Fluorescence in Diamonds...Good, Bad or Ugly?

It has been established over the years, through extensive testing that approximately 30% to 35% of all natural diamonds exhibit some degree of fluorescence when exposed to UV light. So it is fair to say that most diamonds found in nature do not fluoresce.

A diamond might fluoresce under a bright sun, at the dance floor or in other places where strong fluorescent or black light is present. Fluorescence is a temporary phenomenon and once the UV light source is turned off, the diamond stops fluorescing.

Diamond grading reports in general describe the intensity in 5 grades of fluorescence as: None, Faint, Medium, Strong and Very Strong. If the fluorescence level is Medium, Strong or Very Strong, the 'colour' of the fluorescence is also stated on these reports

If you’re still wondering what diamond fluorescence is, think about how ultra-violet light makes your whites look whiter and some of your teeth glow at the discotheque. In the same context, you may want to know that when a diamond fluoresces or radiates a glow, is that fluorescence good, bad or neutral for your diamond.

Here is an attempt to demystify some of the misinformation and conjecture surrounding fluorescent diamonds, so read on . . . 

Causes & Effects of Fluorescence

Fluorescence in diamonds remains a widely misunderstood concept, both at the trade and consumer level. It is a frequently debated topic within the diamond industry and even the opinions of experienced jewellers tend to differ on this subject.

While it takes over a billion years to form in the earth’s mantle, a diamond is very likely to absorb atomic quantities of the neighbouring minerals and gases present. Trace elements such as aluminium, boron or nitrogen absorbed in these minuscule quantities during the growth phase can cause diamonds to fluoresce in varying colours.

The inherent variations in the atomic structure of the diamond crystal then act as a trigger in the presence of UV light. Ultraviolet light, which consists of high-energy waves, causes the electrons of these trace elements to pop into higher energy states. Electrons in these excited states jump orbits to release that stored energy as light as long as the UV light is present. Remove the UV light, and the electrons quickly return to their calm original state.

Fluorescence can be good or bad for a diamond’s perceived colour: faint to medium can improve a diamond’s colour whereas strong to very strong can oftentimes make the diamond look milky or hazy. Many trade professionals think that moderate levels of blue fluorescence can enhance a diamond’s visible appearance. When inspected with the naked eye, it can show up one colour higher than its actual colour. Sometimes even two colours !

In the near colourless range (I to M colours) faint or medium blue fluorescence can negate the effects of a diamond’s colour tinge. It can make a diamond with a yellow tinge appear less yellow (read: whiter) in the presence of natural daylight. We know that natural daylight always has a UV component – less or more depending on geography, location and ambient conditions.

As mentioned earlier a third of all natural diamonds display some level of visible fluorescence, and less than 5% of these exhibit fluorescence in the strong to very strong range which affect their appearance to some degree - even under normal viewing conditions, i.e. under non-UV light.

Under rare circumstances, this strong to very strong fluorescence can cause the diamond to appear milky or hazy under normal daylight. This haziness can interfere with the transparency of the diamond blocking the return of refracted light, which in turn directly impacts its brilliance. Since the most valuable and desired feature of a diamond is its brilliance, anything that diminishes or takes away from the diamond's sparkle is a negative if the intended use is for jewellery. Except if the intended is as a collector’s item, then in a quirky sort of way these ugly diamonds are rare. Ever heard of a rare ugly duckling?

Faint 'yellow fluorescence' can have a markedly negative effect on a diamond’s colour. Say you have an I, J or K colour diamond with yellow fluorescence - in full sunlight, the yellow fluorescence is sure to intensify the faint yellow colour of the diamond . In addition, diamonds with yellow or white fluorescence tend to have hazy look.

Determining and Measuring Fluorescence

GIA, the world’s premier grading laboratory and education institute for all things gems & jewellery considers diamond fluorescence an identifying characteristic. It is not a factor considered in grading of the universal 4Cs but is an important element of the overall grading report that enables the determination of a diamond's worth and identity. All laboratory grading reports describe a diamond’s fluorescence in five levels of intensity as described earlier.

GIA conducted a study some twenty years ago to understand the effect of blue fluorescence on diamond appearance. The study investigated four sets of diamonds, of 4 different colour grades (E, G, I, and K) but with differing intensities of blue fluorescence. Otherwise the diamonds in each set were as similar as possible in all other respects (size, cut grade, clarity etc). Diamond graders, trained professionals, and average observers viewed the diamonds under controlled conditions to make a judgment about their appearance.

See also: Our guide to Insights into the Diamond Industry

Here is what the study concluded: “For the average observer, representative of the jewellery buying consumer, no consistent effects of blue fluorescence on the face-up appearance of the groups of diamonds were observed. Even experienced observers did not consistently agree on the effects of fluorescence from one stone to the next”. The operative word here is ‘consistent’. Ever since the study was made public, fluorescence has been one of the most hotly debated topics in the diamond industry.

