The first Brazilian Symposium on the Treatment and Characterization of Gems was held at the School of Mines of the Federal University of Ouro Preto, in Minas Gerais, Nov. 5-8, 2000. Brazil’s Minas Gerais state has produced some of the most significant gem finds in the world, including large quantities of gem materials that can be treated to make them more salable. Considering the enormous commercial potential of Brazilian gems, Brazil’s recognition of the importance of disseminating enhancement information is a great relief to many in the jewelry industry.
Irradiation. Approximately 130 people attended the conference, including Alice Keller, editor of the Gemological Institute of America’s Gems & Gemology. On the subject of irradiation enhancement, Keller writes: “One of the problems with commercial irradiation of gems, according to Paulo Rela of the Brazilian Sterilization Co., is that stones from different deposits will respond differently to the same process. Only with careful experimentation can the potential results be determined.” Keller reports that the cost to irradiate gems at the Institute for Energy and Nuclear Research (IPEN) ranges from approximately $10-$50 per kilo of quartz, and roughly $300-$400 per kilo of topaz.
Some of the more commonly irradiated beryls—which are treated using electron and gamma irradiation as well as with heat—are dark blue maxixe beryls created from aqua; green or yellow beryl from colorless beryls; and deep pink morganites from lighter colors. Irradiation also produces orange-yellow body-color opal, various colors of diamond and quartz, blue and yellow topaz, red tourmaline (from pinks), and lavender kunzites (from pale pinks). Unless the gem color fades—as it sometimes does in the maxixe or yellow beryls, for example—there is no easy means of detection. It has been confirmed that gamma irradiation with subsequent heat treatment can produce tourmalines of “golden” yellow, “rubellite” red, and violet. Bench jewelers should be aware that heat greater than 450°C can change these gems to colorless.
Fillers. On the subject of fracture filling, the Brazilian Symposium mentioned only emeralds, says Keller. But tourmalines also are routinely filled, and Brazil produces a lot of tourmaline. Most often, according to lab reports, if you see a filled tourmaline, it’s typically a rubellite or bicolor. These two are commonly fractured and in greater demand than most other colors, with one big exception—Paraíba. (See “Paraíba’s Tucson Connection,” p. 40)
For further information about the Brazil Symposium, see GIA’s “Insider” e-mail newsletter (giainsider@gia.edu ) or the Brazilian Web site (in Portuguese) at www.ufop.br/eventos/ .