Most jewelry available today includes a gemstone as a focal point for the piece. Sapphires and rubies are just two of the more popular gems used in this way. When mined, the gems are not faceted or ornamental. You must have them cut to bring out their brilliance and beauty. One technique used widely in the industry is to heat treat the gems before cutting or selection for use in jewelry. The process of heat-treating the gems enhances the color of the gemstone. The color deepens and may change slightly. Heat-treating occurs in two stages, the fancy burn and the blue burn. Most sapphires look best after the blue burn stage.
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Place the raw gemstones in a crucible after you thoroughly clean them. The crucible will hold the gemstones in the furnace and avoid mixing them with stones from other sources.
Raise the temperature of the oven to approximately 1,600 degrees Centigrade. Most electric ovens used for this process are computer controlled. The temperature of the furnace remains steady to allow the crystal structure to reorient, resulting in an intensification of the color or the clearing of a cloudy appearance in the crystal. This stage of the heat treatment is the fancy burn.
Allow the gemstones to cool until you can sort them. You need to sort these stones to separate the stones that possess satisfactory color depth.
Separate the acceptable gems from the rest of the gemstones and return the rest of the stones to the crucible and place back in the furnace for a final heating. This second heating is the blue burn and is the process that yields the greatest improvement in appearance to 80 to 85 percent of sapphires.