Window glass is typically made by mixing soda ash (Na2CO3), limestone (CaCO3), and silica sand (SiO2) and then heating to 1500 degrees Celcius to drive off Co2 from the Na2CO3 and CaCO3. The resultant glass consists of about 12% NaO2 by mass, 13% CaO by mass, and 75% SiO2 by mass.