What is diamond fluorescence? Is it good or bad? Does it affect diamond colour and its price? Let’s go into details and find answers for some of the top questions raised when shopping for diamonds.
What is Diamond Fluorescence?
Diamond fluorescence is the ability of the stone to emit visible light and change its colour when subjected to ultraviolet (UV) rays from sources like the sun and fluorescent lamps. Once the UV light source is removed, the diamond stops fluorescing.
Natural diamonds exhibit the strongest fluorescence under long-wave UV rays, while synthetic diamonds show the reverse reaction – they exhibit the strongest fluorescence under shortwave. Although natural diamonds can fluoresce almost any colour, the most common colour seen is blue, on rare occasions they glow yellow, orange, green, white and even red. Synthetic diamonds exhibit green, yellow-green, yellow, orange and vivid red.
It is worth mentioning that not all diamonds fluoresce. Only around one-third of all diamonds exhibit some degree of fluorescence.
The cause of fluorescence is hidden within the stones. Diamonds contain different chemical elements, such as aluminium, boron and nitrogen, which react in the dark depending on their concentration and cause diamonds to glow.
Diamond Fluorescence Grades
Diamond fluorescence is an identifying characteristic which is described by its intensity. Depending on the level a diamond can glow, the Gemological Institute of America (GIA) describes a diamond’s fluorescence on the following scale:
- None – no fluorescence present, no effect on colour
- Faint – weak fluorescence with minor effect on colour
- Medium – moderate fluorescence with a small effect on colour
- Strong – strong fluorescence with a drastic effect on colour
- Very Strong – very strong fluorescence with a drastic effect on colour
To evaluate the fluorescence grade, grading laboratories use UV spectrum lights and a set of fluorescent diamonds for comparison. Every loose diamond (including fancy colour stones) with a GIA grading report, has a fluorescence grade assigned. The information on this can be found in the “Additional Grading Information” section.
Does Fluorescence Affect Diamond Colour?
While fluorescence does not affect a diamond’s colour grade, its strength can alter the appearance of a diamond colour when viewed under certain lighting conditions.
Depending on a diamond, fluorescence can either improve the diamond’s colour or make it appear oily and hazy.
In some cases, blue fluorescence can mask and improve yellow tint of lower colour grade stones, especially in diamonds with I to M grades. Blue fluorescence tends to make faint yellow diamonds appear more colourless in natural daylight or other types of UV light. As a result, near colourless to faint yellow diamonds with Medium to Very Strong blue fluorescence may have a slightly higher per-carat price than similar diamonds with no fluorescence.
Diamonds with higher colour grades (D to H colour range) with blue fluorescence are often considered less desirable. Some believe that blue may cause oily appearance in these diamonds if fluorescence intensity is Very Strong. In fact, not all diamonds with Very Strong fluorescence grade look oily, however, they all cost less than diamonds that do not have fluorescence.
As a general rule, strongly fluorescent diamonds are considered to be negatively affected which is why such diamonds usually have lower prices compared to similar non-fluorescent stones.
Is Diamond Fluorescence Good or Bad?
Fluorescence is neither good nor bad. However, the effect of fluorescence on a diamond’s colour is a controversial topic.
GIA has conducted a study on blue fluorescence and concluded that it does not affect the quality of the stone for an average observer. However, some jewellers claim that in their experience, diamonds that exhibit strong fluorescence tend to appear foggier. Others say that it does not have a significant effect on the appearance of diamonds. That is why you need to decide for yourself if a particular diamond looks good to you.
When shopping for diamonds, ask the jeweller to show the stone under both UV and normal lighting. Do not forget to look at the stone when it is exposed to daylight as well. Sunlight contains UV rays, which will bring out your stone’s fluorescent colour.
If a stone is fluorescent, compare it with a non-fluorescent diamond of similar quality and check if you can see any difference in colour as the most important is to love what you end up with.