Diamond Fluorescence

Is Diamond Fluorescence Bad?

There is a full spectrum of opinions on fluorescence in diamonds. Some people love it and some avoid it altogether. It is a characteristic that can have a significant impact on value and is therefore something that consumers need to carefully consider when shopping for a diamond.

The color and strength of fluorescence are primarily identifying characteristics, but in some cases fluorescence can impact the visual appearance of the diamond. According to GIA 25-35% of diamonds fluoresce to some degree when exposed to ultraviolet light, a major constituent of sunlight. All but a small fraction of those fluoresce blue.

In a small number of cases, usually in the strong and very strong categories, fluorescence can cause a loss of transparency giving the diamond a hazy, milky or oily appearance when exposed to UV light of sufficient intensity.

Blue fluorescence can also mask some yellow color in a diamond making it appear visually whiter. This is commonly thought to be a benefit for diamonds of lower color. However, in most indoor lighting environments the UV component is not strong enough to activate the fluorescent effect.

The masking effect can be activated during color grading in the lab, leading to concerns among the trade of over-grading of color. Modern color grading is done in lighting environments where the diamonds are analyzed very close to fluorescent tubes containing a UV component. This can result in the diamond being given a higher color grade than that of its true body color.

At different times throughout history blue fluorescence has been treated differently by the market. Today the characteristic generally lowers diamond values, usually in proportion to the strength of fluorescence. Diamonds of high color and clarity are penalized more severely than those in the lower ranges. In lower color and clarity combinations fluorescence has little effect on values, and some diamonds may even trade a little higher with this property.

There is a devoted segment of the consumer market that loves blue fluorescence and they seek out diamonds with this characteristic. But the issue is not a simple one and consumers should consider the pros and cons when making their buying decisions. Future values are difficult to predict, but it is clear that fluorescence has variable affects on pricing and can impact the ability to sell or trade a diamond. Consumers are therefore encouraged to deal with vendors offering good trade-up policies.

See for yourself...

The two photos below show the same 1.34ct diamond with Very Strong Blue Fluorescence. The photo on the left shows what the stone looks like under normal lighting conditions. The photo on the right shows the same stone mounted in a ring with a strong UV light pointed at it activating the blue fluorescence.

Diamond FluorescenceDiamond Fluorescence
1.34ct I VS1 graded Very Strong Blue Fluorescence by GIA
Photo of loose diamond on left by Whiteflash
Posted by TotalNewbie

And now the nitty gritty...

A GIA survey on the visual appearance of blue fluorescent diamonds found that “for the average observer, meant to represent the jewelry buying public, no systematic effects of fluorescence were detected.” This is most likely due to the fact that in most lighting conditions, even those containing some UV, the intensity is not high enough to activate the fluorescence.

The article states that fluorescence has gone through cycles in terms of popularity. There was a time when D-F colorless fluorescent diamonds were highly prized and referred to as "blue-white". But the term became so widely misused that it was eventually prohibited under US trade laws.

Internet shopping is putting downward pressure on the value of fluorescent diamonds. Many shoppers browsing large inventories online simply bypass any diamond with fluoresce in their search, leading to liquidity problems and further discounting. This can be an advantage for a shopper looking for a fluorescent diamond.

Discounting Fluorescent Diamonds

There are three primary reasons why fluorescent diamonds are discounted: Concern for transparency, concern for color grading accuracy, and concern for future value and liquidity.

Transparency - the effect of milkiness/haziness - is reportedly rare, even in higher strengths. And considering that normal viewing conditions do not activate the fluorescent effect, this concern is probably over emphasized.

Over-grading of color is a concern of many members of the trade due to modern grading practices using fluorescent tube lights that contain a UV component. At viewing distances of a few inches, the UV in the grading lights can be intense enough to stimulate fluorescence making the diamond appear whiter to the grader. A study in 2010 published in The Journal of Gemmology revealed alarming inaccuracies in the color grading of diamonds with fluorescence.

The position that GIA has taken on the issue is that UV light is present in many viewing environments, so it follows that color should be graded in realistic lighting. In making this case they have not addressed the reversal of the longstanding GIA policy that diamonds can only be color graded accurately in lighting free of UV.

