How to judge Black Diamond

BLACK diamond is a variety of diamond that was once held in low esteem. Today, however, it has found favour amongst some of the world’s innovative jewellers. The credit goes to Swiss jeweller Fawaz Gruosi, who started the trend with his one-of-a-kind black diamond jewellery collection and watches. Since then, black diamond has been catapulted into the world of fine jewellery, and is no longer just a by-product of mining.

Colour: The colour of black diamond ranges from grey to black. Darker, even shades are more desirable.The presence of numerous inclusions, sometimes lining cleavages and fractures, results in the black colour. Natural black diamonds are heavily included, while pure black, a rarer type, may look similar to black onyx. To judge colour, use a transmitted, reflected and fibre-optic light source to observe the colour contrast. The best natural black diamonds are not easy to find.

Cut: Black diamonds are cut brilliant and in other popular shapes, depending on the size and shape of the rough. They are very hard to polish and require great care in setting. They are widely used in pave settings. In order to simulate an antique look, black diamonds are also cut briolette for necklaces and earrings.

Clarity: Pits, cavities and polishing lines, visible under magnification, are due to cleavages, fractures and other inclusions (graphite). The variable presence of magnetite, hematite and native iron may cause unusual magnetic properties.Such properties may be useful for differentiating natural black diamond from artificially coloured ones.

Treatments: Black diamonds can be treated by irradiation to enhance their colour. Artificially irradiated stones may show a very dark green colour under fibre-optic or a transmitted light source.Unfortunately treated black diamonds are also used in antique jewellery reproductions, and as replacement stones in old settings. All treatments should be disclosed.

Synthetic and Simulants: Synthetic black diamond is opaque. Proper magnification and fibre-optic lighting may reveal metallic flux inclusions.The most frequently encountered simulants are synthetic black (non-transparent) cubic zirconia, black onyx, hematite and imitation hematite. Most simulants can be distinguished based on gemological properties.