World Of Gems Conference 2017 Proceedings Book

WORLD OF GEMS CONFERENCE V - 18 - SEPTEMBER 2017 and very difficult to detect. Commonly irradiated gems are; • Beryl • Quartz • Chrysoberyl • Rubellite • Diamond • Sapphire • Spodumene • Topaz • Cultured Pearls • Feldspar 5- Heating: Heat treatment creates permanent modifica- tions in the structure of the gem in many cases. The treat- ment is achieved at different levels of temperature and different oxidizing environments depending on the desired effect and the species. The experimentation of heating dif- ferent species and varieties is a regular practice both by gem manufacturers and treatment laboratories. Not all gems can be improved via heat treatment. There are certain species such as emerald or peridot that will not respond favorably to heat. Also, even gems that can be heated, such as sapphires or tourmalines, will not react to heat the same way due to their origin specific features. Definition of low versus high heat is dictated by the mineral rather than the process. While 800°C is very high for aquamarine, it is considered low heat for corundum. The concept of “low heat” is typically pre- sented within the context of the trade as if to imply that the stone has only been “minimally processed” relative to other heated stones. Examples of stones that are known to re- spond well to heat treatment include: • Amber • Tourmaline • Aquamarine • Zircon • Chalcedony • Diamond (LPHT) • Corundum (ruby/sapphire) • Ruby • Demantoid Garnet • Sapphire • Quartz (citrine, etc.) • Spinel • Tanzanite • Zircon • Topaz It is often easier to have proof when a stone has been heated when evidence of thermal alteration is present. It is not al- ways possible to conclusively “prove” that a gemstone has not been exposed to heat, hence the term “No indications of heating.”This term is applied by most gemological labs in re- ports rather than “Untreated.” 6- Diffusion: Diffusion treatment is achieved at extreme heat conditions while additional elements are introduced to the stone. The positive identification of Be-Diffusion is only possible with LA-ICP-MS and LIBS analyses. Ti-Dif- fused sapphires and sapphires with diffused stars are the most common “surface diffusion” products in the sapphire market today. Diffusion treatment is most commonly asso- ciated with: • Corundum • Feldspar (Andesine) PRICING Although meaningful treatment disclosure is by no means universal in the international market, it is widely accepted that a direct relationship exists between the nature of a gemstone and its price. A natural gem (absent treatment) will almost al- ways be priced higher than a comparable looking treated stone. Quality and rarity combine to support the market de- sirability of natural stones. The current record per carat prices at auction for a ruby, sapphire, emerald and jadeite are held by natural (unenhanced) materials. This is, of course, no sur- prise. It does however seem to reinforce that a gem’s value is dependent on more than its visual appearance. When a gem variety has a sufficient population of natural, salable gems, the natural serves as a pricing benchmark. Treated stones of that variety will typically trade at a dis- count from that benchmark. This is evident, for example, in the diamond market. Likewise, when a gem variety is al- most always treated, a natural gem of that variety will typi- cally trade at a premium. This is evident in the emerald market, where a natural (unenhanced) fine quality emerald would be expected to be priced substantially higher than a comparable looking, “oiled” stone. Treatments are used to improve the appearance of both non- salable and salable gem rough. This does have a direct rela- tionship with supply. Although a treatment, when successful, will increase the value of that individual stone, its presence in the market also decreases rarity, and therefore, may de- crease value across the overall population for that variety. In spite of advertisements to the contrary, a treatment does not complete what nature intended. During the past four decades the percentage of treated corundum has more than doubled. Today, it is estimated that approximately 97% of ruby is treated, with the percentage of sapphire and emerald being only slightly less. It is rea- sonable to conclude that visual comparisons between PRICING TREATED GEMS PHOTO 2: Irradiated Blue Topaz. Photo by Gray Roskin.