Brown diamond

There are several causes for the brown color, including irradiation treatment, nickel impurities and lattice defects associated with plastic deformation; the last is the predominant cause, especially in pure diamonds.

A high-pressure high-temperature treatment can heal lattice defects and convert brown diamonds into yellow or even colorless stones.

Diamonds occur in various colors, including blue, yellow, green, orange, various shades of pink and red, brown, gray and black.

Heating the irradiated diamonds to temperatures above 600 °C results in brown color associated with aggregation of the vacancies, with or without nitrogen involved.

[16] Such irradiation and annealing treatment can occur in nature because diamonds are often accompanied by uranium-containing ores which emit alpha particles.

Radiation treatment induces characteristic sharp optical absorption lines which can be easily detected by spectroscopic techniques.

Whereas the consensus has been reached that the color relates to the plastic deformation, the particular reason has been reliably identified (large clusters of vacancies) only in type IIa natural brown diamond.

In March 1999, Pegasus Overseas Ltd (POL) from Antwerp, Belgium, a subsidiary of Lazare Kaplan International, started marketing such diamonds that were processed by General Electric (GE).

The existence and identity of the treatment process was considered so important that micrometer-sized letters "GEPOL" were inscribed with a laser on the girdles of every treated diamond.