When Sri Lankan yellow sapphires with exsolved particles are heat treated, magnesium exits the particles and creates yellow-producing trapped-hole color centers. The result is color concentration around the particles, a process termed “internal diffusion” by gemologist, John Koivula.

Natural Sapphire   •   Sri Lanka (Ceylon)   •   Enhancements: Heat (H)   •   Lighting Conditions: Diffuse Light Field (Transmitted Light)
Photographer: Richard W. Hughes   •   Image Number: A-001-1406-1   •  Date Posted: 19 June 2015

Koivula, J.I. (1987) Internal diffusion. Journal of Gemmology, Vol. 20, No. 7/8, pp. 474–477; RWHL*.

Rutile silk with vague blue zones in an untreated Mozambique ruby. Note that where the planes of rutile silk are concentrated, the blue color is absent. This is caused by what inclusion specialist John Koivula has dubbed “chromophore cannibalization.” Rutile consists of titanium dioxide and as it grows it sucks the titanium out of solid solution from the surrounding ruby, cannibalizing (removing) the blue color in the process.

Natural Ruby   •   Mozambique   •   Enhancements: None Detected (None)   •   Lighting Conditions: Diffuse Light Field (Transmitted Light)
Photographer: Richard W. Hughes   •   Image Number: A-001-0489-2   •  Date Posted: 21 February 2015

Pardieu, V., Sangsawong, S. et al. (2013) Rubies from the Montepuez area (Mozambique). Gemological Institute of America, October 5, 84 pp.; RWHL*.

Koivua, J.I. (2013) Useful visual clue indicating corundum heat treatment. Gems & Gemology, Vol. 49, No. 3, Fall, pp. 160–161; RWHL*.

Rutile silk with vague blue zones in an untreated Mozambique ruby. Note that where the planes of rutile silk are concentrated, the blue color is absent. This is caused by what inclusion specialist John Koivula has dubbed “chromophore cannibalization.” Rutile consists of titanium dioxide and as it grows it sucks the titanium out of solid solution from the surrounding ruby, cannibalizing (removing) the blue color in the process.

Natural Ruby   •   Mozambique   •   Enhancements: None Detected (None)   •   Lighting Conditions: Diffuse Light Field (Transmitted Light)
Photographer: Richard W. Hughes   •   Image Number: A-001-0485-2   •  Date Posted: 20 February 2015

Pardieu, V., Sangsawong, S. et al. (2013) Rubies from the Montepuez area (Mozambique). Gemological Institute of America, October 5, 84 pp.; RWHL*.