Diamond fluorescence is a subtle but important factor in understanding your diamond purchase and the physical appearance of your diamond in different lighting conditions. Below we’ll analyze each fluorescence grade and how it affects diamonds of different color grades. The grades of diamond fluorescence discussed below are based on what the GIA refers to as fluorescence intensity, or the degree of fluorescence that a diamond exhibits when exposed to UV (ultra violet) light. Along with each fluorescence category we’ll note the percentage of diamonds available online that received each grade (based on the inventory of top online jewelers).
One quick note before we start. There are several ways to refer to diamond fluorescence and the language may change depending on which source you are reading at any given time. In this article we refer to the fluorescence intensity grades as None, Faint, Medium, Strong, and Very Strong. But you may also see these referred to as No/NON, FNT, MED, STG, and VST respectively. The AGS (American Gemological Society) even has a unique grade called Negligible that we’ll discuss later. Additionally, when discussing fluorescence below we’ll use the terms “fluorescence” and “fluorescence intensity” interchangeably and when referring to fluorescence color (e.g. Blue) we’ll state that explicitly. OK – now that that’s out of the way, let’s get started…
You should know that from a visual standpoint certain diamond color grades pair better with certain diamond fluorescence grades. For example, the highest color grades (D – F) tend to have much higher prices when they are paired with None fluorescence than with Faint or Medium fluorescence. Meanwhile, lower color grades (J or lower) tend to price pretty consistently across None, Faint, and Medium fluorescence.
This pricing phenomenon occurs because fluorescence can help offset some of the coloration present in a diamond, but when there is no coloration present any fluorescence is typically viewed as undesirable and unnecessary. Very Strong fluorescence can even make a diamond appear hazy or oily (as we’ll soon discuss) and for this reason it tends to consistently be less favored than the other fluorescence grades.
The table above presents the findings of a recent study conducted by StoneAlgo. The results show the price differences for various fluorescence and color combinations as one moves across the fluorescence spectrum. As you can clearly see, the higher color grades like D and E price significantly higher for None and Faint fluorescence than for Medium and Strong fluorescence.
For lower color grades the pricing is fairly flat as many buyers tend to favor some fluorescence to help offset the natural color present in J or K color diamonds. We did not study the changes in pricing for Very Strong fluorescence as there were not enough samples (only 0.6% of diamonds) in the study to yield clear results. The diamonds studied were all GIA triple excellent diamonds in the 1 carat range with VS1 clarity. The price changes are based on the average price per carat for each color grade.
Based on our diamond database of over one million diamonds, None (sometimes called NON or No Fluorescence) is by far the most common degree of fluorescence intensity with about 67% of diamonds graded as such. When the GIA grades a diamond as having None fluorescence, it doesn’t necessarily mean there isn’t any fluorescence whatsoever. Instead, it means that the fluorescence is so faint that it is essentially non-existent. None of the diamond color grades will be affected by None fluorescence, we think of it as the baseline to which we can compare all other fluorescence grades.
As you can see from the fluorescence/color price table, None fluorescence commands a higher price than any other fluorescence grade but may command a slightly lower price in J color and lower on a case by case basis. This pricing phenomenon is due to the fact that fluorescence can actually help to offset the appearance of color in a diamond and the color grade at which people begin to perceive color is typically the J/K range. So, a K color diamond with Medium fluorescence is viewed by some buyers as preferable to a K color diamond with None fluorescence since the former will appear slightly whiter when exposed to sunlight.
Recommended color grade pairings for None fluorescence: all diamond colors, but especially recommended for colorless diamonds.
About 18% of GIA certified diamonds available online are graded with Faint fluorescence, making it the second most common fluorescence grade. As its name implies, Faint fluorescence means that the diamond exhibits a minimal amount of fluorescence when exposed to UV light and that the intensity of this fluorescence is not significant enough to seriously affect the diamonds appearance. However, Faint fluorescence is often recommended for buyers of lower color grades because it can help to slightly offset some of the color saturation associated with those diamonds (specifically when they are exposed to natural sunlight). Diamonds with Faint fluorescence should also typically command a lower price than those with None fluorescence in the higher color grades (D – I), but may command the same price or even a premium to None fluorescence in certain diamonds in the near colorless or faintly colored range.
