ABSTRACT
The word glass applies more to a physical state of the matter than to a chemical composition; in fact the composition of glasses can be quite different, according, for instance, to their color, to thermal or mechanical resistance (see Table 7.1); glasses can be made from phosphates, aluminates, borates, or inorganic halides (a ionic compound containing a halogen), and the name glass is attributed even to special forms of organic material [2]. Among several definitions of glass, the oldest perhaps belongs to Eraclito (a Greek philosopher of the 5th century B.C.) who stated that glass was an artificial stone, produced by fire. More accurate scientific definition was proposed by ASTM in 1999 [3], according to which, glass is an amorphous, inorganic product of fusion that has been cooled to a rigid condition without crystallizing; glass is also indicated as a super-cooled liquid. Glass is also a subclass of ceramic materials i.e., inorganic, nonmetallic materials. Some ceramic materials (china, porcelain, ceramic, etc.) are also used for packaging functions; to them, however, just a few notes will be reserved in this chapter. Therefore this chapter deals, prevalently, with what everybody knows as glass (mainly a silicate glass, often named as soda-lime glass). All the different definitions of glass tend to emphasize the physical state of this material which deserves to be described and well understood.
