The mechanism of flux healing of a fracture in corundum. A. Open fracture/fissure, unhealed. B. During heat treatment, flux enters the fracture and dissolves the walls of the crack. C. During cooling, dissolved corundum recrystallizes in the crack, thus healing it closed. The newly crystallized ruby is essentially a synthetic ruby grown in the crack alone. It contains small pockets of now-solidified flux glass, along with some trapped gas pockets. For purposes of this diagram, the surrounding natural ruby and the synthetic ruby in the crack are shown in two different colors. In reality, no distinction can be seen between the surrounding ruby and the newly grown synthetic ruby. D. Any flux glass present on the surface can be dissolved away with acid. The synthetic ruby in the crack is unaffected by the acid, as is the ruby as a whole. (Illustration: R.W. Hughes; modified from Hänni, 2001, SSEF). Lotus Gemology.
{}