived negative aspects of diamond fluorescence is that an authentic gem could be confused with early simulants, some of which also had this property. With the advent of the commercial use of black lights in public places such as discothèques, consumers could become aware that their diamond was very different! That could be off-putting if you were not prepared for it.

As mentioned earlier, diamonds (particularly in the colorless range) are devalued on the market today based upon fluorescence levels. On the wholesale level diamonds are discounted by 15% or more on the basis of strong or very strong fluorescence. That lost value is compounded at the retail level. The penalty is further exacerbated in the second-hand market to the point that liquidity itself is compromised.

Over the years there have been temporary cycles of interest in highly fluorescent diamonds, but in the modern market many buyers are cautious about it. The market today seems to perceive fluorescence in a couple of distinctly negative ways. First, there is an assumption that the milky effect that is seen in some strongly fluorescent stones must be present to some extent in diamonds of lower strengths. And secondly, the purity of the diamond is suspect because of the presence of a “defect” causing the fluorescent effect. For these reasons and the others outlined above, A CUT ABOVE® Super Ideal Diamonds are required to have negligible fluorescence.

As mentioned above, fluorescence is primarily an identifying characteristic, rather than a quality characteristic. Faint fluorescence will not be detectable to an observer in real life situations, and is considered of negligible importance by AGS Laboratories (more below). But due to some perceptions in the market, even faint fluorescence can impact the price of certain diamonds. This is especially true in the very top grades. Getting a discount is certainly ok, but future liquidity may be a consideration for some.

Diamond fluorescence is assessed in the lab with the aid of a set of fluorescent master stones and specific viewing angles. Interestingly, fluorescence can occur in localized zones within the diamond and can be more or less visible depending on the viewing angle. A vivid example of this phenomenon is the diamond pictured below. In this diamond the area within the stone that is emitting light is very localized and the strength of the fluorescence is highly directional.

Multiple areas of fluorescence are also possible within the same diamond and can display distinct colors or create a mixed color. Such diamonds are very rare.

It is important to note that the first graphic above (GIA Diamond Fluorescence Comparisons) illustrates the GIA reporting scale. American Gem Society Laboratories (AGSL) considers None and Faint together as “Negligible” since neither have any impact on visual appearance.  Even the GIA designation of "None" represents a range including diamonds that contains some fluorescence, according this statement from the GIA report check website:

A striking illustration of this fact can be seen in the image below. All the diamonds in this eternity band are certified GIA “None” giving us a snapshot of the range of the None category.

Another distinction between the labs is that GIA determines a diamond's fluorescence in table-down position whereas AGSL uses the table-up view. More information on how loose diamonds are graded can be found on our pages about the American Gem Society Laboratories.

Despite claims by many in the trade and associated perceptions in the market, the GIA found that fluorescence does not make a diamond look better. The biggest study ever undertaken to understand the visual effects of fluorescence on diamond was done by the GIA and published in Gems and Gemology in 1997. The study involved carefully selected sets of diamonds in various colors and degrees of fluorescence, and involved three groups of observers; laboratory graders, jewelry trade members, and average observers. The diamonds were observed in a variety of specific lighting environments. The results of the study suggest that diamond fluorescence has very little impact on visual appearance. In its conclusion the authors state "One interesting aspect of this study was that non-trade observers could not make meaningful distinctions. For this group, which would be considered most representative of the jewelry-buying public, fluorescence had no over-all effect on color appearance or transparency". Data from the trained observers indicated a mild positive impact color in the table-up view, and even smaller negative impact on transparency. It should be noted that “over blues”, very strong blue fluorescent diamonds displaying prominent milkiness, were not included in the test sets used in this study. For more information you can download the full GIA study titled A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds.

*An article published in the Journal of Gemmology 2010 entitled entitled “ The over-grading of blue-fluorescent diamonds: the problem, the proof and the solutions” by Michael D. Cowing presents the issue along with the results of a 25 stone survey.

As discussed above, even the top labs in the world differ on their methodology and reporting of fluorescence. However, in each lab the process of observing and reporting is highly controlled and consistent. But such is not the case out in the field where jewelers and appraisers use a wide variety of devices and techniques to assess fluorescence. These various instruments contain light sources that emit variable wavelengths of UV and VV stimulation resulting in a wide range of possible observations. Therefore, while a diamond may have a GIA report showing faint, or an AGS report showing negligible fluorescence, a gemologist in the field may very well assess it as medium or even strong.

In 2013 GIA did an in-depth study of this problem and concluded:

It is therefore advisable to rely on laboratory reporting for an accurate assessment of fluorescence. If a field test by a trade professional indicates a strong possibility that an error was made in the lab, a re-check by the lab should be requested.

The Whiteflash diamond review team carefully examines the fluorescence of every diamond we offer as part of our comprehensive gemological evaluations. We use the most updated fluorescence detection device offered by the GIA - the GIA UV Lamp and Viewing Cabinet®, accompanied by a reference block with test strip.

There is no right answer to this question. It depends on preference, budget, and future plans. Understanding the impacts of Fluorescence will help you decide for yourself what is right for YOU.