gems, zoisite, tanzanite, treated tanzanite

Over the past five years, gemologists at Bangkok’s Lotus Gemology have seen increasing numbers of what we might call “non-traditionally” oiled gems. This is particularly true of, but not limited to, Burmese gems such as ruby, sapphire, and spinel. But it is important to note that any gem with surface-reaching fissures can be oiled, often with dramatic improvements in apparent clarity. Cuprian and rubellite tourmalines are also frequently enhanced in this way. Recently we received a faceted tanzanite weighing more than 100 carats for testing. As is our practice for non- emeralds exhibiting fissure-filling clarity enhancement, we photograph the gem and then allow the client to re-submit the stone after filler removal. Figure 18 clearly shows the dramatic effect that fissure filling with oil/resin can have on gems such as tanzanite, even where the refractive index of the filler does not closely match that of the gem.