Grey diamonds, closely related to Blue diamonds, have throughout the past decades become increasingly popular. At their best, they feature a striking pure grey to bluish grey hue. Variations of grey commonly observed and mainly differing in saturation also include silver-grey to mouse-grey, pencil-grey or steel-grey.
The colour grey is either caused by numerous minute graphite platelets locked inside a diamond’s crystal or as is the case with most fine quality greys by the presence of structural defects related to hydrogen impurities. Argyle Type Ia greys with their signature absorption line at 550nm are a good example of this. Old Indian Golconda Greys, on the other hand, are beautiful examples of Type IIB diamonds in which hydrogen along with tiny amounts of boron has been subjected to plastic deformation. They’re resultant, rich very slightly bluish grey colour is caused by markedly less absorption in the near infrared visible light range when compared to typical blue Type IIb diamonds. These stones also feature notable weak yellow, yellow-green to orange or even red phosphorescence.
All the aforementioned causes lead to selective absorption of visible light broadly across the entire light spectrum. The returning wavelengths then recombine to appear as grey to the observer.
Grey in diamonds may be modified by various colours including green, olive, yellow or brown, but only those possessing a secondary pink or better purple, blue (caused by boron) or violet (also hydrogen) hue are considered pretty. All other less attractive colour combinations usually appear dull and spark little commercial interest.