The nature of diamond

Fluorescence, a Fundamental Criterion for Diamonds

Fluorescence is not one of the 4 Cs typically cited when analyzing diamond characteristics, but it is an important factor to consider as it can greatly affect the price of a diamond.  For some diamonds it will increase the value, while for others it will be a detriment to the price.

The reaction of trace minerals within the diamond can give it fluorescence, which means that it glows in ultraviolet light (either from the sun or a black light).  About one third of all diamonds have some degree of fluorescence, which in 95% of cases is blue.  Other colors such as yellow and red are possible, but they are rare.  The Hope diamond is one such exception as it has a red fluorescence.  Laboratories assign grades of fluorescence to diamonds on the following scale: None, Faint, Medium, Strong, or Very Strong.

There is not a solid consensus on fluorescence, even among experts.  A diamond with a lower color such as J will appear to have a better color if it has blue fluorescence and may fetch a higher price than if it were not fluorescent.  Since blue and yellow are complementary colors, the fluorescent blue color makes the slightly yellow diamond appear whiter, hence the increase in price.  On the other hand, an E color diamond will lose value if it is fluorescent as it will appear somewhat murky.  Different cultures perceive fluorescence differently.  For example in the US, consumers tend to like the fluorescent glow of some diamonds, while in Asia, consumers generally do not want fluorescent diamonds.

Diamond fluorescence is sometimes considered unimportant when purchasing diamonds, but it should influence purchasing decisions if one is buying diamonds of D-F color.  While for other diamonds, the fluorescence will have little impact and may even have a positive effect on the selling price, for D, E, or F diamonds fluorescence will only reduce the gem’s value.  Consumers therefore need to exercise caution when it comes to fluorescence in colorless stones.  A large colorless diamond with a high quality rating will be hard to sell if it is strongly fluorescent.

The table below shows the price differences by color grade for fluorescent diamonds versus the same diamonds if they were not fluorescent.  For example an internally flawless (IF), G color diamond that has a very strong fluorescence would sell for 7 to 10 percent less than an internally flawless, G color, non-fluorescent stone of the same size.

Very Strong

Strong

Medium

Faint

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%