What is Fluorescence?

What is fluorescence?
Certain diamonds emit a subtle blue glow when exposed to ultraviolet rays. This interesting phenomenon is called fluorescence. Many light sources including the sun, fluorescent office lights, and "black" lights emit ultraviolet rays. In normal lighting conditions, fluorescence cannot be seen.

Different strengths of fluorescence can be exhibited in diamonds, brought about by the presence of sub-microscopic particles. It is one of the identifying characteristics of a particular diamond and can be seen sometimes in daylight and under some artificial lights due to the presence of UV radiation. The most common form found is blue fluorescence. The presence of fluorescence does often affect the price of a diamond, with strong fluorescence resulting in a slightly lower price. Occasionally strong blue fluorescence can result in a slight milky appearance to the diamond as mentioned above. It is therefore necessary to view such diamonds "in the flesh" as often, this slight milkiness cannot be observed.

The presence of fluorescence can actually be advantageous in certain diamonds. Lower coloured diamonds that are very slightly tinted in colour when viewed from the side, can appear much whiter when viewed table-top up, due to the presence of blue fluorescence. This itself can result in a slightly higher price on such lower colour diamonds due to this "improving" characteristic.

Observed in everyday life, fluorescence will probably not be observed by the wearer unless under certain conditions. At a nightclub for example, any one of a set of diamonds may be seen to "glow" when viewed under the UV lights. This is at no detriment to your jewellery and under normal conditions this not noticed.

In simple terms, fluorescence is the tendency for a diamond to absorb radiation from an ultra violet light and emit it as visible light. The most common colour of fluorescence is blue.

Grading Fluorescence

A diamond's fluorescence can be given a grade from "none" to "very strong", with faint, medium and strong in between.

Fluorescence can either be graded manually, or with the aid of machines

Most Diamond laboratories indicate the strength of fluorescence on their diamond certificates for identification purposes. The appearance of fluorescence in diamonds exposed to strong ultraviolet lamps ranges from very faint (barely perceptible) to very strong (a neon-blue glow). Some diamonds show no fluorescence at all.

In a minute number of cases, diamonds with very strong fluorescence and a special arrangement of clarity characteristics may look slightly "cloudy," but consumers rarely encounter such diamonds. Fluorescence may also have a slightly positive influence on the appearance of certain off-coloured diamonds, thereby making them more desirable to own.

Colour vs. Fluorescence

Blue fluorescence has the ability to "cancel out" or reduce the tint of more yellow (lower colour grade) diamonds. A GIA survey even found that more fluorescent, especially more yellow and therefore lower graded diamonds were favoured over their non-fluorescent counterparts.

Effect on Pricing

It is generally accepted that the greater a diamond's fluorescence, the less it will sell for. However in the UK, fluoescence is barely mentioned and often discounted from a price perspective.

Cloudiness or Oiliness Caused By Fluorescence

A very small number of stones with strong or very strong fluorescence appear "oily" or "cloudy". Whilst this is quite rare, it is always advisable to look at a stone with strong or very strong fluorescence before purchasing.

Other Colours of Fluorescence and Phosphorescence

Whilst very rare, diamonds can emit yellow or orange fluorescence, whilst some diamonds may even continue to glow after the UV light source has been removed. These diamonds display phosphorescence.

Buying Tip:

When looking at diamonds, ask your jeweller if you can observe the stone in a dark corner under UV light, remember that the phenomenon is totally harmless and can be great fun in a Night Club environment where your stone will glow with a magical brilliance. Dont reject the stone, enjoy it.

All NAG Registered Valuers and members of theAassociation of Independent jewellery Valuers (AIJV) will be able to advise if your stone is fluorescent or not