Float glass

Instead of drawing the glass substance upwards vertically it is poured out over a bath of floating tin. This produces a totally flat sheet that is cut and cooled. This is the method used by most glass manufacturers today.

Ecological aspects of glass production

The reserves of raw material for glass production are rich, even if deposits of quartz sand are regionally limited. Accessible reserves of the metallic oxides necessary for colouring or covering energy glass -most often tin and gold - are generally very limited. The most important environmental factors are the high energy consumption in production, plus the energy related pollution. Material pollution from quartz dust and calcium chloride can occur. When tin oxide is applied as vapour, hydrogen chloride and hydrogen fluoride are emitted, in addition to tin pollution. Gold film emits less pollution than tin.

Glass does not produce pollution in use, but both antimony trioxide and arsenic trioxide can seep out after disposal, causing environmental pollution. Coloured glass and metal-coated glass may contain heavy metal pigments that can be washed out, and need controlled disposal.

Clear glass is well suited for recycling. The production of new glass can in principle use up to 50% recycled glass. Recycled glass can also be used in the production of glasswool and foam glass. Laminated glass and glass covered with metal film cannot be recycled as window

From the Coptic church in Cairo. Coloured glass is made by adding metal oxides to the molten glass; gold for red, cobalt for blue and copper oxides for green.

glass. All types of glass can however be ground and used as filler in elastomeric roof coverings and in the manufacture of bricks and tiles, as well as for high quality aggregate in asphalts and concretes. Because of a high content of silicon dioxide glass can probably also be used as pozzolana in cements.

Production of glass has become sophisticated and technology dependent, and requires high investment. It is difficult to imagine that a small plant for local production of perhaps one ton per day could be competitive in both price and quality. For glass with a lower standard of translucency and clarity it should be possible to set up local production based on casting recycled glass.

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