corundum, ruby, treatments.6, inclusions, gems

Gunawardene discusses the identification of heat-treated and diffusion-treated ruby, with particular attention to treatment practices observed in Thailand and Sri Lanka. High-temperature heating can modify ruby colour and clarity, while diffusion treatment introduces colouring agents into a shallow surface layer. The paper describes conventional gemmological and microscopic features useful for recognizing treatment, while emphasizing that heat treatment alone may in some cases leave insufficient evidence for unequivocal identification. Diffusion treatment is generally more readily detected from the distribution of colour, particularly concentrations associated with the stone’s surface and facet geometry. The author also describes practical aspects of the treatment processes and discusses the problems such treatments pose for identification and the gem trade.