Glasses appear on the earth as a result of cataclysmic events occuring during earth formation. The glass does'nt show an ordered atomic structure like crystals. It is represented as a loosely packed and randomly organized network of spheres ( the O2- anions ) among which are located small ones ( Si4+,Al3+, Na+,…cations).

Nowadays , beside its domestic use , the glass has a real interest for the scientific community. Nevertheless, even though it was used since about 4 millenniums it remains a material difficult to define perfectly .