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Diamond Fluorescence-What’s the Story?

You probably discovered some dealers make a big thing of the blue fluorescence which diamonds exhibit under UltraViolet light.


In the past, the 4 C’s – Carat, Cut, Clarity and Colour – were used to describe the rarity of a polished diamond and to determine its value. However, it was never intended to be the whole story as diamond experts preferred to value a stone on its size, beauty and sparkle. But, when dealer price lists became available to the public and everyone wanted to buy at or below the list price, profit margins shrunk drastically. Dealers thus looked for reasons why two similar looking diamonds should differ in price.

The fact that some diamonds glow blue or yellowish under ultra-violet light while others not, provided a reason. And today, a white diamond with strong blue fluorescence is priced at 10-25% below a similar diamond that shows no fluorescence. Because, dealers explain, the blue glow may cause a diamond to look whiter than what its true body colour is and the colour grade on the grading report thus too high, therefore the discount.


  • At the beginning of the 20th century, colorless diamonds with blue fluorescence were the most prized. They were called “blue white” and fetched huge premiums. Did dealers in those days know something that we today do not?
  • In 1997, Dr Tom Moses, chief researcher of GIA, published a landmark study: “A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds.”   While fluorescence can cause a cloudy appearance in some diamonds, it is neither the strength of the fluorescence nor body color of the diamond that determines the effect. It is the transparency of the crystal. Gem-quality diamonds with high transparency look brighter and whiter under the influence of fluorescence, while diamonds with inherently poor transparency look hazier.”
  • He concluded: “the present study challenges the trade perception that the fluorescence usually has a negative effect on better-color diamonds. Our results show that the diamond industry would be better served by considering each diamond on its own visual merits.”
  • GIA found that for probably 80% of the time, blue fluorescence improves the overall appearance of diamonds.
  • Unfortunately, the majority of online sellers would have you believe that blue fluorescence always causes a hazy or oily appearance in a diamond and that you need to deduct value from any diamond if its fluorescence is strong. This is a fallacy.

 OUR ADVICE:   You need to see the stone in person, not rely on what is written on a diamond report or look at a photograph on a dealer’s website. Most of the time blue fluorescence improves the look of a diamond, but, in certain cases, it will degrade the stone and justify a discount. Which is why you should visit us and let us show you when fluorescence affects the beauty of a diamond.

If not possible to see us personally, the expertise and integrity of our gemmologists will guide and advise you.

Fluorescent natural diamonds are a wonder of nature and usually outshine their inert counterparts.

PLEASE NOTE: Synthetic diamonds do not exhibit blue fluorescence under UV light. If your diamond glows magically at the nightclub and sparkles magnificently in the sunlight, then you know it’s natural.

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