Fluorescence in Diamonds

Diamond Fluorescence: Historical Background

In Europe, before the age of diamond certification, the most highly regarded diamond colour was ‘blue white’. This term describes near-colourless to light yellow diamonds with a strong blue fluorescence, stones that were actively sought by merchants thanks to their appealing ‘ice’ effect.

It was later observed that strong blue fluorescence was a quality sometimes found in hazy stones, a fact that led dealers in the 1970s to offer what they termed ‘milky Ds’ (diamonds with a colour grade of D, very strong blue fluorescence, low transparency) at significantly reduced prices. This had a knock-on effect during the years that followed: eventually even F grade diamonds and those with a weaker fluorescence were being marked down in price.

top

Why Do Diamonds Fluoresce?

Diamond is crystallized carbon. This process occurs about 75-125 miles below the surface of the earth, usually where volcanic or ancient volcanic sites exist. A diamond will become fluorescent if there are traces of the mineral boron present in the earth during the crystallization process. The boron particles become excited when exposed to the particular wavelength of UV light and give off a fluorescent light as they revert towards their relaxed state.

Diamonds can fluoresce in a variety of colours – blue, yellow, green, orange and white – but blue is the most common. It is estimated that around 50% of diamonds have fluorescence that can be seen in special conditions e.g. under a short wave UV lamp, while around 10% fluoresce strongly enough to make a noticeable difference to the colour of the diamond when viewed in sunlight or incandescent (low UV) light.

There are five levels of diamond fluorescence described by the GIA: None (i.e. no fluorescence), faint, medium, strong, very strong. According to the GIA Gem Trade Laboratory, strength of fluorescence does not directly correlate to either colour or clarity. In other words, it is possible for two diamonds with completely different clarity and colour grades to exhibit exactly the same strength of fluorescence.

Figure B.

Figure C.

Figure A shows the relationship between absorption and luminescence (the emission of light by a substance that has absorbed UV radiation.) The figure shows an electron moving from the ground state to an excited state (north arrow) when UV radiation is absorbed at a luminescence center. When the electron moves to a slightly lower state it loses some of its energy (wavy arrow) and no light is emitted. Subsequently, it returns to the groundstate (straight down arrow), releasing energy, or light, as fluorescence.

Figure B & Figure C show the varying levels of fluorescence on diamonds viewed table-down and table-up. The levels are as follows: 1. Very strong, 2. Strong, 3. Medium, 4. Faint, 5. None.

top

How Does Diamond Fluorescence Impact Diamond Pricing?

Historically, strongly fluorescent diamonds have been marked down in price next to their non-fluorescent counterparts. The Rapaport Diamond Report, the industry’s weekly price guide, provides a good indication of the influence of fluorescence on market value. In their November 7, 1997 report, for example, some higher colour (D-H) non-fluorescent diamonds were listed for up to 15% more than similar stones that exhibited very strong blue fluorescence.

In the same report, however, lower colour (I–N) diamonds with very strong fluorescence were priced up to 4% higher than similar non-fluorescing stones. This is likely due to the perception that blue fluorescence can mask the undesirable yellow tones found in some stones. Learn more about diamond colour.

top

The GIA Study on Diamond Fluorescence

Despite a long history of debate on the issue of fluorescence and pricing, there had been no studies that examined the influence of blue fluorescence on the appearance of a diamond under normal viewing conditions until the GIA undertook their 1997 experiment.
Colour assessment in grading laboratories takes place under carefully controlled lighting and viewing conditions and mainly with the diamond positioned table-down. However, in a jewellery store or showroom a diamond will normally be examined table-up and in a variety of lighting conditions, as it almost certainly would be when the item is worn. With this in mind, the GIA set up their experiment to study the influence of fluorescence in a range of lighting conditions and by observers from both within and outside the diamond industry.

In the experiment, a range of diamonds with very similar proportions, clarity and symmetry, but differing ranges of blue fluorescence, were assembled. Diamonds of similar colour grades were grouped into sets to represent important commercial breakpoints. These sets were then examined in a wide variety of viewing environments, from the controlled conditions found in laboratories to rooms with only natural sunlight. A total of 46 observers were assembled to represent both the diamond industry and the diamond-buying public.

For the non-industry observers, considered to represent the diamond consumer, fluorescence had no effect on colour and appearance. For the experienced industry observers, the GIA found that the strength of fluorescence had no widely perceptible effect on the colour appearance of diamonds when viewed table-down. What’s more, when the diamonds were viewed table-up, as they would be in a jewellery store or showroom, the experienced observers actually reported strongly and very fluorescent diamonds as having a better colour appearance than the less fluorescent stones.

The GIA discovered that while the effect of fluorescence on colour was most noticeable in stones within lower colour grades (I and K), in the marketplace the influence on price is greater in stones with higher diamond colour grades (D through H). This challenges the trade perception that fluorescence usually has a negative effect on better-colour diamonds. They also found that, contrary to popular belief, fluorescent diamonds aren’t as common as non-fluorescent diamonds.

The GIA report concluded that “the diamond industry would be better served by considering each individual diamond on its own visual merits.”

top

Should I Buy a Fluorescent Diamond?

It’s important for you to be happy with the diamond you purchase. As shown, fluorescence can greatly enhance the colour and appearance of a diamond and shouldn’t be looked upon unfavourably; only in exceptionally rare cases will fluorescence cause the diamond to look milky, oily or hazy.

This is what our Seventy Seven Diamonds diamond expert Vadim Weinig advises: “Whilst the commercial image of fluorescent diamonds has taken a blow since the 70s, my personal opinion is that fluorescent diamonds are currently under-valued, and can, most of the time, bring more positives than negatives to a diamond. Of course, one needs to be aware that the more fluorescence there is in a diamond, the bigger the chance the diamond will be milky, nevertheless, even for strong fluorescent diamonds, that chance is still remote”. It always comes down to a subjective decision, but best practice would be to consult a diamond specialist before purchasing to ensure you make the right choice.

top