III. Calcic-Sodium-Silicone

Mario Moretti


The calcic-sodium-silicone glass (common glass) group is the one most commonly used in glass work production, for sheets for construction, furnishings and vehicles, bottles, table glass etc., and is commercially divided on the basis of white colour (perfectly decoloured), half white, coloured (green, amber...).
Calcium oxide, which in the vitrifiable mixture does not exceed, in weight, 12-13%, is, partially, substituted by other bivalent oxides when glass with particular chemical-physical properties is required.
Magnesium oxide (MgO), in addition to improving meltability and workability of the glass, reduces the tendency of denitrification.
Barium oxide (BaO) improves workability, gives shininess and influences the dielectric and electrical resistance characteristics of the glass.
Zinc oxide (ZnO) reduces the expansion coefficient and improves the chemical resistance of the glass.
It is used in compositions of opal glass and in cadmium sulphur-selenide coloured glass in which it is critical for the development of the colour red.
Lastly, alumina (Al2O3), added to glass instead of silica, acts on the viscosity, the expansion coefficient and the mechanical and chemical resistance of the glass.