What about diamond fluorescence?
Re. fluorescence – here is some more information about what it is, how common it is and how it affects diamond price/quality.
Image courtsey of GIA
The bottom line is that Faint to Slight, and even Medium Blue has no impact on the diamond’s appearance or value. More than this (e.g. Strong on grading certificates) can have negative or positive impacts depending on what colour you are purchasing – but Strong fluorescence is only to be avoided when it makes the diamond appear ‘milkish’, like there is a fog/haze inside.
What is it? Florescence results from the interaction between a light's energy and the atoms in a diamond and makes diamonds glow in UltraViolet light (which is found in sunlight) . The most common colour for fluorescence is blue. It is not so much whether there is flourescence but the degree of fluorescence that matters. MEDIUM and STRONG fluorescence can make 'off white' diamonds appear whiter and can make white diamonds look bluer. As the best diamond colour – D is actually a “Blue white”…some decades ago, fluorescent diamonds used to be prized but since then the trend has reversed.
When a diamond has fluorescence it can be categorised into just 4 levels from None/Negligible to Very Strong (different grading labarotaries using slightly different terms but below is a generalisation):
Image courtsey of Diamond Source of Virginia, Inc
How does it happen? Diamond is crystallized carbon. If there were traces of other minerals present e.g. nitrogen, boron (these are common element) present in the earth when the this crystallization process occurred, the diamond will fluoresce. Blue is the most common colour for the fluorescence.
Do all diamonds have fluorescence? About 50-66% of the diamond have some fluorescence that can be observed under special conditions such as short wave ultra violet light. FAINT, SLIGHT or MEDIUM fluorescence has no visible impact on the diamond. 10% of the diamonds on the market have florescence that is STRONG – it is SOME of these diamonds (according to GIA, only ca. 3%) that are too be avoided as they make the diamond look milky/hazy.
How does fluorescence affect the value/quality of diamonds?
The first level of fluorescence (Faint or Slight) has ZERO impact on the value of the diamond at any colour/clarity combination as it has NEGLIGIBLE visual or other impact on the diamond.
Higher levels of Fluorescence can affect value negatively or positively depending on the quality you are looking at.
For diamonds with good colours i.e. D to H: Medium and higher levels of fluorescence commands discounts on the diamond price [because you cannot be sure if the good white colour grade awarded to a diamond is because of the fluorescence. Medium to Strong fluorescence makes any diamond face up whiter/bluer in sunlight (which contains uv).
For diamonds with colours I and below: fluorescence actually fetches a better price! This is because it makes slightly tinted white diamonds look whiter.
Here is a summary from GIA study on this subject :
"Some gem diamonds fluoresce, most commonly blue, to the concentrated long-wave ultraviolet radiation of a UV lamp. There is a perception in the trade that this fluorescence has a negative effect on the overall appearance of such a diamond. Visual observation experiments were conducted to study this relationship. Four sets of very similar round brilliant diamonds, covering the color range from colorless to faint yellow,
were selected for the different commonly encountered strengths of blue fluorescence they represented. These diamonds were then observed by trained graders, trade professionals, and average observers in various stone positions and lighting environments. For the average observer, meant to represent the jewelry buying public, no systematic effects of fluorescence were detected. Even the experienced observers did not consistently agree on the effects of fluorescence from one stone to the next. In general, the results revealed that strongly blue fluorescent diamonds were perceived to have a better color appearance when viewed table-up, with no discernible trend table-down. Most observers saw no relationship between fluorescence and transparency." For more information see http://www.gia.edu/pdfs/W97_fluoresce.pdf which is the results of GIA research on this subject.
