Diamond Fluorescence

An intriguing phenomenon of some diamonds is that they appear to glow blue, and less often green, yellow, orange, or a combination of these colours when exposed to invisible ultraviolet rays. This glow is called fluorescence, and lasts only as long as the diamond is exposed to the ultraviolet rays.

In most cases, fluorescence is caused by the presence of nitrogen as a trace element impurity in diamond. You may know that diamonds are composed of carbon atoms organized in a lattice-like crystal structure. Sometimes some carbon atoms are missing in the lattice. These single or multiple vacancies may each be filled by a nitrogen atom. For example, a single nitrogen atom trapped near a vacancy causes bright orange-yellow fluorescence. But most commonly, three nitrogen atoms in lattice positions adjacent to a vacancy cause blue fluorescence.

Diamond Fluorescence

In addition to colour, fluorescence also varies by strength - from none, faint, medium, strong, and very strong, as described on GIA grading reports. The fluorescence colour and its intensity are additional characteristics that can help to identify a specific diamond.

Fluorescence is a common phenomenon in diamond. Of all the diamonds submitted to GIA over the past decade, approximately 25% to 35% exhibit some degree of fluorescence. And of those, only 10% show strengths of fluorescence in the medium, strong, or very strong categories.

GIA studies have shown that the strength of fluorescence has no widely noticeable effect on a colourless or near-colourless diamond's appearance. In fact, many prefer the appearance of diamonds that have medium to strong fluorescence. In very rare cases (fewer that 0.2% of the fluorescent diamonds submitted to GIA), some diamonds with extremely strong blue fluorescence may appear hazy or oily.

The presence of nitrogen or other impurity atoms in the diamond crystal structure does not have any influence on the hardness or durability of a diamond.

Fluorescence in Diamonds, some people like the effect while others do not, in usual circumstances it is never seen unless the diamond displays a very high fluorescence, though if a diamond that displays usual fluorescence is exposed to direct or intense ultraviolet light a bluish glow can be observed. Strong fluorescence can lower the price of a Diamond, but in some case may even lift the color one grade to the naked eye so to add to the beauty, or even detract from the diamond giving it a slightly hazy appearance. It's one factor that should be check with the individual opinion depending on the amount of fluorescence displayed.

Fluoresence in Diamonds

Listed below are the abbreviations for describing strength of fluorescence that should be noted when reading a diamond grading report:

Fluoresence in Diamonds

  • N, NO, NON, - No Fluorescence
  • F, FB, FT, FA, - Faint or Faint Blue Fluorescence
  • SL, SLB, SLT, - Slight Fluorescence
  • M, MO, ME, MD - Medium or Moderate Fluorescence
  • S, ST, STB, STG, - Strong Fluorescence
  • E, EX, EXB, EF, - Extreme Fluorescence

A contribution to understanding the effect of blue fluorescence on the appearance of diamonds

By Thomas M. Moses, Ilene M. Reinitz, Mary L. Johnson, John M. King, and James E. Shigley

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. Read full article

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