Wikipedia says this...
The transformation of raw materials into glass takes place around 2400°F (1315°C); the glass emits enough heat to appear almost white hot. The glass is then left to "fine out" (allowing the bubbles to rise out of the mass), and then the working temperature is reduced in the furnace to around 2000°F (1100°C). At this stage, the glass appears to be a bright orange color. Though most glassblowing is done between 1600–1900°F (870–1040°C), "Soda-lime" glass remains somewhat plastic and workable as low as 1350°F (730°C). Annealing is usually done between 800–900°F (430–480°C).
Glassblowing involves three furnaces. The first, which contains a crucible of molten glass, is simply referred to as "the furnace." The second is called the "glory hole", and is used to reheat a piece in between steps of working with it. The final furnace is called the "lehr" or "annealer", and is used to slowly cool the glass, over a period of a few hours to a few days, depending on the size of the pieces. This keeps the glass from cracking due to thermal stress.
Good luck...
Peccavi, January 2010
