Diamond fluorescence

Diamond Education

Fluorescence in a diamond is caused by tiny boron particles ( in technical terms) which glow or emit a blue light (usually) when exposed to UV lighting. In most cases, fluorescence will not cause any noticeable effects to a diamond. However, they may actually make some lower colors (I, J, K, L, etc.) appear to be more colourless or white. In a few rare cases, diamonds with a strong or very strong fluorescence may have an increased chance of appearing milky (oily or hazy).

Even though this negative effect is relatively rare, an 8 carat diamond is a significant investment, so it is definitely worth discussing the potential effects of any fluorescence on any diamonds you are considering.

The fluorescence of a diamond is measured on a scale from None (no fluorescence), Faint, Medium, Strong and Very Strong. The strength of fluorescence in a diamond is not directly correlated to the colour or clarity of the diamond, meaning that the colour and clarity have no influence on the whether the diamond will have fluorescence or not. Diamonds of different colours and clarities can have exactly the same level of fluorescence.

  1. None (no fluorescence)
  2. Faint
  3. Medium
  4. Strong
  5. Very Strong


Diamonds with fluorescence can offer greater value for money mainly due to misconceptions about the effects of fluorescence. If the diamond is not affected in daylight (oily or hazy) then it can be a good value choice.

Under ‘normal’ lighting conditions there is no visible difference to the naked eye if a diamond possesses either None or Faint fluorescence. Under UV lighting a diamond will emit a small blue glow if it possesses Faint or Medium fluorescence, but there will still be no effect under normal lighting conditions. In some cases, diamonds that have been assessed to have Strong or Very Strong fluorescence can appear to make the diamond look milky or cloudy. This would have an impact on the beauty and sparkle of the diamond. However, each case of fluorescence should be treated individually as sometimes the affects do not necessarily have a negative effect of the diamond. Diamonds of a lower colour (I, J, K, L for example) which possess fluorescence can appear to be ‘whiter’ and more colourless.


Fluorescence can seem to be an intimidating subject when choosing a diamond, however armed with the correct knowledge it becomes clear that it’s just another factor that needs to be taken into account and is ultimately owing to personal preference and budget. Some retailers will tell you that fluorescence is bad, but many consumers actually prefer diamonds with fluorescence! The truth is that fluorescence rarely affects a diamond’s sparkle and brilliance, and in warmer or lower colored diamonds, fluorescence makes them look whiter or more colorless. Diamonds with fluorescence should be graded case by case. You may not even notice fluorescence in your diamonds, unless you are at a nightclub with black lights. Have fun and enjoy the blue glow!

About a third of diamonds exhibit fluorescence, like the fluorescent minerals you have seen in natural history museums or the novelty shop toys under the black (UV) light. The effect is like a white shirt in a discotheque. Fluorescence can be faint to very strong, and the most common fluorescent color is blue. As blue is the complimentary color to yellow, the most common tinted color in diamonds, blue fluorescence can make yellowish diamonds look white or colorless.


There are split opinions on the positives and negatives of fluorescence in diamonds. Generally, diamonds with faint or medium fluorescence cost less, as technically they are regarded as not as “pure” or as “flawless” as a diamond without fluorescence. However, in terms of value, if this has no visible affect on the appearance of the item then it may be a better choice in terms of value for money.

Since the 70’s, fluorescent diamonds have been undervalued, and can bring more positives than negatives to a diamond most of the time. Therefore, it’s important to be aware that the more fluorescence there is in a diamond, the bigger the chance the diamond will be milky. Nevertheless, even for strongly fluorescent diamonds, that chance is still remote.