Diamond Fluorescence

Fluorescence

Around two thirds of diamonds fluoresce to some extent under both artificial, and natural ultra violet (UV) light. Most diamonds that flouresce srongly will take on a bluish tint. This phenomena has consequences for colour grading because a strongly fluorescing diamond may appear to have a different colour when viewed in strong sunlight than it does when viewed under artificial light in your home.

Simple UV Lamp for viewing Fluorescence with Long and short wavelength UV

Diamonds with a slight yellow tint when mixed with the bluish glow from fluorescence may appear a better colour, or less yellow, than they are in artificial light. Colour grading is therefore performed under an ultra violet free source and then graded for fluorescence separately. We use white light of colour temperature between 5000/5500 Kelvin to colour grade. To examine fluorescence we use two forms of artificial UV light, mostly long wave UV (LWUV) producing radiation at 365nm and Short Wave (SWUV) radiation at 254nm (nm=nanometre or 0.000000001 metre). Most fluorescent diamonds are excited by long wave UV and just a few at shorter wavelengths.

In the GIA system two comparison Master stones are used and these are located at the borders between faint/medium and medium/strong. This permits five grades: NONE, FAINT, MEDIUM, STRONG and VERY STRONG. The strength is a direct comparison with the two master stones. Fluorescence is not always a good thing though. A few diamonds exhibit a yellow fluorescent glow which will make the diamond appear to be a colour grade worse in UV rich sunlight. Extremely fluorescent tinted diamonds exhibit a milky-bluish or petrol-coloured effect and are often termed 'over-blue'.

Fluorescence: Influence on price

The nature of blue fluorescence on price is dependent on its visual impact. For higher colour stones D,E, strong fluorescence causes a detrimental milky effect which lowers the value, see table below. However at the other end of the scale with lower coloured stones I,J,K, strong fluorescence is desirable and will attract a premium.

Colour Fluorescence IF-VVS VS SI-I3

D E Very Strong -10% to -15% -6% to -10% 0 to -3%

Strong -7% to -10% -3% to -5% 0 to -1%

Medium -3% to -7% -1% to 2% 0

Weak 0 0 0

F G H Very Strong -7% to -10% -3% to -5% 0

Strong -5% to -7% -2% to -3% 0

Medium -1% to -3% 0 to -2% 0

Weak 0 0 0

I J K Very Strong 0 to 3% 0 to 3% 0 to 3%

Strong 0 to 2% 0 to 2% 0 to 3%

Medium 0 to 2% 0 to 2% 0 to 2%

Weak 0 0 0


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Colour	Fluorescence	IF-VVS	VS	SI-I3
D E	Very Strong	-10% to -15%	-6% to -10%	0 to -3%
	Strong	-7% to -10%	-3% to -5%	0 to -1%
	Medium	-3% to -7%	-1% to 2%	0
	Weak	0	0	0
F G H	Very Strong	-7% to -10%	-3% to -5%	0
	Strong	-5% to -7%	-2% to -3%	0
	Medium	-1% to -3%	0 to -2%	0
	Weak	0	0	0
I J K	Very Strong	0 to 3%	0 to 3%	0 to 3%
	Strong	0 to 2%	0 to 2%	0 to 3%
	Medium	0 to 2%	0 to 2%	0 to 2%
	Weak	0	0	0