Heated rubies
Most rubies 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 rubies
Fractures and surface cavities in rubies 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 rubies
Diffusion treatment involves exposing the surface of a ruby to certain chemicals and then heating it over a prolonged period of time until the ruby absorbs the chemical and changes color.

Usually only very pale, poor color rubies are used. Note that the color is confined only to the surface of the sapphire. This could be a problem if the ruby is ever chipped and needs to be recut or repolished. Diffusion is also used to produce star rubies. This form of treatment is still considered controversial.