Nevertheless, the production of fused silica glass is quite a large industry; it is manufactured in various qualities, and, when intended for optical purposes, the raw material used is rock crystal rather than quartz sand.sodium carbonate (soda ash), which makes available the fluxing agent sodium oxide.By adding about 25 percent of the sodium oxide to silica, the melting point is reduced from 1,723 to 850 °C (3,133 to 1,562 °F).High-purity, ultratransparent oxide glasses have been developed for use in fibre-optic telecommunications systems, in which messages are transmitted as light pulses over glass fibres.When ordinary glass is subjected to a sudden change of temperature, stresses are produced in it that render it liable to fracture; by reducing its coefficient of thermal expansion, however, it is possible to make it much less susceptible to thermal shock.
Millefiori glass, for which the canes are cut in such a way as to produce designs reminiscent of flower shapes, is a type of mosaic glass. As early as the 13th century the Venetian island of Murano had become the centre for glassmaking.
Ferric oxide gives a yellow colour but requires an oxidizing agent to prevent reduction to the ferrous state. Selenites and selenates give a pale pink or pinkish yellow. Nickel with a potash–lead glass gives a violet colour, and a brown colour with a soda–lime glass.
Copper gives a peacock blue, which becomes green if the proportion of the copper oxide is increased.chalcogenide glasses, which are selenides, containing thallium, arsenic, tellurium, and antimony in various proportions. Their photoconductive properties are also valuable. Certain metallic glasses have magnetic properties; their characteristics of ease of manufacture, magnetic softness, and high electrical resistivity make them useful in the magnetic cores of electrical power transformers.
Glass, an inorganic solid material that is usually transparent or translucent as well as hard, brittle, and impervious to the natural elements.
Glass has been made into practical and decorative objects since ancient times, and it is still very important in applications as disparate as building construction, housewares, and telecommunications.
Other materials are also added, some being put in to assist in refining the glass (i.e., to remove the bubbles left behind in the melting process), while others are added to improve its colour.