Reading Diamond Certs :: Fluorescence

Diamonds have many unique properties, including natural blue Fluorescence (and other colors rarely) under a source of ultraviolet light.

One technique that gemologists use to help identify and separate diamonds from the diamond look-alikes (such as moissannite and cubic zirconia) is by putting the gem under a UV lamp. If it fluoresces (glows) blue, it is almost certainly a diamond. In fact, most diamonds have some degree of fluorescence under UV light.

How does fluorescence effect the beauty or value of a diamond? The answer to that question is complex, and primarily depends on the color grade of the diamond you are buying.

How fluorescence affects beauty ::

Recent studies by GIA have shown that…

Fluorescence in any amount does not impact the face up appearance of a diamond. [Note from Robert :: except possibly those with Extremely Strong fluorescence].

Here is my take on fluorescence… the rest of the story.

If a diamond has a color grade of J to M or so, a moderate to strong amount of blue fluorescence could actually make a diamond more attractive to most people. It could actually help cancel some of the yellow and make it looks whiter to the eye under normal conditions in the sun or your living room.

For a diamond with very high color (such as a D to F grade), fluorescence is thought by some older dealers to interfere with the flow of light and make the diamond appear a little oily or murky. This will not be true for most diamonds, but it is still a common belief.

Personally, I do still feel a little hesitant to recommend D to F color diamonds with Very Strong to Extremely Strong fluorescence, despite the recent research. This is just because of my own habit of thinking and many years of training that we should avoid them. For this reason, I still might recommend None, Slight, or Moderate flourescence in colorless diamonds (D to F color grades).

How fluorescence affects price ::

Therefore, the prevalent belief of the older dealers in the trade, and the prevalent belief among consumers educated by those dealers, causes less demand for stones with fluorescence. This brings the price down, sometimes by quite a lot, because they are harder to sell. This makes them great deals.

If you are looking for a great deal on a diamond, I sometimes RECOMMEND fluorescence.

Conclusion / My Advice ::

In color grades from D,E,F color — be a little careful with Very Strong to Extremely Strong fluorescence. It may or may not affect beauty, but it will lower the price.

In color grades from G,H,I — it might be better to stay away from Very Strong to Extremely Strong fluorescence for safety’s sake, but Slight to Strong blue fluorescence will not hurt you, and might give you a better deal.

In color grades from J,K,L,M — it might be a great thing for both looks and value to go with blue fluorescence from Slight to Strong blue. I still tend to avoid Very Strong to Extremely Strong fluorescence, even for these colors, just in case!


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