Diamonds Used for HPHT Treatment

Abstract

Type, color and clarity are three major parameters, which determine suitability of diamond for HPHT treatment. Clarity is the major limiting parameter. Low clarity diamonds with many inclusions may considerably stimulate internal graphitization and development of cracks during HPHT annealing making HPHT treatment useless. Diamond type is a technological rather than commercial parameter of diamond. It is a key factor for determination the HPHT treatment conditions, which could allow to achieve desirable final color. In this chapter, natural occurrence of diamond types and the methods of their recognition are discussed. Diamond color is of primary commercial importance. Initial color serves as the reference point for the evaluation of the improvement of diamond’s appearance and the increase in its price after HPHT treatment, as well as the effectiveness of the HPHT treatment procedure. Typical colors of natural diamonds used for HPHT treatment are discussed. A particular attention is paid to natural diamonds of brown color, which are the most common starting material for commercial HPHT treatment.