Color zoning, which forms from growth layers that build up during the formation of the stone, is present in certain sapphires. However, uniformity of color is an important factor in a sapphire's value. Colorless and pale blue sapphires from certain localities may be heat-treated to give them an intense blue color. Heat-treatment may also improve the clarity of some sapphires by removing tiny inner inclusions . Sapphire is pleochroic , displaying a lighter and more intense color when viewed at different angles.
Some pleochroic sapphire is blue when viewed at one angle, and purple at a different angle.
A rare variety of sapphire, known as color changing sapphire , exhibits different colors in different light. In natural light, color changing sapphire is blue, but in artificial light, it is violet. This effect is the same phenomenon seen in alexandrite . Sapphire was first synthesized in 1902. The process of creating synthetic sapphire is known as the Verneuil process .