Structural glasses are produced by many different techniques, such as deposition form the vapour phase in CVD-processes, electrolytic deposition from liquids, irradiation of crystalline solids by particles or by cooling of melts. Cooling of melts is still the most important process to produce glass. Many different criteria have been published on the question under which circumstances cooling of a melt results in a glass or in a crystalline solid. However, this problem does not seem to have been solved yet, since the criteria do not apply in full generality, but rather to special compositions. Such criteria have to explain the formation of oxide, fluoride, chloride, chalcogenide glasses as well as sulphate and nitrate glasses and vitreous phosphorus and sulphur or metallic glasses, notwithstanding the large number of organic glasses.
