Having evolved through several sets of principles over time, the modern technique of hand blown glass involves inflating molten glass with a blowpipe and molding the glass under extremely hot conditions. Three furnaces, which are contained in one often-portable unit, are used in the three-step glass blowing process. Glass is melted at temperatures up to 2400F (1315C) and is let cool slightly to release air bubbles. To mold the glass, it is placed in the second furnace, known as the “Glory Hole,” where its temperature is sustained above 1350F (730C). Annealing, or cooling the glass for its final molding and shaping, takes place in the “lehr.” Take a look at this complicated process. Enjoy.