Coloured diamonds attract a lot of attention nowadays – the post I have written a week ago based on a photo with coloured rough diamonds in a (Bahia?) Brazilian parcel attained record views on this blog and comments on Linkedin and Facebook.

For those professional gemologists addicted (or just mildly interested) in pink – red diamonds I have just come across an interesting article on the subject (just publicised by Tracey Greenstein in Linkedin).

Chromism-in-pink-diamonds, by John Chapman of Rio Tinto Diamonds and published in The Australian Gemmologist (Fourth Quarter 2014, Vol 25 – Number 8). The article is well written and discusses temporary color fluctuations either result of the polishing process, high temperature or illumination by short wavelength light of high intensity.These fluctuations are relatively short-lived. The author summarises his findings in the article’s first section:

Pink diamonds from Argyle have been known by polishers, laboratories and traders to exhibit a phenomenon of photochromism whereby their colour can be influenced by illumination of different lights and intensities. The influences are relatively short-lived and most conspicuous after illumination by short wavelength light of high intensity. This effect is particularly noticeable when using instruments to observe fluorescence, such as DiamondView, which after use with Argyle pink diamonds results in a distinctively bleached or pale colouration. Intensification of the colour can be achieved by subjecting pink diamonds to elevated temperature – thermo-chromism, while the colour can also change unpredictably during polishing – a phenomenon known as tribo-chromism. All these possible changes are temporary and the colour can be readily returned to an ‘ambient resting colour’.

Reference to pink diamonds in this article applies primarily to Argyle pink diamonds (Figure 1) rather than Golconda-style Type II pinks or type I purplish colours from Siberia or Canada.

Better read the full article (pdf in link above or at The Fancy Colour Research Foundation website) .