corundum, synthetic corundum.7, gems

Gübelin discusses the identification of newly available synthetic and treated blue sapphires, concentrating on Chatham flux-grown synthetic sapphire and on natural sapphires whose color has been modified by heat treatment or surface diffusion. He describes the crystal habits and physical and optical properties of rough and faceted Chatham material, followed by a detailed examination of diagnostic inclusions, some of which closely resemble inclusions in natural sapphire. Twenty-three color photomicrographs illustrate these features. A further 15 photomicrographs document characteristics of color-enhanced sapphires, including altered mineral inclusions surrounded by tension cracks, pockmarked girdle surfaces, pronounced color zoning, and concentrations of color in surface-reaching fractures.