The Essential
A diamond’s fluorescence is the visible glow that occurs when exposed to ultraviolet (UV) light. Fluorescence is a natural phenomenon created from the mineral properties boron and nitrogen. It can occur in many minerals and gemstones.
Diamond is crystallized carbon. This process occurs about 80-120 miles below the earth’s surface, usually where there are volcanic or ancient volcanic sites. A diamond will become fluorescent if there are traces of the mineral boron present in the earth during the crystallization process.
Almost all diamonds have some degree of fluorescence, although certain lighting conditions make this difficult to see with the naked eye. However, an ultraviolet (UV) lamp can be used to reveal a soft, fluorescent glow. Diamond fluorescence occurs in different intensities and colors. TheGIA rates the fluorescence of each diamond on a scale ranging from “None” to “Very Strong”. Fluorescence is classified as “None” when there is no visible reaction to ultraviolet light. It will be classified as “Weak”, “Medium”, “Strong” or “Very Strong” depending on how much glow is observed. According to the GIA Gem Trade Laboratory, fluorescence strength does not directly correlate with any color or clarity. In other words, it is possible for two diamonds of completely different clarity and color grades to exhibit exactly the same fluorescence power.
Diamond fluorescence scale
The images show the different levels of fluorescence on the diamonds seen from the table (top image) and from the table (bottom image).
Diamond fluorescence is graded on a scale established by the GIA. Of all diamonds sent to GIA for grading, approximately 25% to 35% show some fluorescence. Less than 1% of fluorescent diamond can affect appearance due to medium, strong or very strong fluorescence. The fluorescence is predominantly blue in glow. Sometimes, you can find diamonds with shades of green, white, pink, yellow, red, or fluorescent orange. This is very rare and can have essentially the same impact on the diamond as a blue fluorescent diamond. See scale table below for more details:
Diamond Fluorescence – GIA Study
Despite a long history of debate over the issue of fluorescence and pricing, there had been no studies examining the influence of blue fluorescence on a diamond’s appearance under normal viewing conditions until the GIA undertook their experiment in 1997.
Color evaluation in grading laboratories takes place under carefully controlled lighting and viewing conditions and primarily with the diamond positioned downwards. However, in a jewelry store or showroom, a diamond will normally be examined tableside and in a variety of lighting conditions, as is almost certainly the case when the item is worn. With this in mind, the GIA set up its experiment to study the influence of fluorescence under a range of lighting conditions and by observers inside and outside the diamond industry.
GIA found that while the effect of fluorescence on color was most noticeable in stones in the lower color grades (I and K), in the market the influence on price is greater in stones with higher color grades (D to H). This challenges the trade perception that fluorescence usually has a negative effect on better colored diamonds. They also found that, contrary to popular belief, fluorescent diamonds are not as common as non-fluorescent diamonds.
The GIA report concluded that “the diamond industry would be better served by considering each individual diamond on its own visual merits.”
Diamonrescence – Price Impacts Fluo
For an accurate summary of the effects of fluorescence on price, use the chart below. The effect on price varies depending on the diamond’s grade of color, clarity and fluorescence. For example, according to the chart, an E color diamond with VS1 clarity and strong fluorescence will tend to sell for 3-5% less than a similar diamond without fluorescence. Alternatively, a J color diamond of any clarity and average fluorescence will typically sell for up to 2% more than a similar diamond without fluorescence. While clarity has no influence on color and fluorescence appearance, it does influence price. This is because customers who gravitate towards greater clarity tend to be more averse to the presence of fluorescence:
| Color | Clarity | Fluorescence | |||
|---|---|---|---|---|---|
| Very strong | Strong | Environment | Weak | ||
| DF | IF – VVS2 | -10 up to 15% | -7 up to -10% | -3 up to -7% | -1% |
| VS1 – VS2 | -6 up to 10% | -3 up to -5% | -1 up to -2% | 0% | |
| SI1 – I3 | 0 up to -3% | 0 up to -1% | 0% | 0% | |
| GH | IF – VVS2 | -7 up to -10% | -5 up to -7% | -1 up to -3% | -1% |
| VS1 – VS2 | -3 up to -5% | -2 up to -3% | 0 up to -2% | 0% | |
| SI1 – I3 | 0% | 0% | 0% | 0% | |
| ARE | IF – I3 | 0 up to +2% | 0 up to +2% | 0 up to +2% | 0% |
While most fluorescent diamonds show a blue tone under ultraviolet light, other colors are possible. Rare yellow, orange, green and red fluorescences have been documented. These shades can increase the desire for fancy colored diamonds if they complement their primary shade. For example, a fancy yellow diamond with yellow fluorescence will have an intensity that attracts many diamond buyers, potentially raising the value of the stone.
It is important that you are satisfied with the diamond you purchase. As shown, fluorescence can greatly enhance the color and appearance of a diamond and should not be viewed unfavorably; only in exceptionally rare cases will fluorescence cause the diamond to appear milky, oily or hazy. It always comes down to a subjective decision, but best practice would be to consult a diamond specialist before purchasing to ensure you are making the right choice.