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Diamond Fluorescence

About a third of diamonds fluorescence, like the fluorescent minerals you have seen in natural history museums, or the novelty shop toys under the black (UV) light. The effect is like a white shirt in a discotheque.

Fluorescence can be faint to very strong, and the most common fluorescent color is blue. As blue is the complimentary color to yellow, the most common tinted color in diamonds, blue fluorescence can make yellowish diamonds look white or colorless.

A GIA survey found that fluorescent diamonds were favored over non fluoro stones, especially in lower colors, but even in the higher diamond colors (D, E and F) which are usually discounted by the trade. Many years ago D-F colorless fluorescent diamonds were highly prized and referred to as "blue-white". But sales people abused the term for any diamond with fluorescence; "blue-white" usage was outlawed by US trade practices laws.

One "for" argument for discounting fluorescent diamonds is because the GIA lab grading lights emit a small amount of ultra violet light; diamond fluorescence might be assigned a better color grade. 'Against' this argument (anecdotally from the GIA Gem Trade Lab) is that UV light is present in many viewing environments, so why not grade color in realistic lighting?

But the most likely reason for fluoro diamond discounting is because of the sad fact that many jewellery salespeople are not able to explain complex phenomena like fluoro; a Fluoro (or any comments) written on a report makes the diamond harder to sell = worth less! Sales killing explanation: Fluorescence is visible light emitted by electrons when a diamond is excited by higher energy source (Ultra Violet light or X-rays).

Some diamonds have extremely strong fluorescence and appear oily or cloudy like the one in the picture below. This is BAD. But the GIA study found them to be very rare; they were unable to find enough cloudy stones to do a study from the 26,010 sample they used.

Rarely diamonds fluoresce another color like yellow or orange. Do not buy them unless the diamond concerned is a fancy color of the same hue as the fluorescence (which will make it more intense). Colorless diamonds with yellow or orange fluoro will appear to be a lower color when seen in light with a UV component.

This diamond has extremely strong fluorescence in direct (left) and indirect shaded (right) cloudless mid morning sunlight.

In direct sun it has a strong milky blue cloudiness that makes the stone very dull in the left side picture.

But in the right side - even in strong lighting - the stone sparkles beautifully. The fluoro effect in some other lighting can be evident as a bluish without dulling the stones brightness or fire.

The last photo is a diamond with negligible fluoro taken in direct sunlight. Note that diamonds usually appear quite dark when seen in direct sunlight; a fact that terrify's and frightens many first time diamond buyers. Since no diamond looks really good in direct sunlight, the fact that some fluorescence diamonds get a bluish blush should not be a big deal. There are usually only very few very strong sparkles in direct sunlight, and relative darkness in the body of the diamond – and it is this effect that often shocks people the first time they see their new diamond in sunlight.

Fluorescence is not generally an issue other than also being a fun feature in its own right.

We advise you not to buy a Very Strong unless you can actually see the diamond side by side with non-fluorescent diamonds in shaded daylight (which has a lot of UV light) or with a UV filter like a small sheet of Lexan. My experience from the sales floor is confirms the GIA findings; most people would choose a fluorescent diamond over a non stone anyway. And lots of diamantaires and trade people actually seek them out. The fact it may cost less is a real bonus.

When the UV light is turned off, fluorescence ceases instantly, but some stones continue to phosphoresce for a little while.

See also "Calling all who have SEEN a strong blue fluor diamond".

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