The main constituents of glass are silica, sodium or potassium carbonate, lime, manganese dioxide, cullet and colouring materials.
1. Silica
Silica is the principal constituent of glass. Silica alone when fused at a very high temperature would give a good glass on cooling. However, it is essential to add some quantity of alkaline materials along with lime to make the molten silica glass sufficiently viscous so as to get good workability and resistance against weathering agencies.
2. Sodium or Potassium Carbonate
It is an alkaline material which is also an essential component of glass. This is being added in certain proportion so as to reduce the melting point of silica and to impart viscosity to the molten glass.
3. Lime
This is added in the form of chalk so as to impart durability to glass. In order to make the glass bright and shining, lead oxide is added in place of lime.
4. Manganese Oxide
This is added in certain proportion so as to correct the colour of the glass due to the presence of iron in raw materials of glass.
5. Cullet
Cullet is the old broken glass of the same type as that is intended to be manufactured.
6. Colouring Substances
At the time of manufacturing a coloured glass, a suitable colouring substance is added at the fusion stage to provide the desired colour to the glass.
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