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Glasomvandling, or glass transformation, is a term used to describe changes that can occur in glassy materials. It covers processes within the amorphous state as well as irreversible changes that introduce crystalline phases. The most commonly discussed aspects are the glass transition, devitrification, and long-term alteration under environmental conditions.

Glass transition refers to the gradual softening of an amorphous solid as temperature rises toward the glass transition temperature (Tg). Above Tg, the material behaves more like a viscous liquid or rubber, and its mechanical and thermal properties change markedly. The transition is not a strict phase change but a kinetic process that depends on cooling history, composition, and heating rate.

Devitrification is the crystallization of glass upon heating or aging, typically occurring when the glass is held at elevated temperatures for extended periods. Crystals form within the amorphous matrix and can alter properties such as hardness, strength, and thermal expansion. Controlled devitrification is used to produce glass-ceramics, where a predictable crystalline phase enhances performance.

Natural glasses, such as obsidian, may also undergo glasomvandling through weathering and hydration, gradually developing microcrystalline textures. In engineering contexts, managing glasomvandling is essential for processing windows, product durability, and long-term reliability of glass components.