22 LEAD GLASS–FILLED RUBIES GEMS & GEMOLOGY SPRING 2006 em corundum has been a mainstay of the jewelry industry for centuries. The demand for rubies and sapphires has usually outdis- tanced supplies, and for much of history only the very wealthy could afford them. With the discovery of additional deposits during the 20th century, the supply of these gems increased dramatically. However, there continued to be more demand for these beautiful stones than Mother Nature could provide. Thus enters the art of treatment. We use the term art here because many if not most of the treatments were not developed by scientists but rather by exper- imenters who relied largely on luck or trial and error. Many of those who developed these techniques never fully understood the science or the “why” of what they were doing, but they understood the “what” and the “how” very well. Corundum, as a very durable material, lends itself to many treatments. And ruby, being the most prized color of corundum, is often a prime focus of these treatments. Over the years, ruby has been sub- jected to heat treatment to change its color and/or improve its clarity; fracture healing to improve clar- ity and get a higher yield from naturally fractured rough; glass filling of cavities to improve appearance and add weight; and diffusion, dyeing, coating, and synthetic overgrowth, among others. The latest venture into ruby treatments involves an improvement in clarity enhancement. In the past, the fractures in rubies have been filled with oils, which do little to improve apparent clarity, and glasses, mostly silica based, which are better than oils but, in our opinion, still not very effective because of their relatively low refractive index. This newest treatment is based on the same prin- ciple that has been applied to emerald and diamond: use of a filling material that closely matches the refractive index of the host material to minimize the appearance of the fractures. In the case of this new treatment, the results are remarkable (figure 1). This article looks at the introduction of this technique, its identification in ruby, and its response to various durability tests. G IDENTIFICATION AND DURABILITY OF LEAD GLASS –FILLED RUBIES Shane F. McClure, Christopher P. Smith, Wuyi Wang, and Matthew Hall See end of article for About the Authors and Acknowledgments. GEMS & GEMOLOGY, Vol. 42, No. 1, pp. 22–34. © 2006 Gemological Institute of America In early 2004, the GAAJ laboratory in Japan issued a lab alert about rubies they had seen that had large numbers of fractures filled with high-lead-content glass, which made them appear very transparent. Since then, large quantities of this material have reached international markets. This dramatic treatment is not difficult to identify with a standard gemological microscope, since it has characteristics similar to clarity-enhanced diamonds (flash effect, gas bubbles, etc.). However, locating filled cavities in reflected light is more challenging, as the surface luster of the filler is close to that of ruby. The filling material appears to be very effective in reducing the appearance of fractures. Durability testing of a few samples by highly skilled jewelers indicated that the filler was fairly resistant to heat exposure during jewelry repair procedures, but it reacted readily with solvents.