Vitrification is a process of converting a material into a glass-like amorphous solid that is free from any crystalline structure, either by the quick removal or addition of heat, or by mixing with an additive. Solidification of a vitreous solid occurs at the glass transition temperature (which is lower than melting temperature, Tm, due to supercooling). 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 may also occur naturally when lightning strikes sand, where the extreme and immediate heat can create hollow, branching rootlike structures of glass, called fulgurite. When applied to whiteware ceramics, vitreous means the material has an extremely low permeability to liquids, often but not always water, when determined by a specified test regime.

The microstructure of whiteware ceramics frequently contain both amorphous and crystalline phases. When sucrose is cooled slowly, the result is crystal sugar (or rock candy), but, when cooled rapidly, the result can be in the form of syrupy cotton candy (candyfloss). Vitrification can also occur when starting with a liquid such as water, usually through very rapid cooling or the introduction of agents that suppress the formation of ice crystals.

Additives used in cryobiology or produced naturally by organisms living in polar regions are called cryoprotectants. Arctic frogs and some other ectotherms naturally produce glycerol or glucose in their livers to reduce ice formation. When glucose is used as a cryoprotectant by Arctic frogs, massive amounts of glucose are released at low temperature, and a special form of insulin allows for this extra glucose to enter the cells.

When the frog rewarms during spring, the extra glucose must be rapidly removed from the cells and recycled via renal excretion and storage in the bladder. Arctic insects also use sugars as cryoprotectants. Arctic fish use antifreeze proteins, sometimes appended with sugars, as cryoprotectant.

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