Liquidity is something that most buyers think about at the time of purchase. In the future will I easily be able to sell or trade this diamond? Because a significant portion of the market avoids fluorescence, the pool of potential buyers is much smaller. All else being equal this makes fluorescent diamonds less liquid, and makes it more likely that offers will be lower in the secondary markets.

Lesser concerns are the fact that while some love it, other people may be put off by seeing their diamond glow under black lights such those popular in nightclubs. There is also a mistaken perception by some that the anomalies in the diamond’s atomic structure that cause fluorescence are considered “defects”.

To some extent fluorescent diamonds are also discounted because many jewelry salespeople are not able to explain the property to consumers. When the word “fluorescence” is written on a grading report, the diamond becomes harder to sell. Imagine a salesperson saying: “Fluorescence is visible light emitted by electrons when a diamond is excited by a higher frequency energy source like ultraviolet light.” Many shoppers lose interest!

Extreme Diamond Fluorescence

Some diamonds have extremely strong fluorescence and appear oily or cloudy like the one in the picture below. This diamond has extremely strong fluorescence in direct (left) and indirect shaded (right) cloudless mid morning sunlight. In direct sunlight it has a strong milky blue cloudiness that makes the stone very dull (photo on left). But on the right side, even in strong lighting, the stone sparkles beautifully.

The fluorescent effect in some other lighting can be observed as a bluish tint that does not dull the diamond's brightness or fire. Milkiness is not desirable but the GIA study found them to be very rare.

Diamond Fluorescence
Posted by Garry H (Cut Nut)

When you are considering stones with Very Strong or Extremely Strong Fluorescence, it is wise to compare them side by side with non-fluorescent diamonds in shaded daylight, which has a lot of ultraviolet light. You can also use a UV filter like a small sheet of Lexan.

Faint Diamond Fluorescence

A diamond with barely discernible fluorescence is reported by GIA to be “Faint”. The AGS Laboratories report faint fluorescence under the term “Negligible” – a category consisting of the two GIA designations of None and Faint. Another difference between the two labs is that GIA grades fluorescence table down and AGSL grades from the table up view. This and other variables can lead to some differences in the strengths reported by these and other labs.

Other Diamond Fluorescence Colors

Rarely diamonds fluorescence a color other than blue. Yellow, red, orange, white and green are known. This is considered desirable if the diamond is a fancy color of the same hue as the fluorescence (it can make it more intense). Colorless diamonds with yellow or orange fluorescence will appear to be a lower color when seen in light with a strong UV component. The photos below show how yellow fluorescence enhances the color of a yellow diamond. The photo on the far left shows the yellow diamond in diffuse natural light. The middle and far right photos show the same stone display yellow fluorescence in direct sunlight and under ultraviolet light.

Yellow Diamond FluorescenceYellow Diamond FluorescenceYellow Diamond Fluorescence
Kite Shape Yellow Diamond with Strong Yellow Fluorescence
Posted by davi_el_mejor

Diamond Phosphorescence

When the UV light is turned off, fluorescence ceases instantly, but some rare stones will phosphoresce after exposure. The Wittelsbach-Graff Diamond and The Hope Diamond show intense orange-red phosphorescence. The Hope and The Wittelsbach-Graff both phosphoresce after exposure to shortwave uv light, but they do not exhibit fluorescence during exposure to shortwave or longwave uv light. This unique property adds mystery to these incredible and historical diamonds.

The Hope Diamond
The 31.06ct Wittelsbach-Graff Diamond and The 45.52ct Hope Diamond
Photo by Chip Clark, Smithsonian

People will sometimes choose a fluorescent diamond over a non-fluorescent stone, and many diamond enthusiasts actually seek them for this interesting property. An additional bonus is that they usually cost less! By understanding diamond fluorescence more fully you can weigh all the pros and cons and make the choice that is just right for you.

Special thanks to Whiteflash Inc. Vice President Bryan Boyne, G.G., for his contributions to this guide.

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