Table 1 The six types of glass surface described by Hench and Clark (1978).
Type I | Formation of a thin hydrated surface layer with no significant difference with the bulk glass. Stable glass. |
Type II | Formation of a silica rich protective film due to the exchange of selective alkali ions, with no further damage to the silica network. |
Type III a | Formation of two layers of protective surface film of aluminium silica or calcium phosphate on top of a silica rich layer. |
Type III b | Formation of multiple layers of hydroxides or oxides on the glass surface when exposed to water, especially on alkali borosilicate glass. |
Type IV | Formation of a silica rich non-protective film when the silica concentration in the glass composition is not high enough to prevent loss of alkali or destruction of the silica network. Unstable glass. |
Type V | Formation of soluble glass with silica dissolution and equal loss of alkalis. |
