Madagascar Sapphire: Low-Temperature Heat Treatment Experiements

from noted Australian gemologist Terry Coldham. In Bangkok he ran into a friend with a parcel of Madagascar sapphire. Mr. Coldham’s friend said he was going “to the burner,” hoping to “sweeten” the color with a low-temperature treatment that would lighten the hue. He indicated that the temperatures they were using were likely below 1000°C. This coincided with the sapphire rush at Bemainty (Perkins, 2016) that produced high-quality blue sapphires (figure 1), ranging from lighter colors with a lower iron content to much deeper blues with a higher iron content (Pardieu et al., 2017). The abundance of blue sapphires from Madagascar being tested at Lotus Gemology in Bangkok, along with rumors of lower-temperature heat treatment (see “Defining ‘Low’ Temperature” below), suggested the need for further study and heat treatment experiments on this material. Our aim was to record the characteristics of Madagascar sapphires and to detect this type of heat treatment.