Heated sapphires
Most sapphires since the 1960s have been are routinely heat treated to improve their color and clarity. High application of heat dissolves some of the "silk" inclusions present in the sapphire. This form of treatment is considered stable and permanent. There is no real price difference between heated and non-heated sapphires.

Fracture-filled sapphires
Fractures and surface cavities in sapphires are also commonly filled with additives such as oil, wax, or epoxy resin to improve clarity or color. This form of treatment is considered stable and permanent.

Diffusion-treated sapphires
Diffusion treatment involves exposing the surface of a sapphire to certain chemicals and then heating it over a prolonged period of time until the sapphire absorbs the chemical and changes color. Usually only very pale, poor color blue sapphires are used. Note that the color is confined only to the surface of the sapphire. This could be a problem if the sapphire is ever chipped and needs to be recut or repolished. Diffusion is also used to produce star sapphires. This form of treatment is still considered controversial.