TechNotes 4: Heat & Glass
Because of its amorphous molecular configuration, glass reacts to heat differently than do other materials. Whereas metals heated to a specific temperature (a melting point) change from solid to liquid instantaneously, glass goes through a gradual transformation from a material that behaves like a solid to a material that behaves like a liquid.
This transformative phase is what allows us to blow glass, and work with it in the many ways we call “kilnforming”. During this phase, the glass will have a consistency similar to honey. As the temperature of the glass continues to increase, its characteristics will become more similar to liquid. When the glass is again cooled, it will once again feel solid, glass-like, though molecular structure will resemble that of a stiff liquid.
This is why glass is sometimes referred to as a superheated liquid.
Video lesson: Heatwork and Color