1. The process of converting materials into glass or a glass-like amorphous solid which does not have any crystalline structure.
2. In pottery, the point at which a pot loses its porosity during a firing.
3. The progressive fusion of a material during the firing process; as it proceeds, glassy bonding increases and the porosity of the fired product decreases.
4. A forming of a supercooled liquid; such as, glass.
5. The act or process of vitrifying; a state of being vitrified.

When the starting material is solid, vitrification usually involves heating the substances to very high temperatures. Many ceramics are produced in such a manner.

Vitrification also occurs naturally when lightning strikes sand, where the extreme and immediate heat can create hollow, branching rootlike structures of glass, called fulgurites (natural hollow carrot-shaped glass tubes formed in quartzose sand or soil by lightning strikes).

1. The state of being imperfectly vitrified.
2. A substance imperfectly vitrified.