Summary: What is Fluorescence?
Fluorescence is the blue-white light effect that one sees in diamonds under an ultraviolet light.
Fluorescence is a (normally) blue-white light effect that some diamonds exhibit. However, fluorescence can only occur in the presence of ultraviolet light (UV light). It is for this reason that UV light is used by diamond mining operations to aid in finding diamonds. Overall, fluorescence has little to no effect on the light display of a diamond under normal lighting conditions.
Put simply, fluorescence is the effect of ultraviolet (UV) light on boron atoms that are found within some diamonds. As we know, diamonds are the result of carbon deposits that have been subjected to tremendous pressure and heat found beneath the earth's surface over the course of millions of years. The carbon deposits normally also contain certain foreign mineral atoms. During the formation of the diamond some of these foreign mineral atoms become trapped within the diamond's crystalline structure. One of these foreign minerals is boron. As we have mentioned, it is the boron that is found in some diamonds that causes the fluorescent display when the diamond is exposed to ultraviolet (UV) light.
How Fluorescence Affects a Diamond
While fluorescence has no affect on the physical properties of the diamond, it can have an affect on the optical properties of a diamond. A diamond will receive a rating of "None" to "Very Strong" as far as the amount of fluorescence that can be seen in a given diamond. The level of fluorescence can change the perceived color of the diamond when it is viewed in normal lighting situations allowing for a slightly more yellowish diamond to appear white.
The reason for this change is due to the effect of light on the diamond and the length of the light spectrum in which the diamond is being viewed. Most light sources contain some measure of UV light within the color spectrum displayed. Sunlight, fluorescent lighting, and standard light bulbs all contain UV light within their light spectrums. These are the light sources in which most people will normally be viewing their diamonds.
In order to determine whether or not a diamond has fluorescence, the diamond must be viewed under a UV rich light. Most of us are familiar with UV lights, as they are popularly known as "black lights". If you have ever been in a nightclub, then you will probably be familiar with seeing white clothing, and even teeth, glowing with a notable bluish light. This is due to the UV lights that are used in such places. Much like the nightclub scenario, in which your clothing ceases to have the bluish glow to it once you move away from the black light range, diamonds also cease to exhibit this display when removed from UV light.
While fluorescence is not going to be as obvious under most normal lighting conditions, it may slightly affect the diamond's optical properties. For example, a diamond that has "strong" fluorescence may cause a diamond with a color grade of I to appear clearer than its color grade when it is viewed in sunlight. What causes this is the effect of fluorescence on the diamond. The slight yellow of the I grade diamond is somewhat offset by the faint blue that results from a "strong" fluorescence when the UV in the sunlight causes the fluorescence in the diamond.
It is still debated as to whether or not fluorescence can actually have any noticeable effect on the diamond's clarity. In 1997 GIA presented their findings on the effects of fluorescence on diamonds. The results of their research found that only about 1% of polished diamonds had a level of fluorescence that was strong enough to have a negative effect on the clarity of a diamond. In this tiny percentage of diamonds, known as "over blues", diamonds can appear to be oily, milky or hazy due to fluorescence. One of the world's most famous diamonds is an "over blue", the 127 carat Portuguese Diamond, currently held at the Smithsonian in Washington DC.
The research actually found that fluorescence had either no effect or varying levels of positive effect on any given diamond (apart from the "over blues" which were discounted from the study). In fact, the color grades of I-K had the most positive effects as a result of fluorescence, with their color looking notably clearer when the fluorescence was "strong" or "very strong". The study rated the observations of both diamond professionals as well as those who had no connection to the diamond trade. The professionals had a difficult time finding differences between diamonds with fluorescence and diamonds without, often disagreeing on the same diamonds. Non-trade observers had an even more difficult time than the professionals.
Diamond graders and other diamond professionals utilize UV lights in order to determine if a diamond displays fluorescence. If it does, it will have a faint to very strong bluish glow to it in the presence of the UV light. GIA and other labs note on their grading certificates as to whether or not a diamond displays fluorescence. It does not take the presence or absence of fluorescence into account in the overall grading of the diamond, but merely notes the fluorescent level. A diamond will be noted to have one of the following levels of fluorescence:
- None (or Inert or Negligible)
- Very Strong
There are those, such as Rapaport of the Rapaport Report, who believe that fluorescence is still a notable negative factor on diamonds. This belief does not come out of an actual effect of fluorescence on the optical or physical properties of the diamond. Instead, this view comes from a pragmatic understanding that any additional factors on a diamond certificate are normally viewed with a negative light in the consumer's eye. Therefore, the presence of fluorescence must bring down the cost of a diamond.
This is also due to the fact that there is a strong disagreement on the light used in the grading of a diamond. When a diamond is graded in a light that contains UV light, the UV light within the grader's light could potentially cause a diamond to be given a higher color grading if the diamond has fluorescence. Therefore, the argument goes, the potential for a higher color grading than is deserved creates the need to bring down the value of a diamond that exhibits fluorescence.
Fluorescence was first discovered and named in 1852 by a British scientist by the name of George G. Stokes. He discovered that the mineral fluorite (also known as calcium fluoride) would give off a bluish light when exposed to a strong ultraviolet light source. He named this phenomenon after the mineral he first discovered it in. It is for this reason that this is now known as fluorescence.
What actually occurs when you see fluorescence is the result of reactions occurring within the atomic structure of the object in question, in this case, a diamond. When UV light hits the diamond, any boron within the crystalline lattice structure of the diamond is affected. The electrons of the atoms absorb the high-energy photon that is emitted by the UV light. This absorption causes electrons to jump to the next orbit around the atomic nucleus. The electrons then drop back to their original orbit, re-emitting the energy at a lower energy level, and with a lower wavelength photon.
The result of this atomic reaction is that you see a (normally) bluish light when a fluorescent diamond is exposed to UV light rays. The UV light is transmitting at a high energy level that is not within the visible light spectrum. Once the light photons are re-emitted back to the viewer's eye, they are at a lower energy level, and so are within the visible light spectrum. In diamonds this reaction normally ceases at the moment that the UV light source is removed. Diamonds do not exhibit the phenomenon known as phosphorescence, in which the light reaction continues for a time after the removal of the UV light.
Fluorescence does not have a huge impact on a diamond's optical properties, but can have a dramatic impact on its pricing. When looking through diamonds, it is important to check whether or not the diamond exhibits fluorescence. If it is indicated as having slight to medium, it should be of no concern. If the diamond has strong fluorescence it will be important to consult with a diamond specialist or view it for yourself, under different lighting conditions, and decide what effect you feel the fluorescence has. Less than 1% of the diamonds with fluorescence are affected in a negative way. If the diamond looks good to you, and more importantly, looks good to the person who will be wearing it, then the fluorescence is simply saving you money.
Due to the slight effect that bluish fluorescence can have on yellow, you could potentially buy a diamond that appears clearer, or whiter, than it actually is. By finding a diamond with a grade of say, J, that exhibits strong fluorescence, your J could appear to be a I or even an H. This could allow you to save money, or go for a higher grade in one of the other 4 Cs.
In the end, the presence of fluorescence will cause a diamond to be given a lower cost than the same diamond without fluorescence but will in no way affect its beauty. If you are not bothered by the fluorescence, then this is a simple way to save money. Remember to always ask if the diamond is affected by the fluorescence, if it is noted on the certificate as displaying any sort of fluorescence.