Heat treatment enhancement of natural orange-red sapphires

Certain variety of Madagascar color sapphires (fancy sapphires) has orange-red color, which shades don’t let to consider them as the rubies. Heat treatment experiments in reducing atmosphere were carried out on such sapphires for the purpose of improving their color characteristics. Chromium (III), iron (II and III), titanium (IV) chromophore impurities in natural corundum and chromophore centers with their participitation are considered. A special attention is paid to spectral characteristics of chromophore centers. Behavior of the chromophore centers under heat treatment and their influence on the color of fancy sapphires are studied. Color modification mechanism was proposed on the basis of microprobe and spectral analyses data. The proposed enhancement technique allows to improve color characteristics of fancy sapphires.