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Diamond Fluorescence 


Diamonds remain amongst the most precious and admired gemstones in the world. Most people appreciate their mesmerising sparkle, but did you know that some diamonds glow under UV light? We refer to this phenomenon as diamond fluorescence—a fascinating characteristic exhibited by only some diamonds. Our information includes some. helpful information on buying fluorescent diamonds or for just learning a little more about the subject. 

Two diamonds compared. Left - a non-fluorescent diamond next to an ideal cut diamond with fluorescence. 

What is diamond fluorescence?


Fluorescence is the emission of electromagnetic radiation (including visible light, ultraviolet light, X-rays, and gamma rays) from a substance stimulated by the absorption of incident electromagnetic radiation.


Diamond fluorescence describes the ability of a diamond to emit a soft glow when exposed to ultraviolet (UV) light. This invisible part of the spectrum causes some substances to fluoresce and glow under UV light. We demonstrate this effect best in low light levels using Ultraviolet light, similar to those used in the beauty industry or to inspect bank notes. 

Fluorescent lamps.


A fluorescent tube, also known as a fluorescent lamp, is a type of gas-discharge lamp that uses low-pressure mercury vapour to create visible light through fluorescence. When an electric current flows through the gas, it excites the mercury vapour, causing it to emit short-wave ultraviolet light. This ultraviolet light then causes a phosphor coating on the inside of the tube to glow and produce visible light.


Today, many people use black lights, A blacklight, sometimes called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave ultraviolet light and very little visible light.


The following image shows one of our small diamond parcels as it appears under ultraviolet light. Notice how fluorescence varies from nil to strong across the parcel. As one of our services, we screen small parcels of diamonds for clients who prefer no fluorescence. 

Why do diamonds fluoresce? Colours and intensities. 


The fluorescence is commonly blue and is caused by microscopic structures within the diamond.

Even though fluorescence is not usually considered in grading diamonds, it affects price. For example, If a colourless or nearly colourless diamond fluoresces under UV light, the price can decrease. One line of thought considers fluorescence as a characteristic with a negative impact on the appearance of the diamond.

However, some gemmologists disagree with this idea and believe that fluorescence does not always negatively affect diamonds. Some even think that fluorescence can enhance the colour of the diamond. As a result, there is a division of opinions regarding the impact of fluorescence on diamond pricing.

From our own experience, lower colour diamonds with blue fluorescence actually appear whiter. In such circumstances, some diamonds carry higher prices than expected due to the fluorescence. 

Several colours of fluorescence include blue, yellow, green, orange, and white. However, blue stands apart as the most common of these colours.

Approximately 50% of all diamonds exhibit some degree of fluorescence, seen under certain conditions, such as under a long-wave UV lamp. 

Around 10% of diamonds fluoresce strongly enough to make a noticeable difference to the diamond's colour when viewed in sunlight or low UV light.


When is fluorescence bad?


Some buyers worry about the negative impact on a diamond. From our own experience, some diamonds with strong fluorescence appear milky or hazy in bright sunlight. But remember, some diamonds appear milky, foggy or cloudy without any fluorescence present. For anyone worried about the appearance of a potential diamond, choose a diamond with no greater than medium fluorescence. 


Sometimes, jewellers create jewellery without realising some of the diamonds exhibit fluorescence. For example, in the case of three-stone diamond rings or diamond cluster rings. Checking each set of diamonds under UV lighting ensures consistency across a set of diamonds. In certain situations, one or more diamonds in a ring stand out under UV lighting, typically in nighttime venues such as nightclubs. 

When is a fluorescent diamond good?


Some buyers actively seek out diamonds with strong fluorescence owing to a significant cost reduction for many such stones. At the same time, fluorescence can be a positive trait. As already noted, blue fluorescence sometimes improves the whiteness of tinted diamonds. For example, J colour diamonds with a tinge of yellow. From above, such diamonds look far whiter than when they are viewed through the side of the stone


Diamond fluorescence scale GIA


To help classify the degree of fluorescence, the Gemological Institute of America (GIA) developed a five-level system. 

The levels include none (meaning no fluorescence), faint, medium, strong, and very strong. 


Faint vs none fluorescence


In our experience, little difference exists between two diamonds with faint or nil fluorescence. The difference rarely affects price and certainly does not affect the appearance of a diamond. For this reason, we rarely differentiate between each grade unless clients specify one or the other as a requirement. 

Further information from GIA


For more information and an in-depth discussion, we have added the following GIA video to view. 

Lab-grown diamond fluorescence


Lab-grown diamonds provide an alternative to naturally mined diamonds. Since they feature the same physical and chemical properties as a natural diamond, fluorescence occurs in man-made diamonds. Traces of Boron and Nitrogen create fluorescence in certain conditions, resulting in the same glow when placed under ultraviolet light.