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Meet the Experts HPHT treatment


High Pressure High Temperature Treatment

high pressure treatmentContinuous developments in technology have created different treatment techniques used to improve the appearance of diamonds. The colour of particular types of diamond can be altered artificially by subjecting them to conditions of extreme heat and pressure. The colour of a diamond following HPHT- treatment is dependent on the exact conditions used and the diamond type. The HPHT process is perfectly acceptable so long as it is disclosed to the purchaser.

Scientists divide diamonds into various types. The vast majority (over 97%) of diamonds handled by the jewellery industry are called Type I. A tiny minority of diamonds (approx. 2%) are called Type II.

These two types can then be further classified into Type Ia and Ib, and Type IIa and IIb.

HPHT deals with Type IIa diamonds which have no nitrogen and are colourless. These Type IIa diamonds due to crystal lattice defects sometime show brown colour. Putting the diamond under high pressure and high temperature results in a repaired crystal lattice, and a colourless diamond.

In Type Ia diamonds the HPHT process causes dispersion of paired nitrogen into single nitrogen molecules and cause the diamond to take on a colour of fancy yellow to yellow-green. This transforms a unsaleable poor coloured diamond into a valuable fancy coloured diamond.

HPHT- treated diamonds are impossible for gemmologists to identify using standard gem testing instruments and therefore, undisclosed HPHT- treated diamonds are a great concern to the gem and jewellery industry. However, AnchorCert has invested in the latestest technology which can help identifiy HPHT-treated diamonds. All diamonds submitted to AnchorCert are screened and examined to ensure they are natural. If a diamond shows signs of having been exposed to treatment, further tests would be carried out to identify if the stone had been subject to HPHT treatment. AnchorCert are the only UK diamond grading authority equipped to identify this.


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