Price Impact of Fluorescence on Diamonds

Opinion on the effects of fluorescence range across the spectrum. See if you notice any visible effects of fluorescence the next time you are shopping for a diamond in a jewellery store – and then decide if fluorescence appeals to you or the other way round. Since the intention of this article is to help simplify your decision making, if you do decide to take home a fluorescent diamond.

In assigning a diamond’s colour grade, labs must examine the gem in a controlled lighting environment, designed to minimize the influence of external fluorescence. This has to be done in order to arrive at an accurate and objective assessment of the diamond’s true colour. The UV component in natural daylight can cause a shift in colour perception if the diamond is inherently fluorescent.

Even so, a likely positive outcome is that fluorescence may be seen as enhancing the diamond's colour grade, potentially increasing its desirability and perceived value which incentivise us to pay more for the diamond.... That is how the world turns.

And the reverse holds true more often. A slight hint of a lower color or a perceived negative impact of color on an already good colour diamond leads to a decrease in the perceived price.

Here are examples of when fluorescence can lower a diamond’s price:

• Strong or very strong blue fluorescence: Diamonds in all colour grades could appear hazy or cloudy but this is not a generalisation; each diamond is unique and its reaction to strong fluorescence is just as unpredictable. The impact on price here is usually the greatest.
• Medium blue fluorescence: In the context of colourless grades (D to G) – in some cases the medium blue intensity can mask the true colour of the diamond and result in a lower perceived colour. You are paying for an F, and what you see visibly is a G. Doesn't that call for a price discount ?
• Faint blue fluorescence: For colourless grades (D to G), it can have from a positive to no influence on perceived colour but can significantly impact the buyer's emotions and price perception – a common sentiment expressed is if  “Since I am paying good money for a high colour I don’t want fluorescence interfering with the colour of my diamond even if I don’t see it”. It is a fair reason for hesitation and usually works to the buyer's favour. Market dynamics dictate that the price should be adjusted to a level where the consumer feels comfortable to make that compromise. Such a diamond usually sells easily when the discount offered makes it an attractive purchase. 

Conclusions

The impact of fluorescence on diamonds and its effect on value is not a clear cut matter  and there isn’t a simple one sentence answer. Jewellery professionals disagree to what level and how much fluorescence impacts the value of a diamond. My conclusion is that it has three distinct effects  - in some cases a good or positive impact, in many more cases a bad or negative impact and in less frequent cases a strongly hideous impact. Even call it ugly!

Any degree of fluorescence in diamonds in the colourless range (D to G) is considered less desirable going by market perception, hence their prices and values tend to head lower. It need not be so ! In my opinion, fluorescence per se isn’t always a negative trait, which means you can save money by choosing a diamond with some level of fluorescence when combined with advice from a trusted jeweler.

Diamonds in the near-colourless grades (I to M) can benefit from some faint or medium blue fluorescence. In normal daylight viewing conditions, this can make the diamond appear one whole colour grade higher. It follows that you can get good value by choosing a diamond with a lower colour that has been propped up by its fluorescence. Physically viewing this diamond under differing light conditions helps you make an educated choice. And then again, it is always prudent to seek the opinion of a trusted jeweller during an in-person visit. Online stores cannot provide this valuable service.

Twenty or more years ago, fluorescent diamonds in near colourless (I-M) (read lower colour) grades attracted decent premiums over non-fluorescent diamonds, mainly in Asian and US markets. These diamonds looked whiter than their non-fluorescent counterparts primarily because fluorescence enhanced their face-up colour.

Sadly, over the past 12-15 years, perceptions have changed with the internet hastening the spread of incomplete knowledge, thus forcing the market to discount fluorescence in all colour grades, irrespective. Today the common wisdom prevailing is “the higher the colour, the more negatively fluorescence affects price”. There is no room open to negotiate.

We at Facets have consistently recommended that a diamond should be physically inspected, whenever possible, before a buying decision is made. This holds even more water if one is shopping for a fluorescent diamond which should always be viewed under a variety of lighting conditions. You will be surprised by what you see and don’t see.

Unfortunately, for online shoppers - even with today’s advanced digital imagery, it is not possible to accurately capture the face-up look of a fluorescent diamond in natural light.

I hope by now you have some clarity on the complexities of fluorescence in diamonds and can better appreciate the role of a brick and mortar retail jeweller. Online bargains are plenty to be had, but don’t let price and slick marketing be the main influencing factors in your buying decision. The jewellery professional can help you make the right decision and save you money in the long run.

I leave you to draw your own final conclusions, but one thing should by now be clear - there is no one right or wrong answer to the many mysteries of fluorescence. And fluorescence can have all three effects on a diamond - good, bad and ugly.