Photomicrography > Corundum > Cobalt glass-filled sapphires
First draft: May 15th, 2014 | Last update: March 18th, 2016
Diagnostic Features of Glass-Filled Sapphires
Cobalt (Co) Glass
Although originally (in 2007) named Super Diffusion Tanusorn, these sapphires are not diffused at all. Instead, their fractures were filled with cobalt (Co) glass. As blue sapphires are coloured by ferrous iron (Fe2+) - which quenches fluorescence - no reaction is expected under a Chelsea filter. But the filler does react.
This reaction should be carefully observed, because some blue sapphires - especially some from Myanmar and Sri Lanka - also tend to contain some chromium (Cr) which causes a uniform colour reaction under the Chelsea filter. But in case of the Supers, it is actually only the filler that causes a reaction.
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Legend: FoV: Field-of-View; DoF: Total focusing depth; DF: darkfield; Obl: oblique illumination (fiber optics); Refl: reflected light; Pol: polarising filter before objective; Sh: shadowing; TM: transmitted illumination, UVL: long-wave ultra-violet radiation; UVS: short-wave ultra-violet radiation; X-Pol: crossed polarising filters