Just like ruby, sapphires are subjected to a wide variety of heat and fracture-filling treatments. And, just like ruby, any heat, fracture-filling or other type of treatment should be disclosed to buyers.

Spectacular Heat Treatment Results:

Some rough materials that have no trace of blue color can be heated to produce a spectacular blue. Some milky to yellowish, cloudy to translucent corundum can be heated to yield stones that are transparent and bright blue. If such treatments have been used, sellers should disclose the types of treatments to potential buyers when the stone is presented for sale.

Lattice Diffusion

Some sapphires are treated by a process known as “lattice diffusion.” In lattice diffusion, the sapphire is heated in the presence of a material that will release tiny metal ions. When the corundum is heated, its lattice expands enough that these tiny ions can diffuse into the gem and become trapped within the lattice when the corundum is allowed to cool. The trapped ions prevent the corundum from contracting to its normal dimensions, producing a defect that alters the color of light passing through the gem.

Beryllium diffusion can produce orange, yellow and pink colors. Titanium diffusion can produce blue. Lattice diffusion treatment is considered to be a severe treatment that is sometimes hard to detect. Some people believe that corundum which has a color produced by lattice diffusion should not be called “sapphire.”