According to Kurt Nassau's book Gemstone Enhancement sapphires treat
from 1500 degree C for extend periods of time all the way to 1900
degrees C. These are very high temps not attainable with ordinary
ovens which top out at approximately 1100 degrees C. Buy Kurt's
book for more info. GIA bookstore can get it for you, or online
somewhere. Hope this helps. ciao,
Steve Green - Rough and Ready Gems www.briolettes.com
Fine gem briolettes and precision ultrasonic drilling.