gems, corundum, Myanmar.12, Burma.12, Mong Hsu

Smoke treatment is a long-recognized method used to darken the body colour of opal and enhance its play of colour through increased contrast. With careful observation, this treatment can be identified using visual and microscopic features. The following case study documents a particularly clear example. Recently, a parcel of both white and black opals was submitted to the laboratory, declared by the client to be from Ethiopia. All displayed a play-of-colour effect, with the black opals being particularly striking as the vibrant colours stood out against the dark background (Figure 1). Upon closer examination, several features in the black opals drew the authors’ attention. Numerous small, mottled black spots were present throughout the stones. These dark discolourations appeared most prominently around small pits and scratches on the surface (Figures 2 and 3).