Glass is created when sand is heated at extremely high temperatures along with soda ash and limestone. Other minerals and additives may be combined into the molten glass to alter the properties of the finished product.
Glass occurs naturally in the form of obsidian at the mouth of a volcano, but mankind began manufacturing glass as early as 4000 B.C. Modern glass is created in furnaces that burn at temperatures of 1700 degrees Celsius. Molten glass is then manipulated to form windshields, glass panes and other products. The rate at which the glass cools affects the physical properties of the finished product.