Fluorescence is the tendency of a diamond to emit a soft glow when the stone is exposed to ultraviolet light (UV light). Fluorescence is neither good or bad, but definitely something to consider as it can improve a diamond’s color or make the gem look hazy. The fluorescence effect is present in over 30% of diamonds so there’s a good chance you’ll encounter it especially when buying a loose diamond.
What is Diamond Fluorescence?
Fluorescence is one of the most misunderstood attributes of a diamond. Fluorescence is simply the stone’s reaction to UV light (sunlight or black light) and comes from the inclusion of trace elements naturally contained within a diamond during the carbon crystallization process. A significant percentage of stones on the market have some degree of fluorescence; the vast majority of those are blue but in rare cases white, yellow, orange and red fluorescence is also seen.
In most cases fluorescence is simply an identifying characteristic of a diamond and not a performance characteristic, so therefore it is neither good nor bad. The GIA grades fluorescence in diamonds as None, Faint, Medium, Strong and Very Strong. Depending on the diamond, fluorescence can either improve the diamond’s color or make it appear oily, hazy or milky.
- None: diamonds with no fluorescence present
- Faint: a slight amount of very subtle blue hue under UV light, usually not detectable to the unaided eye
- Medium: a stronger blue glow under UV light usually not detectable to the unaided eye, but can cause a diamond to appear slightly, cloudy, milky, or hazy to the naked eye
- Strong: a substantial and intense blue hue under UV light which can cause a diamond to appear very cloudy, milky, or hazy to the naked eye
- Very Strong: a prominent and saturated blue hue under UV light and can cause a diamond to appear substantially very cloudy, milky, or hazy, to the naked eye
When diamonds have slight or faint fluorescence, they don’t appear cloudy, in fact the slight fluorescence can make the diamond appear more white. When fluorescence makes the diamond hazy, the stone is less transparent so light won’t reflect as well and the diamond won’t be as clear or beautiful.
Does Diamond Fluorescence Matter?
Fluorescence doesn’t impact a diamond’s internal structure or texture, it isn’t harmful to the diamond and can’t damage it, it’s simply a combination of different minerals that interact with UV light. Although fluorescence doesn’t change a diamond, it can affect how an observer perceives it in some cases which can also impact its price. Diamonds come in shades of white and yellow and fluorescence can enhance or detract from the beauty of a diamond.
The bluish tint from fluorescence can improve a lower-color diamond (J-M color rated) by canceling out the faint yellow, resulting in a more colorless white appearance. The same applies the opposite way around, fluorescent diamonds in the colorless and near-colorless range (D-F) will look bluish under UV light and can also look hazy or oily in appearance.
Sometimes, a diamond’s fluorescence will have no effect on its price, other times it will. Colorless stones, those with a color grade of D-F, are sometimes sold at a discount because the fluorescence is seen as a flaw, but those with a color grade of I-M are actually sold at a premium because the fluorescent glow compliments the yellow undertones of a colored diamond.