EGL USA has announced the discovery of the first visual observational criteria for identifying high-pressure, high-temperature treated (HPHT) diamonds.

The indicator, called the "fluorescence cage," is a specific luminous, intersecting pattern along the cut edges and vertices of facets on particular colored HPHT-treated diamonds with less than strong fluorescence.

The effect is observable with a fluorescence microscope. According to early results, the effect is the result of the movement of optically active impurities triggered by the HPHT process.

Dr. Inga Dobrinets of EGL USA and Professor Alexander Zaitsev of the College of Staten Island/CUNY, conducted research to identify the cage.

Dobrinets stated: "The visual observation of a fluorescence cage appears to be the most reliable feature used so far for the reporting of HPHT treatment. A significant advantage of the cage-based identification is its comprehensive fidelity and technical simplicity. While the 'cage effect' may not appear on all HPHT-treated diamonds when it is evident, a conclusive identification can be made on that basis alone."

EGL USA stated that it plans to utilize the technological breakthrough to provide HPHT identification more efficiently and cost-effectively. The lab noted that it will continue to study the cage effect and set out final findings for inclusion in a formal paper.