Three different reasons for surface damages of glasses after machine dishwashing

A variety of glass cups has been investigated after treatment in a machine dishwasher. Three types of surface damages were found. The first type consists of clouding oil the inner and outer surfaces appearing after about 1000 washing cycles. It can be related to the long range granular structure of glass, which is believed to be formed by thermal density fluctuation. During washing both water and detergents act as weak etchants, first eroding the smooth glass skin, then revealing the granular structure. As soon as the linkages between the granules are entirely broken by the etching, holes will manifest themselves at these sites. When the size of the holes (the hole width) reaches the half of the light wavelength, light scattering occurs and the glass seems cloudy. The second type is the sheet clouding on the outer surface appearing after about 100 washing cycles. It can be related to holes oil the surface, which are formed by the loss of the sphere domain phase from the SiO2-rich matrix during washing. These domains result from phase separation induced by round-melting of the sharp cutting edge, which is responsible for local clouding of glass. The third type is a golden film on the inner surface. These films are probably formed by complex formation between the glass surface and the organic compounds in the drinks. All of the damages studied here are irreversible.