50% of all diamonds have fluorescence emitting a light blue or sometimes light green colour in certain lights. This can only be seen in most cases under longwave ultra-violet light.
When diamond dealers started to try to secure a common set of colours so the diamonds could be explained to each other and traded more freely. The top diamond was called a Jager. This was the finest blue white diamond and the name comes from the mine in South Africa called the Jagerfontein mine.
They then realised that the light blue was fluorescence, as they appeared as different hues in different lights. The blue hue appeared as the result of concentrated ultra-violet rays of light in natural light. On realising this they changed the order of quality and the River diamond which had been the 2nd quality became the top stone. This was after diamonds found in rivers and alluvial deposits, as these stones were normally very clean and very transparent. The reason for this is the stones have been eroded out of the pipes they were formed in over millions of years and have been washed down stream. The lower grade diamonds have been eroded away over the years leaving only the best hardest purest stones intact.
This has now been changed to the grading system we have in place today. Ranging from D downwards. ABC has not as yet been used to grade the colour of the diamond in case a better-coloured diamond appears in the future.
Discussing this always reminds me when I was finding a diamond for Jonathon a client and hopefully more than this. He wanted a large marquise for his wife as a special present. So 2 days later I had found 2 stones that were very nice and great value for the money. The dealers I normally deal with did not have what we were looking for. I had found a couple of very good stones from an Antwerp dealer I have a lot of dealings with Ari a chap I have dealt with on a few occasions in Antwerp his family have been in diamonds for generations and have there own cutting firm.
I talked to Jonathon at lunchtime, after 2 days looking at diamonds your eyes become very sore. He then asked me to save one of the stones, which I went back to do after seeing the dealer with the stone.
I happened by accident to come across a D coloured stone with stunning proportions and no fluorescence. Just within the price range. The other stones were larger and most people would have chosen the larger heavier stone. Most of the time I would have recommended the larger stones but this stone was the best without a doubt there was no comparison. It was the best marquise in this particular large size I have ever seen. So an hour later and a bit more haggling the stone was purchased.
The American dealer was also one of the few dealers who really had the same passion for the stones as I do which showed in his stock.
Most of the time the fluorescence in diamonds cannot be seen in most lights. Some types of fluorescence can effect the stone very badly in certain lights. Also the fluorescence tells you how to mount the stone in some cases. I have seen stones that look stunning in white and natural light. Then when you walk into a room where one of the lights is slightly yellow (a dirty fluorescence tubes is the worse) the stone with certain florescence will take on a petrol colour and lose a lot of fire.
A badly fluorescence stone would not be set in a rub over setting as the stone would loose a lot of its fire and colour. I have seen a very expensive pink diamond set this way and then the seller wondered what had happened. I did not like to point out the problem at this point as he did not know about the fluorescence properties. I don't think his boss who was not hands on would have been too pleased.