Glass manufacturing basically takes place by lowering the melting point of silica sand (“vitrescent” material par excellence, which supplies silica able to produce the disorderly, amorphous lattice that characterises the vitreous structure) from about 2000 °C to values close to 1500 °C through the addition of “flux” elements such as soda and potash. The production process also requires the addition of “refining” agents such as sodium sulphate, which facilitates the expulsion of gas bubbles from the molten material and improves the homogeneity of the glass, and “stabilisers”, such as calcium carbonate or lime, in order to make the glass structure less alterable (chemically and mechanically) especially by cancelling the effects of soda which, otherwise, would make the glass soluble in water. Calcareous or lime-based products also contribute to lower the melting point of silica.
In modern practice, the continuous optimisation of production processes, geared towards more efficient solutions both from an energy and an environment point of view, has led to a steady improvement in all the work phases including the choice of the best raw materials.
The continuous search for materials capable of reducing energy requirements in the melting phase and, at the same time, minimising emission in the atmosphere of gases resulting from the melting process has therefore made the use of calcined products increasingly present instead of the traditional lime products . This is the case of the use of lime which is, nowadays, increasingly preferred to calcium carbonate for the well-known advantages that this substitution brings to the glass-making process: lime, whether calcium or dolomitic, which has an increased reactivity compared with the corresponding carbonate (lower melting time), makes it possible to obtain considerable energy savings through a faster fusion process, reduce greenhouse gas emissions (such as, for example, CO2) and, ultimately, increase the overall workability and quality of the finished glass (minor structural defects) by minimising infusions and bubbles.
Commencing with the experience of glass fibre manufacturers, subsequently extended to manufacturers of other types of glass (flat, hollow, etc.), lime is now widely used and is considered an irreplaceable raw material in modern glass-making activities.