When a rutile-silk containing sapphire (such as this stone from Kanchanaburi, Thailand) is heated, the titanium from the rutile moves into solid solution in the sapphire, coloring the area around the rutile blue, creating a distinctive “ink spot” internal diffusion pattern.
Natural Sapphire • Thailand (Siam); Bo Ploi • Enhancements: Heat (H) • Lighting Conditions: Diffuse Light Field (Transmitted Light)
Photographer: E. Billie Hughes •
Image Number: A-001-0859-1 • Date Posted: 21 April 2015
Koivula, J.I. (1987) Internal diffusion. Journal of Gemmology, Vol. 20, No. 7/8, pp. 474–477; RWHL*.