Relaxation processes and physical aging

Glassy materials have been of service to mankind for centuries, from the earliest soda-lime-silicate glasses to the present sophisticated developments in, for example, metallic, fluoride and superionic glasses. Throughout this time, artefacts have been produced with a very wide range of functions: objects of exquisite beauty, such as the Venetian ‘mille fiori’ ornaments and the stained glass windows of many ancient cathedrals, high technology applications such as optical fibres for communications,‘ smart’ glass for controlled transmission, and slow-release glasses for regulating drug dosages, as well as the more commonplace requirements for containers and glazing. What is perhaps surprising about this remarkable success of glass in general is that the glassy state should still remain today so difficult to define with any precision. Even the seemingly simple question of whether a glass should be considered as a liquid or as a solid remains open to discussion.