Diamond Lessons

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)
• Faint
• Medium
• Strong
• 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.

One of the determinants of the color of a diamond is dependent on the particular characteristics of the trapped foreign objects. In the case of the aforementioned nitrogen (N), the trapped nitrogen atoms, if in large, even-numbered aggregates greater than pairs, will absorb the wavelengths of light that produce a light yellow or brown color. These diamonds that hold nitrogen as their primary impurity fall into the category of Type I diamonds, which make up 98% of all diamonds. The color blue is produced as a result of the presence of the elements boron (B) or hydrogen (H), as these colors absorb the light wavelengths that produce the color blue. Diamonds with boron as their impurity fall into the category of Type II diamonds.

It may appear that all diamonds are alike, at least in their basic make-up; however, it is important to be aware that there are some notable differences within diamonds at the atomic level. This main distinction is made between diamonds that contain nitrogen and those diamonds that do not contain nitrogen. This is illustrated in the splitting of diamonds into two main diamond categories: Type I and Type II. These two categories are differentiated on the atomic level, and so certain tools, such as a spectrograph (a device that measures the amount of infrared light that is absorbed by the diamond) are required even by an experienced graduate gemologist to place them within a Type category.

Type I Diamonds

In the 1930's it was discovered that about 98%-99% of all found diamonds contained nitrogen (N) as their primary impurity. This nitrogen is detected using a spectroscope, as the nitrogen absorbs infrared light. This impurity usually occurs in one of two ways, either in large groups (aggregates), of nitrogen, or as single nitrogen atoms scattered within the diamond's crystal lattice. These two forms of impurity are further broken down into two sub-groups: Type Ia and Ib.

Type Ia diamonds are those diamonds that contain nitrogen in aggregates. When these aggregates occur in pairs within the diamond lattice (A aggregates) or as aggregates of four (4) nitrogen atoms (B aggregates) they do not absorb any of the wavelengths of visible light. When nitrogen occurs in groupings of three (known as N3 center) however, the nitrogen groups absorb the visible light within the blue end of the spectrum, causing a yellowish color to appear in the diamond. This means that the nitrogen in Type IaA-aggregate and IaB-aggregate diamonds does not affect a diamond's color, whereas the nitrogen of Type IaN3 center does affect the diamond's color, saturating it with the yellowish tint we are familiar with.

Type Ib diamonds are far less common than Ia, occurring in less than .1% of all naturally occurring diamonds. Type Ib diamonds are diamonds that contain single nitrogen atoms scattered throughout the diamond's crystal lattice framework. It is this scattering of single nitrogen atoms, allowing the absorption of visible light in the blue end of the spectrum that gives rise to the intense yellow color found in the true Canary yellow diamonds (rare and valuable Fancy colored diamonds). This atomic formation can also give rise to browns and yellowish -green diamonds.

Type II Diamonds

In Type II diamonds, there is no sign of nitrogen present when viewing the diamond's light properties on infrared light with a spectroscope, as there is little absorption of infrared light occurring within these diamonds. This does not mean that absolutely no nitrogen atoms are present within the diamond's crystal lattice. The spectroscope's resultant findings simply indicate that nitrogen does not appear in a large enough quantity to have any affect on the diamond's optical properties. Type II diamonds are also split into two categories, Type IIa and Type IIb. These sub-groups are separated with Type IIa diamonds not capable of conducting electricity and Type IIb diamonds that are able to conduct electricity.

Type IIa diamonds are colorless, unless they have an inclusion or defect in the crystalline structure that would allow light absorption to occur. Diamonds of this type can be gray- brown, yellow, pink, light blue, or light green (with these two last arising from radiation exposure), but more often these are the perfectly colorless diamonds that most people are looking for. This is due to the fact that their structure does not easily absorb short-wave ultraviolet light wavelengths, but instead allows the light to pass through. Such famous diamonds as the Cullinan (the world's largest cut diamond, found in the South African Premier Mine in 1905) and the Koh-i-Noor (Urdu for "Mountain of Light"), which was found in India and now rests in the Tower of London, are type IIa diamonds.

Type IIb are diamonds that are electrically conductive, and the most distinguishing feature is the presence of boron (B) in this type. Boron is not present in Type IIa diamonds, and serves as the primary difference between the sub-groups. The presence of boron within this diamond type causes almost all of them to be either blue or bluish gray. Boron, as a foreign element in Type IIb diamonds, provides the blue color due to the boron's absorption of light towards the red end of light's color spectrum.

The color of "fancy" diamonds comes from the mineral elements found in the individual diamond, such as chromium, magnesium, cobalt, titanium, iron, vanadium, nickel and copper. The pink color of some diamonds, as well as the rare green, often get their color not from trace elements, as with the other colored diamonds, but from radiation and temperatures acting during the diamond's formation. "Fancy" diamonds are some of the best known and famous. One of the most famous diamonds, the dark grayish-blue, 45.52 carat Hope Diamond, is also one of the most sought after, and costly, of all diamonds.

All fancy color grading must be made under a prescribed set of conditions. These conditions include: viewing the diamonds under a 10x loupe by three trained gemologist; viewing the diamond in a diamond box (which provides a white background and white surroundings); viewing the diamond through the table, pavilion down; and viewing the diamond from multiple angles, still with the pavilion down.

The GIA Fancy Colored Grading Scale

GIA does not grade fancy colored diamonds on the colorless diamond color-grading scale. They instead use a scale that rates the diamond's color on three primary characteristics: Hue, Tone and Saturation.

Hue

The Hue in color grading refers to the primary and notable colors that are present in the diamond, such as Pink, Blue, Yellow, Brownish-Yellow, and so on. GIA recognizes 27 hues in grading fancy colored diamonds.

Tone

The Tone of color grading refers to the lightness or darkness of the hue, or primary color of the diamond.

Saturation

Saturation is the measure of how strong and intense the primary color of the diamond actually is, such as light, deep, intense or vivid.

The 9-grade GIA color grading scale runs as follows:

• Faint
• Very Light
• Light
• Fancy Light
• Fancy
• Fancy Dark
• Fancy Deep
• Fancy Intense
• Fancy Vivid

This grading scale measures how the level of color saturation is found in a given fancy colored diamond. It is also important to note that when a fancy colored stone is being graded it is viewed from the top down, as opposed to the normal grading method for colorless diamonds (which are looked at with the bottom, or pavilion up and the top, or table, down).

In recent years fancy colored diamonds have gone from being interesting oddities and curio pieces to being immensely sought after and greatly desired gems in their own right. Many of the world's most famous diamonds (such as the South African mined 128.54 carat, canary-yellow Tiffany diamond, brought out in 1877) have been fancy colored diamonds. This mixture of history and celebrity has only increased the current desire for fancy color diamonds.

The very color of fancy colored diamonds also makes them more difficult to cut properly. Fancy colored diamonds have their own demands for the diamond cutter, in that the diamond cutter is not cutting to produce the same effect that is sought after in colorless diamonds. In the case of fancy colored diamonds, the main goal of the diamond cutter is to preserve and enhance as much of the natural color of the diamond as is possible. Therefore, it is to this end that the cutter must strive to facet and polish the diamond to facilitate the entering light to produce the most vivid display of the diamond's color. In the end, the goal in cutting a fancy colored diamond is not to produce maximum scintillation or fire, although these are desired, but to bring out the most color. The very nature of the fancy colored diamonds preclude them from being particularly exceptional in brilliance and fire, as many wavelengths of the entering light are being absorbed by the diamond's color producing agent, whether this be foreign matter, irregular crystal growth or radiation.