Lattice diffusion is a treatment process which uses heat and chemicals to diffuse an element from an external source into a gemstone to change its color.  The mechanism by which atoms or ions move through solids is known as diffusion.  Even the most perfect crystal has places in its lattice where atoms are missing.  These holes are termed “vacancies.”  In the case of corundum, which is made up of aluminum and oxygen atoms, the higher the temperature, the more missing atoms there will be.  The color change depends on the type of element that is diffused into the corundum, its inherent chemical composition, and the conditions under which the diffusion processes takes place.

Early in 2002, a large number of pinkish-orange sapphires came into the jewelry market; it became apparent that corundum treated by a new technique had been introduced into the marketplace unannounced, particularly in Japan.  Careful research demonstrated that this new process involved diffusion of the light element beryllium (Be) into a wide variety of corundum types to alter their color.  It has been reported that at first chrysoberyl, which is a mineral made up of beryllium, aluminum and oxygen, was accidentally mixed in among the sapphires during the heat treatment process, and later purposely crushed chrysoberyl was added to the crucibles to release the necessary beryllium for the creation of the yellow color component. In addition to the change in color, these stones exhibit many other features—both internal and on the surface—that indicate very high-temperature heat treatment and/or long periods of treatment.

For more information on lattice diffusion, please see the following bibliography on our website:

Bibliography on Corundum Diffusion