Hydrogen atoms are, on an atom-by-atom basis, the most influential constituents of oxide glasses. In the glass structure, these atoms reside in the form of hydroxyl ions bound to the glass-former cation, e.g. silicon, boron, germanium, of phosphorus. No other element has as great an effect on glass properties when concentrations are compared on an atomic basis. This effect is even more dramatic when properties are compared on a weight basis, since hydrogen is also the lightest of all elements. The effects of hydrogen ions, in the form of hydroxyl, on the properties and applications of glasses range from the depression of the viscosity to the enhancement of phase separation and crystallisation rates and to the absorption of light, which is so important for communication optical fibre technology.
