As diamond experts we are often asked the question as to whether or not diamond fluorescence is good or bad. The real answer has to be that it very much depends upon your viewpoint as the buyer of the diamond, as like all of the factors that we term the 4cs  (colour, cut, clarity and carat) it is all about individual tastes, compromise and budget. Essentially fluorescence can enhance or detract from a diamond depending upon how you view this element. This natural phenomenon is an important consideration when buying a loose diamond, so let’s take a closer look at diamond fluorescence, its advantages and disadvantages to help you choose your perfect diamond: What is diamond fluorescence and do all diamonds fluoresce?  Fluorescence is very simply the reaction of trace minerals within the diamond that cause it to emit a soft coloured glow when exposed to ultraviolet light (UV light). Diamonds contain elements such as aluminium, nitrogen, and boron and when these elements are subjected to UV light, they absorb that energy and this causes them to move to a higher energy state. In order to stay physically stable, these elements have to emit all the excess energy which they do by releasing photons or the light which is perceived as fluorescence. Not all diamonds fluoresce; in fact only about 25% to 35% of diamonds exhibit some degree of fluorescence. The most common colour seen in fluorescence is blue which applies to around 98% of all diamonds with fluorescence.  When a diamond fluoresces blue it has a tendency to appear higher in colour than its true body colour.   Also found are white, yellow, green, and even pink fluorescence. However, ultimately the colour is decided by the physical make-up of the diamond’s inner atomic structure. What are the Levels of Fluorescence? The GIA views diamond fluorescence as an identifying characteristic NOT as a grading factor like colour, clarity, cut, and carat weight are. There are however different levels of diamond fluorescence and the GIA Diamond Grading Reports and Diamond Dossiers describe a diamond’s fluorescence by its intensity - None, Faint, Medium, Strong and Very Strong (this fluorescence is in comparison to master stones used in the laboratory). Obviously, None refers to the absence of fluorescence, so the presence of this feature starts with Faint. Diamonds graded with Faint fluorescence are never hazy. This means that you can always choose a diamond with Faint fluorescence and it will not make any difference. This grade is best with a G or higher colour as it can save you money without losing the diamond’s overall brilliance. Diamonds in the level of Medium fluorescence are usually not hazy. For diamonds graded H-K in colour you should consider medium blue fluorescence. Since the glow is usually blue and blue complements yellow, diamonds with H-K colour can appear whiter. This effect will always be evident when you view your diamond under the sun as the H-coloured diamond (for example) with medium fluorescence will appear whiter than the one without fluorescence. Strong or Very Strong fluorescence will usually makes a diamond appear hazy. We would recommend that buying such a diamond is not advisable unless you can inspect it first! Diamonds within the D – F range are very prone to appearing hazy when combined with strong or very strong blue fluorescence. On rare occasions, even lower colour grades can look hazy or milky if they have Strong Blue fluorescence, although the lower the colour grade, the less likely the diamond will be to appear cloudy. Can the untrained eye tell the difference between diamonds that fluoresce and those that don’t?  The GIA undertake in depth studies into the effect of blue fluorescence on diamond appearance. They screened four sets of six diamonds, with each group representing a different colour grade (E, G, I, and K). The diamonds in each set were as similar as possible in all respects except the intensity of the blue fluorescence. Diamond graders, trained professionals, and average observers viewed the diamonds in controlled conditions to make a judgment about their appearance. The GIA found that for the untrained eye (an average observer) the average observer representing the jewellery buying public, no systematic effects of blue fluorescence on the face-up appearance of the groups of diamonds were detected. Interestingly even the experienced professional observers did not consistently agree on the effects of fluorescence from one diamond to the next. They concluded that blue fluorescence has a negligible effect on the face-up appearance of diamonds in the colourless or near-colourless grade ranges (grades D through J) with the exception of the rare instances of very strong fluorescence intensity. So is fluorescence in a diamond good or bad? As we said at the beginning for this article, diamond fluorescence is neither good nor bad as like many things in life, beauty is in the eye of the beholder. You may like it, or you may not! Let’s look at the good and bad points of diamond fluorescence: The good thing about fluorescence is that in diamonds where fluorescence does not cause any haziness, it can only be seen as a positive. One of the benefits is that most colourless (D-F) fluorescent diamonds are cheaper by 10% – 15% than a comparable gem without the blue fluorescence as for some they see this as a defect, but if you see this as part of the diamond’s natural beauty then this price drop is in fact a bonus!. If you are considering a diamond with bluish fluorescence, take the time to look at it under different kinds of lighting, including natural daylight, and compare it to other diamonds of the same colon to see if you notice any difference.  The effect of fluorescence cannot always be seen in usual lighting conditions, but once the diamond gets exposed to UV, it will shine in an icy blue way. The fluorescent effect under UV light can be pretty impressive as it can make your diamond look exceptional! Diamond fluorescence can be bad because it can sometimes cause haziness in a diamond. This would translate to milky spots that can be seen even with our bare eyes. Such gems are also referred to as “over-blue diamonds”. In addition, diamonds with blue fluorescence tend to be cheaper because of their bad reputation that is actually completely unfounded. It started some decades ago when so-called “blue white” diamonds with blue fluorescence were sold at a premium price. It was originally applied to high quality diamonds, but was later on used to market lower quality gems with blue fluorescence. This lead the American Federal Trade Commission to ban the “blue white” label. Since this time diamonds with blue fluorescence are branded with a bad name – especially by those who don't do their homework. Possibly the reason that diamond fluorescence sparks so much controversy and conversation, is because its effect is subjective and open to personal opinion. All things considered, there is no doubt that the icy-blue effect of fluorescence definitely adds to the soul of the diamond. It can only be a nuisance if your chosen diamond has a Strong Fluorescence in D-F colour or Very Strong Fluorescence in G-H colours – since they don’t have sufficient body colour to counterbalance the level of fluorescence.