High Quality Content by WIKIPEDIA articles! The glass-liquid transition (or glass transition for short) is the reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle state into a molten or rubber-like state. An amorphous solid that exhibits a glass transition is called a glass. Supercooling a viscous liquid into the glass state is called vitrification, from the Latin vitreum, "glass" via French vitrifier.