corundum, treatments.6, Burma.12, gems

THE DISCOVERY OF EXTENSIVE RUBY deposits in the Mong Hsu area of Myanmar (Burma) has provided the marketplace with a much-needed source of fine ruby in smaller sizes (see, e.g., Hlaing, 1991; Henn and Bank, 1993; Kammerling et al., 1994). Much of the ruby from this location is characterized by blue or blue-black cores which generally are removed by heat treatment (Peretti et al., 1995). The heat treatment is straight-forward: Temperatures of 900°C or above in an air atmosphere are usually sufficient to accomplish the desired change in color. When substantial quantities of Mong Hsu ruby began arriving at gemological lab-oratories worldwide, new features were recognized that were soon identified as residual flux inclusions (Peretti, 1993; Milisenda and Henn, 1994). These observations were mentioned in grading reports (Hänni et al., 1998), and have initiated a serious debate on the use of flux in heat treatment and, in particular, what the presence of large amounts of flux means in terms of the quality and durability of the original ruby.