Recommended color grade pairings for Faint fluorescence: all diamond colors, but especially recommended for G or lower color grades to offset minor color saturation.
Medium fluorescence is typically the level at which buyers become nervous that the diamond’s appearance will be negatively impacted by the intensity of the diamond’s fluorescence in colorless diamonds (D – F color). However, diamonds with Medium fluorescence can offer great value in the right situations and even positively impact lower color grades like J or K color that may otherwise show some color saturation. While the impact is typically minimal and only apparent under UV light, Medium fluorescence (sometimes called MED on a certificate) helps to offset the (typically) yellow color of a diamond by adding a blue hue to the stone in natural sunlight or UV light. This makes the diamond appear whiter and can often give the diamond more life.
Recommended color grade pairings for Medium fluorescence: G or lower color grades, but especially recommended for J or lower color grades to offset color saturation.
In certain cases diamond fluorescence can negatively impact a diamond by making it appear hazy or oily when exposed to UV light (like the diamond pictured below). For this reason, it’s highly recommended that you see a diamond with Strong fluorescence in real life or videos of the diamond in natural sun light to determine if the diamond will exhibit these negative effects. For K color diamonds or lower, Strong fluorescence is often sought out to help offset the color saturation that exists within the diamond. The diamond pictured above is a J color with Strong fluorescence that looks great in natural sunlight. Typically, Strong fluorescence should be avoided in the higher color grades (D – G) as it is more likely to negatively impact these diamonds.
Recommended color grade pairings for Strong fluorescence: J or lower color grades, especially for faintly colored diamonds.
Very Strong fluorescence is rare and has a higher likelihood of negatively impacting a diamonds visual appearance by making the stone look hazy or oily. For this reason we don’t recommend you seek out Very Strong fluorescence.
Recommended color grade pairings for Very Strong fluorescence: none.
Negligible fluorescence is a grade specific to the AGS (American Gemological Society) which does not differentiate between None and Faint fluorescence. It is the grade given to diamonds that exhibit a minimal level of fluorescence and should not impact the appearance of the diamond much in any color grade.
Recommended color grade pairings for Negligible fluorescence: all diamond colors.
Diamond fluorescence is not necessarily good or bad. As mentioned above, in certain situations diamond fluorescence can help offset some of the color in lower color grade diamonds (like K color) and make those diamonds appear slightly whiter. Additionally, a small amount of fluorescence may make a diamond appear to have more “life”, meaning the diamonds look “more sparkly”. On the flip side, too strong of fluorescence can sometimes make a diamond look hazy or dull, but this is very rare.
Sunlight is approximately 10% UV light, which means that diamonds with fluorescent properties will exhibit their fluorescence slightly when exposed to sunlight.
If the diamond has fluorescence of any level there is a chance you will notice it under UV lighting. The stronger the intensity of the fluorescence the more likely it will show strengths of fluorescence when exposed to black lights.
None fluorescence is a GIA designation that means the diamond has so little fluorescence that is it essentially nonexistent while Negligible fluorescence is a category specific to AGS certified diamonds that is basically a catchall category combining the GIA’s none and faint fluorescence categories.
Diamond fluorescence can come in a variety of colors but the most common and preferable is blue fluorescence. Some diamonds are listed as strong blue fluorescence, which just means that it has Strong fluorescence of the Blue variety. Other colors of diamond fluorescence include green, purple, orange, yellow, and white.
Picking out the perfect diamond is a lot of work. That’s why we founded StoneAlgo back in 2017 to help buyers find better value and higher quality diamonds. If you have any questions about the possible impact of fluorescence on a diamond’s physical appearance you can always chat us the GIA ID and images in the chat bubble on the bottom right of this page. Good luck with your search and let us know if we can help.