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Eric Bruton author of Diamonds discussed false white
stones in his book: “If a stone has blue fluorescence and a tinted
yellow body colour, the colours being complementary may cancel each
other so that in some conditions the stone appears white. The
experienced grader will recognize such stones because their colour
grade appears to vary in different light intensities. A white light
free of ultra-violet will disclose the true body colour, and an
ultraviolet lamp will disclose the fluorescence.”
On GIA Gem Trade Laboratory
grading reports, fluorescence is categorized by level of strength:
None, Faint, Medium, Strong, or Very Strong. When fluorescence is
faint, it’s listed without noting the colour of fluorescence wail
other levels of fluorescence are noted along with the colour.
However, GIA lists fluorescence on grading reports as an identifying
characteristic rather than a grading factor.
Fluorescence study.
The 1997 winter issue of Gems
& Gemmology presented results of a visual observation
experiment regarding fluorescence. Trained graders, trained
professionals and untrained observers viewed diamonds in various
lighting conditions and positions. They observed diamonds that
fluoresced as well as those that were inert. Not surprisingly, most
observers perceived the diamonds with strong blue fluorescence as
having better colour appearance.
The study, which also analyzed a
large sampling of data on diamonds submitted to the lab, found that
about 35% of all diamonds exhibit florescence. Of those that
fluoresced, 62% were medium to very strong and of those 97% were
blue.
Epilogue.
Consider the absurdity of
this statement: “This diamond exhibits fluorescence. That means
that in UV light such as sunlight, your diamond will look better.
Therefore I have to charge you less.” Actually, some in the trade
believe a premium is justified on lower-colour diamonds improved by
fluorescence. But if lower-colour diamonds deserve such a premium,
why don’t white diamonds that look even whiter because of
fluorescence deserve a discount?
In
The Micro World of Diamonds, John Koivula writes, “By far
the most common ultraviolet fluorescence colour in diamonds is light
blue, some-times referred to as a blue-white colour. Weak
fluorescence reactions are relatively common, but strong blue
fluorescence is much more unusual.
Courtesy JLK magazine |
