Subsoil: a resource
Glass
The main raw material to produce glass is silicon. Silicon is present in nature inside sand and in some compact rocks (quartzites). The sands that are used are very pure and fine. The materials, pulverized, are heated at 1200 – 1400 °C for a few hours. Then, after a slow cooling, the mass is subject to moulding. The melted mass is moulded and, in order to prevent the product from breaking, it is necessary to gradually cool it down. The glass, completely cooled, is then subject to several refining operations. Glass sheets without flaws can be used to produce mirrors. The reflecting surface can be obtained by applying a thin layer of white metal on the glass: the layer can be made of silver for precious mirrors, lead for dark mirrors, tin and aluminium for ordinary mirrors.
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