gems, corundum, inclusions.5

The behavior of certain fluid inclusions in natural corundum during high-temperature heat treatment processes has been examined before and is relatively well known (Koivula, 1986). From such studies and observations, the condition of fluid inclusions has become an extremely useful means of determining whether or not a particular ruby or sapphire was heat-treated to alter its color and/or clarity. But when it comes to the behavior of solid mineral inclusions during the heat treatment of corundum, much less is actually understood. This leads to speculation and “best guessing” in the diagnosis of heat treatment in instances where solid inclusions are the determinant characteristics.