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Glass is a transparent, brittle, solid substance traditionally used in windows, for making bottles and for spectacles ("glasses").
Glass has been made for thousands of years: it is thought to have been first made by the Ancient Egyptians about 5000 years ago.
The production of glass involves heating sand mixed with small amounts of sodium carbonate and calcium and aluminium oxides to very high temperatures.
The addition of sodium carbonate lowers the melting point, somewhat, and makes production easier, whilst the other compounds make the glass more durable - without them, the glass would dissolve in water.
Anne Evans
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