Many people are familiar with Marilyn Monroe’s performance of ‘Diamonds Are A Girl’s Best Friend’ in the 1953 film ‘Gentlemen Prefer Blondes’. Dripping in ice white diamonds and surrounded by well dressed men offering her yet more, one could be forgiven for thinking that all diamonds are indeed ‘colourless’. Whilst the majority of gem quality diamonds used in jewellery are indeed ‘colourless’ a tiny proportion of these stones exhibit distinct colouration.
So how rare are naturally coloured diamonds? Out of 10,000 carats mined only 1 carat will be gem quality fancy coloured or to put it another way, of the 110 million carats of diamonds produced annually (80% being used in industry) only 2000 carats will be cut and polished coloured diamonds. To put this into perspective consider this: the huge Argyle Diamond Mine in the Kimberley region of northern Western Australia is famed for it’s production of pink diamonds yet of the 30 million carats produced annually only 590 carats are of gem quality; of this less than a 1/10th of 1% are pink diamonds.
So why are some diamonds coloured? Whilst the vast majority of diamonds fall in to the D-Z GIA colour ranges (most ‘white’ diamonds fall in to the D-H range http://gia4cs.gia.edu/en-us/diamond-color.htm) nature also produces diamonds that are yellow, pink, blue, brown or green in colour. These colours are due to the very rare geological conditions in which the diamonds have grown as well as impurities in the chemical make up of the stone. Now here comes the science so let’s try to keep this as simple as possible:
“Diamonds are separated into two different types; namely Type I and Type IIa. Type I diamonds contain nitrogen while Type IIa diamonds are nitrogen free and are usually white, brown or pink and very rarely red or green. Type IIa and Type IIb (blue colour) are very rare and generally thought to comprise less than 1% of all diamonds. Because of the absence of nitrogen, Type IIa diamonds can never be yellow” (source http://www.gemdiamonds.com/gem/en/about/diamonds/what-is-a-gem-diamond/)
Coloured diamonds vary tremendously in their in hue, tone and saturation – the deeper the hue, the richer the tone and the intensity of the colour saturation all contribute to making a diamond more or less desirable. The GIA has set grading classification standards that are accepted worldwide: coloured diamonds are assessed for hue against 27 different shades and tone and saturation are determined in strict lighting and viewing conditions.
The coloured stones in the ring pictured above are all diamonds. The ring dates from C1900 and is set with three old cut stones: a blue diamond (1.02cts), a pink diamond (1.45cts) and a yellow diamond (1.28cts) with small white diamonds set to each shoulder. The ring was brought to us for an assessment of the settings by the owner who was anxious about the safety of the diamonds. The settings were photographed using our microscope camera (hence the poor quality!):
The ring had been worn daily for the past 25 years or so and not surprisingly was showing the effects. Two claws were missing from the centre pink diamond and all the claws were worn, especially those to each end; the sides of the ring were worn flat and the shank was also thin. In addition a small diamond was missing from one shoulder. The thought of losing one of these diamonds was too horrendous to contemplate, so difficult would it be to find a suitable replacement.
All the diamonds were removed and the claws were replaced; the side settings were built up and a replacement old cut diamond was supplied and set to one shoulder. The thin shank had resulted in this otherwise top-heavy ring spinning around on our customer’s finger so two small gold beads were fitted to the inside of the replacement shank to give the ring some stability and to reduce it’s tendency to spin round when worn. The results can be seen at the top of the page and in the gallery below:
These images show perfectly the distinct colouration to these diamonds. The pictures were taken in a light box and, short of cropping, have not been edited in any way so the colours are a faithful representation of those seen when these stones are viewed in daylight. They look gorgeous and our customer was thrilled to be re-united with her ring once the restoration was complete. These diamonds have been faithful ‘friends’ to our customer for over 40 years and now the settings are safe can remain so for many more years to come.
Damon Barker FGA