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June 3rd 2023

Unlocking the Mysteries of Diamond Fluorescence

By Devin Jones

Below we'll show you real statistics from diamond shoppers on StoneAlgo and help you understand when diamond fluorescence is a helpful cost saving feature, and when it's a terrible mistake.

What is diamond fluorescence?

Diamond fluorescence refers to the emission of visible light that occurs when a diamond is exposed to ultraviolet (UV) light sources. This mesmerizing phenomenon is caused by the presence of certain trace elements within the diamond's atomic structure, such as nitrogen. When these elements absorb UV light, they emit a visible glow, which can vary in intensity and color.

The GIA, renowned for its expertise in gemstone grading and identification, has developed a comprehensive grading system to evaluate diamond fluorescence. This system categorizes fluorescence into five grades: None, Faint, Medium, Strong, and Very Strong. Each grade represents the intensity of fluorescence observed in a diamond when exposed to UV light. By assigning a fluorescence grade, the GIA aims to provide buyers with valuable information that can influence their diamond purchasing decisions.

Understanding the significance of diamond fluorescence is crucial because it can affect the appearance of a diamond in certain lighting environments. Some diamonds with strong or very strong fluorescence may exhibit a milky or hazy appearance under certain lighting conditions, diminishing their overall visual appeal. On the other hand, diamonds with faint or medium fluorescence can sometimes exhibit a subtle enhancement of color or a unique glow, which some individuals find appealing.

Let's investigate some stats on how common each color grade is and how popular they are for StoneAlgo diamond shoppers.

None vs Faint vs Medium vs Strong Fluorescence

The below images show I color diamonds with fluorescence grades of none, faint, medium, and strong.

None fluorescence diamond
Faint fluorescence diamond
Medium fluorescence diamond
Strong fluorescence diamond

Click on a diamond for more details and videos

While 2/3 of all diamonds have none fluorescence, there are instances in which faint or medium fluorescence are sought out by diamond buyers to help improve the appearance of their diamond. Typically this affects the demand for faint and medium fluorescence in near colorless and faintly colored diamonds, but it can also be a great way to save money on a colorless diamond (an E color with faint fluorescence for example).

Fluor Grades % on StoneAlgo Pairs Best With
None 67.4% All color grades
Faint 14.9% G or lower
Medium 10.3% H or lower
Strong 4.4% J or lower
Very Strong 0.85% Avoid completely

Now, just because a diamond has fluorescence doesn't mean it's going to glow if it's ever exposed to a black light or other strong UV source. In fact, for near colorless or faint colored diamonds (basically color grades G, H, I, etc.), faint or medium fluorescence can make the diamond appear slightly whiter as we'll explain in greater detail below. However, some diamonds with Very Strong Fluorescence can appear cloudy or hazy and for this reason we recommend you avoid these diamonds completely if you're shopping online.

GIA diamond fluorescence grades none, faint, medium, strong, and very strong in natural light and under UV light

Why do some diamonds have fluorescence?

Some diamonds have fluorescence due to the way the diamond grew over billions of years deep beneath the earth's surface (or in the case of lab grown diamonds, over months within a specialized manufacturing process that grows the diamond). Sometimes when a diamond is forming, trace elements of aluminum, boron, or nitrogen are absorbed by the diamond. These elements are what gives off a fluorescent glow when certain diamonds are exposed to UV light.

How does diamond fluorescence affect price and appearance?

Some diamonds benefit from a little fluorescence, while others don't. Below we'll explain which types of diamonds are best paired with which fluorescence grades and how these pairs affect each diamond's price.

Colorless diamonds, the highest color grades that include D, E, and F color diamonds, tend to have much higher prices when they are paired with None fluorescence than with Faint or Medium fluorescence. This is because the shoppers who are willing to pay for these high color grades tend to be very picky, and tend to lean towards none fluorescence. It's also because fluorescence does not lend any sort of advantage to colorless diamonds as it can to near colorless and faintly colored diamonds.

