GEM EDUCATION : Heat-Treating Ruby & Sapphire

Among the various types of gem treatments practiced today, the heat treatment of ruby and sapphire is the most common and most important. Rubies and sapphires heated under certain conditions in order to improve their color and/or clarity, thus increase their value. The results after the heating vary widely and depending upon the type of material, ratio/type of the color-bearing impurities, heat treatment technology, heating method applied, equipment used and other parameters.

The most common heat-treating processes applied to ruby-sapphire as defined by Ted Themelis using his heating technology and methodology developed over the last 20 years as described below:.

Nigerian sapphire before (left) and after (right) heated in our laboratory
Some heat-treating processes of ruby-sapphire as defined by Ted Themelis
#
PROCESS
COMMENTS
BEFORE HEATING
AFTER HEATING
3
 FRACTURE FILLING
 Surface-reaching fissures/cracks and cavities may be filled with additives to improve their clarity, luster and appearance
4 DEVELOP ORANGE Dark/purplish red rubies may turn orange to golden-orange, specially when beryllium is used as additive in the process.
9

 INTENSIFY YELLOW, DEVELOP ORANGE
 Pale yellow sapphires may be intensified to deeper yellow, or may turn orange/yellow and other colors. When beryllium and other additives are used the color improvement is dramatic.
10 DEVELOP BLUE

 Milky-silky (geuda) or partially blue ("ottu", "ural") and other types of corundums may turn to near-uniform blue.
18

 SURFACE/SUBSURFACE COLOR DIFFUSION Lab prepared additives heated with selected natural, synthetic, or previously treated corundums may produce near-uniform blue, pink, orange, orange-pink coloration. The color is confined at/near the surface/subsurface of the stone.
To learn more on the above heat-treatment processes (plus 14 more) please refer to the books The Heat Treatment of Rubies & Sapphires ( pp. 21-22), Beryllium-Treated Rubies & Sapphires and Flux-Enhanced Rubies & Sapphires, all written by Ted Themelis. For those individuals seriously interested in this subject, they may consider to enroll in our training course on heat-treating ruby & sapphire, offered exclusively from our laboratory in Bangkok.To view images of some gem treatment equipment click here
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