corundum, treatments.6, gems

The article gives a brief history of corundum heat treatment, from ancient times until the appearance of heat-treated Sri Lankan geuda sapphires in the late 1970s. While there are specific reports mentioning corundum heat treatment dating back almost 1000 years, these involved low temperatures. High-temperature heat treatment of corundum is largely a product of the 20th century, and was probably discovered during experiments on the reconstructed ruby known as the ‘Geneva ruby’. Heat treatment of Anakie sapphire to improve clarity was reported as early as 1916.