“Smoke Rings” in a Non-Beryllium-Diffused Sapphire
When analyzing corundum for evidence of heat treatment, one of the most useful and standard methods for gemologists is microscopic examination (N.D. Renfro et al., “Inclusions in natural, synthetic, and treated sapphire,” Summer 2017 G&G, pp. 213–214). Inclusion suites can start to alter at temperatures as low as 200°C. As the temperature rises, many inclusions start to show clear evidence of heat treatment, such as the internal diffusion of titanium, resulting in a spotty blue color, and discoid tension cracks with healed fringes around crystals. Standard temperature heat treatment for corundum happens between 500° and 1700°C, whereas high-temperature heat treatment, such as beryllium diffusion, occurs at temperatures above 1750°C. These high temperatures can modify inclusions in a way that renders them unidentifiable, suggesting that a stone may have undergone beryllium diffusion.
While examining a heated blue sapphire recently, the author observed “smoke ring” inclusions throughout it (see above) using fiber-optic illumination. Trace element chemistry analysis of the blue sapphire via laser ablation–inductively coupled plasma–mass spectrometry revealed no signs of beryllium. This came as a surprise, as this dislocation pattern is associated with beryllium-diffused corundum. These “smoke ring” dislocations are consistent with sapphires that have been heated at high temperatures, but chemistry ruled out beryllium diffusion treatment. This sapphire offers a striking example of why continuous documentation of inclusions, in both treated and untreated gemstones, is an important tool in gemstone analysis.
