Diamond Fluorescence

By 20.06 September 20th, 2018 No Comments

 When wanting to buy a diamond, perhaps to extend a diamond collection, a buyer most likely would be looking for the largest and best stone available at the lowest cost. The 4Cs are the points to be taken into consideration, but in some stones there are features which are invisible to the naked eye. Among other features, the overall value of a stone may be reduced by the presence of fluorescence, which will not significantly reduce the quality of the actual diamond. Liaise with a trusted gemologist when reviewing stones so that you can physically see the stones before committing to payment. Fluorescence is really a matter of individual preferences but always check the certificate!

Fluorescence is a soft coloured glow emitted by a diamond when exposed to electro-magnetic radiation in the form of ultra-violet light rays. The source of UV radiation can be from black lighting in night clubs, fluorescent light bulbs and also natural sunlight. Exposure will show a glow due to the presence of boron, nitrogen or aluminum, stimulated by ultra-violet light rays in the stone’s atomic structure. These electrons absorb energy, become ‘excited’ and jump to higher energy states. The Law of Physics states that ‘excited’ electrons seek to return to stability. To do this they emit the excess energy in the form of photons and this photon release is what is seen as fluorescence.

This glow, caused by the reaction of trace minerals within the diamond, may enhance a diamond’s appearance in many stones. Approximately 30% of colourless diamonds (D-F) show fluorescence to some degree, and as fluorescence can be perceived as a defect, these stones are sold at a discount of up to 15%. However, this glow may cause diamonds in the I-M colour range to seem to be one grade whiter. Thus if stones have a fluorescence of Medium to Very Strong they may sell at a slightly higher price, while the price of those with Faint to Medium fluorescence is not significantly affected.  Sometimes exceptional diamonds are unnecessarily avoided due the presence of fluorescence in them. The beauty of a diamond is mostly determined by its cut, and fluorescence may or may not affect the stone in any perceptible way.

Very Strong Green Fluorescence

Very Strong Green Fluorescence

Very Strong white Fluorescence

Strong White Fluorescence

In Fancy Colour Diamonds fluorescence can appear in a number of different shades or colours such as blue, yellow, white, orange, green, and pink, whereas in colourless diamonds, it will generally appear only in a yellow or blue tint.

Generally consumers who choose carefully are not likely to see the presence of fluorescence,
as this does not affect the general appearance of a stone, and most diamonds with fluorescence will have as much brilliance as those with no fluorescence. Also a hazy, milky, oily appearance may also be seen in stones with no fluorescence; perhaps these stones should not be considered for purchasing.

The colour of fluorescence is generally in the blue range (complementary colour to yellow) but it can be seen in other colours; this has the tendency for the colour to seem higher than the true body colour and near colourless stones can look colourless to the naked eye. Yellow and white are also common but other colours such as green, pink and red are usually rare.  Strongly blue coloured fluorescence is perceived to have a higher grade than the actual colour grade of the diamond as the stone looks whiter, and this is often found in the D-E grades. Fluorescence of a yellow colour may be a negative factor.


The GIA scale uses the following grades to identify fluorescence:

None, Nil, Negligible: no fluorescence, no influence on colour
Faint, Slight: weak fluorescence, not a significant influence on colour (barely perceptible
Medium: average fluorescence, small influence
Strong, Extremely Strong: strong fluorescence, substantial colour influence.

When purchasing diamonds, fluorescence can work to the buyer’s advantage with a 4-10% discount on the price, depending on the fluorescent strength. Always ensure that there is an option to return a diamond with fluorescence although the average consumer will probably not be affected by the connection of fluorescence and clarity of a particular stone. Check a stone’s fluorescence with the dealer and avoid buying a stone with extremes of fluorescence in terms of strength. The average diamond wearer will not notice the effect of fluorescence. 

Fancy Colour Diamond Fluorescence 

fancy coloured diamond flouressence

The colours of the diamonds shown are from left to right: Fancy Deep Brownish Yellow, Fancy Vivid Yellow Orange, Fancy Vivid Yellow Orange, Fancy Deep Grayish Yellowish Green/Chameleon, Fancy Dark Gray Yellowish Green/Chameleon, Fancy Intense Yellow, Fancy Pink, Fancy Greenish Yellow, Fancy Intense Green Yellow, Fancy Intense Green Yellow.


Blue is by far the most common fluorescence colour in diamonds when they are exposed to longwave UV rays. Copyright: GIA and Harold & Erica Van Pelt. Courtesy: Harry Winston, Inc.


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