corundum, synthetic corundum.7, flux, Lechleitner, gems

Gunawardene examines an experimental product developed by Johann Lechleitner in which Verneuil synthetic corundum of various colours is used as a seed and overgrown with a thin layer of synthetic corundum. The study records the gemmological properties of these coated rubies and sapphires and concentrates on their identification. Magnification is particularly important: the Verneuil cores may show the curved growth structures and inclusions characteristic of flame-fusion corundum, while examination of the overgrowth reveals features associated with the coating process and the boundary between seed and overgrowth. The paper describes and illustrates these microscopic characteristics and discusses their usefulness in distinguishing the material from natural corundum and other synthetics. At the time of publication the process was still experimental rather than an established commercial production method.