Fluorescence refers to a diamond’s tendency to emit a soft coloured glow when subjected to ultraviolet light (such as a “black light”). This is due to sub-microscopic structures within florescent diamonds. Roughly 30% of diamonds fluoresce to some degree. Colourless (D-F) Very Strong fluorescent diamonds sell at up to a 10% discount since the fluorescence is perceived as a defect. In fact, the visible effects of Faint to Medium fluorescence are perceptible only to a gemmologist using a special UV light source.
Fluorescent glow is most commonly blue. However, other colours can occur, such as orange, green, and yellow. Because the fluorescent glow is usually blue (which is the complementary colour to yellow) fluorescence can make diamonds of I-M colour appear up to one grade whiter. For this reason, I-M diamonds tend to sell at a slight premium when they possess Medium to Very Strong fluorescence.
A GIA study of diamond fluorescence:
A study performed in 1997 by the GIA found that the level of fluorescence has no widely perceptible effect on the colour appearance or transparency of diamonds when viewed table down (upside down). In the table up position, diamonds of Strong or Very Strong fluorescence appeared to have better colour than less fluorescent stones. The effect was most noticeable in the I-K colours.
Top Row: Diamonds with 5 degrees of fluoro,
Bottom Row: Same diamonds under UV light,
ordered from Very Strong to No fluoro.
Overall, diamond fluorescence should not be a major factor in the purchase of a diamond since its effects are negligible, if not slightly positive. The exception would be to exercise caution in purchasing a diamond with Strong Fluorescence in D-F colour diamonds or Very Strong Fluorescence in G-H colour diamonds (which do not possess enough body colour to offset the degree of fluorescence).
Every Diamond displays the fluorescence grade as determined by the GIA, using the following scale:
Very Strong, Strong, Medium, Faint, None
For a precise summary of the effects of fluorescence on price, use the chart below. The effect on price varies depending on the degree of fluorescence, diamond colour, and clarity. For example, according to the chart an E colour diamond of VS1 clarity and Strong Fluorescence will tend to sell for 3-5% less than a like diamond with no fluorescence. Alternatively, a J colour diamond of any clarity and Medium Fluorescence will typically sell for up to 2% more than a like diamond with no fluorescence. While clarity has no bearing on the appearance of colour and fluorescence, it does impact price. This is because customers who gravitate towards higher clarity tend to be more adverse to the presence of fluorescence.
HOW FLUORESCENCE AFFECTS PRICE
|D – F||IF – VVS2||-10 to -15%||-7 to -10%||-3 to -7%||-1%|
|VS1 – VS2||-6 to -10%||-3 to -5%||-1 to -2%||0%|
|SI1 – I3||0 to -3%||0 to -1%||0%||0%|
|G – H||IF – VVS2||-7 to -10%||-5 to -7%||-1 to -3%||-1%|
|VS1 – VS2||-3 to -5%||-2 to -3%||0 to -2%||0%|
|SI1 – I3||0%||0%||0%||0%|
|I – M||IF – I3||0 to +2%||0 to +2%||0 to +2%||0%|
Overall, a fluorescent diamond can present you with an opportunity to save money when making a purchase. There is nothing wrong with going down this route provided the quality of the chosen diamond is not compromised. In rare instances a florescent stone can result in the overall look of a diamond appearing milky or cloudy. This should be avoided at all costs.