…(8) the annealer. When a glass vessel is completed it is put inside an annealer, a large insulated box heated by electric elements. The glass is put in at a temperature around 900 degrees Fahrenheit: a temperature at which the glass is no longer moving or glowing hot. Over an eight to twelve hour cycle the glass is brought down to room temperature. Without annealing the internal stresses within the glass will cause it to shatter or explode.