Once upon a time, there was actually a preference for stones with fluorescence. They were called “river” diamonds (found in riverbeds). They were known as “blue-white” diamonds, and there was a time when buyers insisted on diamonds with this bluish tint.

Then the standard began to change. People felt that if a diamond had extremely high color and clarity, strong blue fluorescence would cause it to appear oily, and the value should be decreased between 5-10%. The rule of thumb went even further to state that if a diamond had color and clarity that was j/k and Si1/Si2, respectfully, the diamond would “face up” better, and therefore the value should be increased up to 2%.

However, in 1997, GIA conducted a study. They concluded "For the average observer, meant to represent the jewelry buying public, no systematic effects of fluorescence were detected. Even the experienced observers did not consistently agree on the effects of fluorescence from one stone to the next.”

For the average observer, fluorescence made no difference and experienced observers (diamond graders and trade professional) could not even agree on the influence of fluorescence. And yet, the Rapaport Diamond Guide still states “For some higher-color stones, fluorescence gives the stone a milky white appearance, which greatly lowers value.”

Blue fluorescence may add value to lower-color stones as it gives the stones a whiter, brighter appearance.

So there you have it—no easy answers or consensus, even amongst the experts...