Diamond fluorescence buying guide

Whats is diamond fluorescence?

Diamond fluorescence refers to the effect that occurs when a diamond emits a soft coloured glow when exposed to purple ultraviolet (UV) light. Essentially the light causes natural molecules within the stone to become excited, or “fluoresce”. This fluorescence can be seen in a variety of colours, such as blue, yellow, green, or even pink. Blue is by far the most common. The intensity of fluorescence can play a part in the value of a diamond.

Photo: (Top) Maha Tannous/ GIA, (Bottom) Harold & Erica Van Pelt

Is diamond fluorescence good or bad?

Fluorescence gets a bad rap. According to a GIA study, the presence of fluorescence in a diamond is a natural characteristic that can have both positive and negative effects on the diamond's appearance. Some people preferred the look of the stones with a higher level of fluorescence. For example, a diamond with a slight blue fluorescence can make a yellowish diamond appear whiter to the eye, which can improve its overall colour appearance. Fluorescence can also have a negative effect on a diamond's appearance, depending on its intensity, but only when paired with a diamond with light scattering defects:

Does fluorescence make a diamond hazy?

“No, fluorescence does not cause haziness in diamonds. Fluorescence can increase the pre-existing haziness of a diamond caused by light-scattering defects, thus reducing the contrast in its face-up pattern, but it does not cause haziness in and of itself. As light-scattering defects are incredibly rare, most consumers don’t need to worry about fluorescence impacting a diamond’s appearance in most lighting situations, even if the diamond has Strong to Very Strong fluorescence. But this does mean that consumers should look at a diamond in person. Any haziness intensified by fluorescence, if present, will be noticeable in (for example) daylight-equivalent lighting. This hazy effect occurs in fewer than 0.2% of the fluorescent diamonds submitted to GIA.” (Gemological Institute of America (GIA), 2023)

A practical point of view.

In summary, fluorescence is invisible day to day - under intense UV light it can omit a slight, usually blueish tone. If the diamond you are selecting isn’t already hazy or milky (see diamond clarity) then it will have no visual impact on the lustre of the stone. For this reason, fluorescence is typically considered a secondary characteristic when evaluating a diamond's quality, after the 4Cs (cut, clarity, colour, and carat weight).

From an honest, practical point of view when buying diamonds, I personally don’t care about it and neither should you, its the last thing I take into consideration when assessing diamond options for a client and I wouldn't disregard an otherwise great diamond because of it having medium or strong fluorescence. I don't typically buy very strong just as a rule of thumb to avoid any potential risk of strong visual blue tones in intense light. If you are looking for perfection, stick to none or faint, if you are looking for value for money, medium or strong is fine as none is typically priced at a premium. Yes, higher fluorescence is less desirable due to its bad rap if you are trying to resell, but as per my reselling a diamond blog post, I wouldn’t take much notice of that unless you’re buying an investment diamond.