Fluorescence evokes words more usually associated with
psychiatric disorders. The molecules in a fluorescent diamond 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 color and clarity. When such a diamond
is placed under an ultraviolet (UV) light, however, it fluoresces, appearing to
glow with another color, 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.
Blue White
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 the 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, home of the “Big Hole” mine
pit.
One of the most famous fluorescing diamonds did come from the
Premier mine. This is the oddly named 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 Jeffrey Post, the Smithsonian’s curator in charge of its
gem and mineral collection, who gave the stone the name, claiming it had been
mined 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 fact 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 color of a diamond, particularly
when the diamond lies in the K to L color range. According to Ronnie
VanderLinden, president of Diamex and chief financial officer (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 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 color, you can get a G grade — it faces up like a G.
The UV radiation in some cases makes the stone look prettier,” VanderLinden
adds.
The Research
The Gemological Institute of America (GIA), seeking to put
the whole matter to 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 sample of 26,010 grading
reports for diamonds in the range of colorless 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
color, 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,” King says. “In the overwhelming
percent of diamonds, there is no effect on the appearance.” Both inexperienced
observers — that is, members of the consuming public — as well as members of
the trade did not discern any difference in the color 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 color — 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 different
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 colors, ‘none’ is the best. In the lower
colors, 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 color ranges. “We do value the stones differently,”
says Ehrenwald. “In a higher color, 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 these two pages). 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 a generally uniform overall appearance to the
diamonds under normal lighting conditions.” Without seeing the actual jewelry,
it isn’t possible to say whether the fluorescence gave the stones more
brilliance than their cut and clarity grades suggested, but it does prove that
one of the finest jewelry houses of our time had no problem using these
fluorescent stones in its super-high-end designs.
Article from the Rapaport Magazine - September 2011. To subscribe click here.