Some light on glass

GT V20 1979149-178

The history of glasses whose properties are changed, permanently or reversibly, by exposure to light will be traced. lt begins with the phenomenon of solarisation in soda-lime glasses, with attendant chanye of colour.
Enhancement of this reaction by compositional development produced the family of photosensitive glasses. Special compositions within this general field, coupled with defined heat treatments, made possible the 'Fotoform' materials, which are chemically machineable, and the 'Fotoceram' materials, which are highly crystalline. The latest in this series are the polychromatic glasses, in which a full range of colours has been achieved. Glasses in an entirely different compositional area will
react reversibly to irradiation; these are the photochromic glasses. The opposite effect is also possible: The properties of the light are changed by the material; magnetooptic glasses and electrooptic glass ceramics are examples.