Some near colorless diamonds (G, H, I, and J) can actually benefit from a little fluorescence because it helps them appear slightly whiter (especially J color diamonds). This slight advantage leads to these diamonds being priced pretty consistently across None, Faint, and Medium fluorescence as we'll show in the table below.

1 Carat D VS1 Diamond with None Fluorescence
1 Carat D VS1 Diamond with Very Strong Fluorescence

The two diamonds shown above are both 1 carat D color VS1 Clarity diamonds, however the diamond shown on the left has a fluorescence grade of None and costs $8,547 while the diamond shown on the right has a grade of Very Strong and costs $6,433. Buying the diamond with None fluorescence costs 33% more than the Very Strong fluorescence, even though they may look very similar to the untrained eye.

To see how diamond fluorescence affects price for various diamond shapes and color grades, check out our diamond price calculator where you can play with real-time diamond data and see how fluorescence affects price.

Below is a chart depicting the various discounts that shoppers can expect to receive for fluorescence grades within a particular color grade. For example, medium fluorescence in a D color diamond leads to a 18.2% discount versus a D color diamond with None fluorescence. For a J or K color diamond, medium fluorescence is priced almost equal to None and Faint 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 (like in a D color) 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.

Diamond fluorescence can make some diamonds cheaper as shown in this table

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.

None Fluorescence (present in 67% of diamonds)

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. The below diamonds both have None fluorescence, the one on the left is a 1 carat D color diamond and the one on the right is a 1 carat J color diamond.

1 Carat D Color Diamond with None Fluorescence
1 Carat J Color Diamond with None Fluorescence

As you can see from the fluorescence/color price table mentioned in the prior section, 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.

Faint Fluorescence (present in 18% of diamonds)

Comparison of none, faint, and medium fluorescence in k color 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. While we typically recommend fluorescence for near colorless grades and lower, E color  and F color diamonds with faint fluorescence are great value plays and will look icy white in any color of engagement ring setting.

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 (present in 8.7% of diamonds)

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. Based on our research, I color diamonds with medium fluorescence are a great value play that can also look totally white depending on the carat weight and shape of your diamond.

Recommended color grade pairings for Medium fluorescence: H or lower color grades, but especially recommended for J or lower color grades to offset color saturation.

Strong Fluorescence (present in 5.4% of diamonds)

J color diamond with strong fluorescence

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 (present in 0.6% of diamonds)

Very strong fluorescence in a diamond

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 (an AGS exclusive)

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.

Is diamond fluorescence good or bad?

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.

Will sunlight affect my diamond’s fluorescence?

Sunlight is approximately 10% UV light, which means that diamonds with fluorescent properties will exhibit their fluorescence slightly when exposed to sunlight. It's also important to remember that a diamond will reflect its environment. The below diamond is an H color diamond with no fluorescence that was photographed outdoors. The strong blue appearance is not fluorescence but rather the reflection of the clear blue daytime sky.

Will my diamond glow at the bowling alley or night club?

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.

What is the difference between negligible and none diamond fluorescence?

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.

What different colors of diamond fluorescence exist besides blue fluorescence?

Diamonds with green, blue, and yellow fluorescence viewed under normal light and black light

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.

What You Need To Know About Diamond Fluorescence

Diamond fluorescence is a subtle but important factor in understanding your diamond purchase and the physical appearance of your diamond in different lighting conditions. Above we analyzed each fluorescence grade and how they affect diamonds of different color grades. The grades of diamond fluorescence discussed above 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’ve noted the percentage of diamonds available online that received each grade (based on the inventory of top online jewelers).

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've referred to the fluorescence intensity grades as None, Faint, Medium, Strong, and Very Strong. You may also see these grades referred to as No/NON, FNT, MED, STG, and VST fluorescence, respectively. The AGS (American Gemological Society) even has a unique grade called Negligible. Additionally, when discussing fluorescence we've used 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…

A pear shaped diamond with strong fluorescence under a black light

A Final Note on Fluorescence

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.

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