Diamond Rings

Diamond Fluorescence

December 30th, 2005

Around two thirds of diamonds fluoresce to some extent under both artificial, and natural ultra violet or UV light. The bright rich purple type of lamp found in sun bed and pubs/clubs, is a typical artificial UV source. Sun light is of course a natural source of ultra violet light, and most diamonds that flouresce srongly will take on a bluish tint. This phenomena has consequences for colour grading because a strongly fluorescing diamond will appear to have a different colour when viewed in strong sunlight than it does when viewed under artificial light in your home.When blue flourescence is observed in colourless diamonds these diamonds are additionally described as JAGER, indicacating their property of fluorescence. Jager (from the South African Jagerfontein mine) is not to be confused with an old term for describing the best white diamonds. The Jager or ‘blue white’ colour, it was realised, was in fact a ‘D’ colour diamond which exhibited fluorescence and hence Jager is no longer used in this respect.

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’.

Entry Filed under: Diamonds