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Article by Rachael Taylor

Diamonds with this trait may fetch lower prices on the market, but some in the trade are embracing the opportunities they offer.

With an inconvenient leading letter, fluorescence falls outside of the 4Cs. Yet that hasn’t stopped it from becoming an essential element when it comes to haggling the price of diamonds.

In the grading world, fluorescence refers to “the visible light some diamonds emit when they are exposed to ultraviolet rays,” according to the Gemological Institute of America (GIA). Most of the time, the light is blue, though occasionally it can be white or yellow.

Interestingly, GIA studies show that this trait has no noticeable effect on a diamond’s appearance in the vast majority of cases, although most industry buyers latch on to this diamond feature as a gateway to lower prices. The industry bible, the Rapaport Price List, has a section dedicated to the discounts one can expect for diamonds with blue fluorescence. Depending on the stone’s color and clarity, the discount can be as high as 25% if the fluorescence is very strong, or as low as 1% if it’s faint (though lower colors may have no discount at all).

Why the bad rap?

Despite the stigma, there is little science to back up claims that fluorescent diamonds are inferior stones. Fluorescence is a commonplace trait, occurring in somewhere between 25% and 35% of all diamonds, according to the GIA. Only 10% of these would have a grading classification of “medium,” “strong” or “very strong” fluorescence — the levels that the lab says “may impact appearance.”

One of the most serious — and popular — criticisms is that fluorescence can cause diamonds to look milky. Yet the GIA reports that fewer than 0.2% of the fluorescent diamonds it’s received for testing have appeared “hazy or oily” as a result of the fluorescence, so that phenomenon is incredibly rare.

A win for the budget-conscious

Though fluorescence is still an influential factor in the pricing matrix, attitudes toward these diamonds are softening as the market tries to shift away from a rigid 4Cs approach to selling — and also as tightening budgets lead trade and consumer buyers to tinker with their ideal specifications.

Not always unloved

Some buyers believe fluorescence can enhance the brilliance of white diamonds in the right color grades. Research by Venus Jewel, which specializes in manufacturing solitaires, has shown that in the top three colors — D, E and F — fluorescence enhances the stone’s luminance for a stronger sparkle.

Others in the trade report similar findings, with the GIA saying that “in many instances, observers prefer the appearance of diamonds that have medium to strong fluorescence.”

As with the 4Cs, the beauty of this much-debated “F” is in the eye of the beholder. “The overall objective needs to be achieved [through] looking at a stone and making sure it’s sparkly,” says Hanzi. “I don’t see people walking around with microscopes.” Or, indeed, UV lamps.

Facts on fluorescence

  • Up to 35% of diamonds display some level of fluorescence.
  • In more than 95% of cases, the emitted light is blue, though there are instances of other colors, such as white or yellow.
  • The GIA bases its fluorescence grades on the strength of the light the stone emits when exposed to long-wave ultraviolet rays: “none,” “faint,” “medium,” “strong” or “very strong.” If the fluorescence is medium or stronger, the grading certificate will also note the color of the fluorescence.
  • Studies show that fluorescence has no impact on a diamond’s structural integrity, and in the majority of cases, no noticeable effect on its appearance.

This is an edited version of an article first published in the April 2019 issue of Rapaport Magazine.

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