- 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.
Glass Facts
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