Glass Facts

  • Glass is made mainly from ordinary sand (composed of silica), from soda ash (sodium carbonate) and from limestone (calcium carbonate).
  • Glass can be made from silica alone. However, silica has a very high melting point (1700°C), so soda ash is added to lower its melting point.
  • Adding a lot of soda ash makes glass too soluble in water, so limestone is added to reduce its solubility.
  • To make sheets of glass, 6% lime and 4% magnesia (magnesium oxide) are added to the basic mix.
  • To make glass for bottles, 2% alumina (aluminum oxide) is added to the basic mix.
  • Very cheap glass is green because it contains small impurities of iron.
  • Metallic oxides are added to make different colors.
  • Unlike most solids, glass is not made of crystals and does not have the same rigid structure. It is called an amorphous solid.
  • When glass is very warm it flows slowly like a very thick liquid.