Flourescence, the hidden deal-breaker in the diamond world

Most quality diamond retailers concentrate on the 4 ‘C’s of a given stone to approximate its value over the counter.  Consumers therefore are typically only aware of the Colour, Clarity, Cut and the all-important Carat when it comes to choosing a diamond, with more and more emphasis being placed these days on the 5th ‘C,’ this being the Certificate which accompanies the stone in question.

The international market price guide for loose polished diamonds, known universally as the Rappaport list, cross-references diamond pricing across the 4 ‘C’s, perhaps in a vain attempt to make life easier for the end-consumer (and indeed the retailer) to make an informed decision regarding the price of a given stone.

There is however, a further characteristic which is often ignored by both diamond-vendors and diamond-buyers, and that is fluorescence.

The 5 GIA Diamond Fluorescence grades
The 5 GIA Diamond Fluorescence grades


Various diamonds under a very telling UV lamp
Various diamonds under a very telling UV lamp

This amazing feature in a polished diamond is in fact nothing less than visible light that is generated by the stone when it is excited by ultraviolet light, i.e. sunlight.  Different diamonds react to UV excitation in different ways.  Some shine in different colours, whilst others turn whiter.  Mostly the stone exhibits a bluish hue, sometimes green, red or rarely even yellow.




Diamond Scintillation under water
Diamond Scintillation under water


Diamond lovers are sharply divided over the impact of fluorescence on the stone’s value.  There are those that believe fluorescence to detract from a diamond’s beauty by making the stone seem muddier and less brilliant, whilst others believe that fluorescence has a positive effect on yellowish diamonds, particularly as blue fluorescence acts as a counterweight to the yellow hue thus making the diamond seem whiter.

It is important to remember that all diamonds possess a degree of fluorescence, but not all of them show it off to the naked eye.  In approximately 40% of all polished diamonds, and at the atomic level, the stone’s electrons are stimulated by long-wave ultraviolet rays to the point where they re-emit the ray’s absorbed energy, and the degree of fluorescent emission is classified by the Gemological Institute of America as either Nil, Weak, Medium, Strong or Very Strong.


Whilst popular in the ‘50’s when they were termed “blue white diamonds”, visibly fluorescent diamonds are these days not nearly as expensive as their non-fluorescent counterparts as they are generally no longer in high demand.  According to secretdiamonds.com their popularity waned in the 1970’s thank to black lights that were used in discos and nightclubs.

Remember that when you are purchasing your stone, the store’s spotlights generally do not emit a sufficient quantity of UV radiation to produce the fluorescent effect.

The perfect diamond ring available from our webstore at tax-free prices
The perfect diamond ring available from our webstore at tax-free and VAT-free prices


Please visit our webstore where we shall soon be providing a comprehensive range of diamond jewellery set in beautiful 18K designer mounts.


Happy shopping.


Suresh Mahtani, The Antonio Diamond Boutique, Gibraltar.