Diamond treatments

In 16th century, a sculptor and goldsmith from Florentine, Benvenuto Cellini wrote some of the first descriptions about gem treatments. The treatments on diamonds are done to enhance the colour or to hide some of the imperfections.

 

Irradiation is exposure of a material to radiation, which causes colour change in diamond.

All green diamonds get their colour from exposure to radiation, whether natural or lab-created. This 3.06-ct diamond colour treatment was disclosed, but the laboratory process is so similar to natural irradiation that it would be otherwise impossible to prove the origin of its colour.

 

 

Annealing is a controlled heating and cooling process, which is another way to change diamond colour. When it follows irradiation in a two-step process, annealing modifies irradiated colours to produce brown, orange or yellow. Rarely, it can also produce shades of pink, red or purple.

This 0.55-ct synthetic diamond was originally brownish but a combination of irradiation and heating turned it in attractive red.

 

 

 

 

 

A combination of high pressure and high temperature also changes diamond colour as a result in two different processes. One process improves the colour of brownish Type IIa diamonds, making them almost colourless. The other creates green or yellowish green diamonds from brown Type I1.

          
Before processing, these Type IIa diamonds ranged from grades N to Fancy Light (top). After processing, they received colour grades from D to H (bottom).

 

 

Laser drilling allows drilling tiny tunnels – thinner than a human hair – into diamonds to reach dark inclusions. This process uses a carbon dioxide laser to heat a tiny area of the diamond until it evaporates, producing a tiny tube that the operator can direct toward an unsightly inclusion. In spite of the fact that it disguises an existing inclusion, laser drilling often does not improve the clarity grade.

          
Before laser drilling, dark included crystals stand out in high relief against the rest of the diamond (left). After the diamond is laser drilled and the crystals are bleached with acid, they are much more obvious (right).

 

 

Fracture filling is a treatment that involves injection of molten glass substance into a diamond's surface-reaching feathers or laser drill-holes, thus improving the diamond's actual clarity.

          
The white feathers in this 1.39ct Fancy Intense pink emerald-cut diamond (left) detracted from the stone's colour. After the diamond was fracture filled (right), most of the feathers became transparent, and the stone revealed a more highly saturated pink colour.