........An estimated one-quarter to one-third of all diamonds exhibit fluorescence and yet it remains somewhat contentious.
By Ettagale Blauer
Fluorescence evokes words more usually associated with psychiatric disorders. The molecules in a fluorescent diamonds are said to be unstable, excited and structurally defective. That’s a heavy burden for a beautiful gemstone. These terms all relate to the presence of nitrogen-related defects, which lead to fluorescence. When a fluorescent diamond is viewed in ordinary light, it shows its normal qualities of colour and clarity. When such a diamond is placed under an ultraviolet (UV) light, however, it fluoresces, appearing to glow with another colour, most commonly blue. Since this quality disappears once the diamond is returned to a natural light source and ‘relaxes’, the fluorescence is a temporary condition. However, fluorescence‘s ultimate ability to permanently affect the overall appearance of the stone under normal lighting conditions is the issue that arises when diamonds are priced.
In the early days of diamond trading, especially after diamonds were discovered in South Africa, diamonds that showed a fluorescent quality were highly prized and were described as “blue white”, The suggestion of a blue tint, though not actually visible to the unaided eye, gives many diamonds added brilliance. This is a commonly accepted fact both in the trade and in the laboratories. Conflating the good and bad, such diamonds were said to be “Premierish”, meaning that they were like the genuinely blue diamonds that were produced by the renowned Premier mine, although diamonds with fluorescence can be found in any mine, whatever the location. The term remains in casual use today, just as diamond-bearing pipes around the world are called kimberlites, after the town of Kimberley, hoe of the “Big Hole” mine pit.
One of the most famous fluorescing diamonds did come from the Premier mine. This is the oddly name Portuguese Diamond, a 127.01-carat step-cut octagonal stone with extremely strong blue fluorescence, a quality known in the trade as ”overblue”. This depth of fluorescence gives the stone an oily or hazy appearance, making it far less attractive or desirable. The Smithsonian Institution in Washington, D.C., acquired the Portuguese Diamond from Harry Winston in trade for a couple of thousand smaller diamonds. It was Winston, according to Jeffery Post, the Smithsonian’s curator in charge of its gem and mineral collection who gave the stone the name, claiming it had been minded in Brazil and had been owned by the Portuguese royal family. As Post put it in an interview in Smithsonian Magazine, “We know now that this stone has never been to Portugal, has never been to Brazil, but in face came out of the Premier Mine”.
Its overblue quality did nothing to enhance the Portuguese Diamond’s beauty. In lesser intensities, however, blue fluorescence often improves the colour of a diamond, particularly when the diamond lies in the K to L colour range. According to Ronnie VanderLinden, president of Diamex and chief financial offer (CFO) of the Diamond Manufacturers & Importers Association (DMIA), “It does not matter if a diamond is fluorescent – unless it’s overblue. Overblue will affect the price of the diamond – if it’s hazy, oily, or Premierish, it affects the brilliance.” On the plus side, he says, “A lot of the medium and stronger blue fluorescent stones can have a crispy look; it absolutely helps the diamond. It gives a beautiful brilliance. Fluorescence is a part of nature; there’s no reason to downplay it.” In spite of this benefit, he adds “You don’t pay more for these stones.” In some instances, the improvement from fluorescence is considerable. “For an H colour, you can get a G grade – it faces up like a G. The UV radiation in some cases makes the stone look prettier,” VinderLinden adds.
The Gemological Institute of America (GIA), seeking to put the whole matter to a rest, embarked on a massive comparison of diamonds with and without fluorescence. The results were exhaustively detailed in an article in Gem & Gemology’s Winter 1997 issue entitled “A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds.”
The mammoth study involved a random sampled of 26,010 grading reports for diamonds in the range of colourless to faint yellow. According to the article, “The data revealed that approximately 65 percent of these diamonds had no reported fluorescence to long-wave UV radiation.” Further, of the 35 percent of diamonds that showed fluorescence – 9,175 diamonds – 38 percent showed faint fluorescence and 62 percent had medium to very strong fluorescence. Of these 5,710 diamonds with medium to very strong fluorescence, nearly all fluoresced blue. Only 3 percent, or 162 stones, showed another colour such as yellow, white or orange.
John King and Tom Moses, two of that study’s authors, discussed the quality of fluorescence as investigated by GIA. “You don’t see the quality of fluorescence with the eye, there is no effect on the appearance.” Both inexperienced observers – that is, members of the consuming public – as well as member of the trade did not discern any difference in the colour appearance or transparency of stones with and without fluorescence by eye. “You might see it under a loupe,” Moses says.
The negative reputation of fluorescence, King says, grew out of the awareness of stones such as the Portuguese Diamond. “Stones like that – overblues – give fluorescent stones a bad reputation.” He adds, “Diamonds with fluorescence that had poor colour – I to L – looked better because they had fluorescence. Fluorescence has less of a visual effect in D to G diamonds. Beauty should be in the eye of the beholder,” but sometimes the market takes over when the eye should rule. “Sometimes dealers just need to create difference price points” when fluorescence is present, King says. Moses adds, “The dealers have devalued the price of those diamonds by talking them down. This will eventually correct itself; supply will be less than demand.”
Certifying for Fluorescence
Fluorescence is noted on diamond grading reports according to the intensity of the quality. Jerry Ehrenwald, president of the International Gemological Institute (IGI), says, “We follow the same process as GIA. We report fluorescence as ‘none’, ‘faint’, ‘moderate’, ‘strong’, ‘very strong’.” Ehrenwald agrees that “In the higher colours, ‘none’ is best. In the lower colours, K to L, fluorescence helps the diamond. It can be a positive attribute; it adds a little brightness.”
IGI’s appraisal division also evaluates fluorescence differently for different colour ranges. “We do value the stones differently,” says Ehrenwald. “In a higher colour, a strong blue would be a negative and we would deduct about 5 percent. There would be no deduction for faint or medium blue.” There’s no added value for K to L stones that have fluorescence and there is only a “very slight deduction” for a strong blue in this range. “The one negative about fluorescence is when the diamond shows that gray, hazy, Premierish look.”
Perhaps the most intriguing, and revealing, example of fluorescence in diamonds may be seen in two photographs of a Harry Winston necklace and earrings shown in the Gem & Gemology article and on that issue’s cover (see photos on this page). On the left, classic Harry Winston designs comprising numerous fancy shape diamonds are seen under normal lighting conditions. Shown on the right, as seen under a long-wave UV lamp, nearly all the stones in the same necklace and earrings display blue fluorescence, while at least two of the stones display yellow fluorescence. Only a few of the diamonds appear to have little or no fluorescence. The article notes that despite the range of fluorescence strengths in the individual diamonds, “there is generally uniform overall appearance to the diamonds under normal lighting conditions.” Without seeing the actual jewellery, it isn’t possible to say whether the fluorescence gave the stones more brilliance that their cut and clarity grades suggested, but it does prove that one of the finest jewellery houses of our time had no problem using these fluorescent stones in its super-high-end designs.
Blauer, E, 2011. Blue Glow. Rapaort, 34/9, 83,84,85.