This paper reviews the different formulations suggested by the literature for computing the theoretical values of the viscosity of soda-lime industrial glass as a function of temperature and chemical composition. By means of a comparison with the experimental results obtained by the SSV laboratory, it appears evident that the most reliable mathematical model is that proposed by T Lakatos, based on the Vogel-Fulcher-Tamas equation. For a given glass, the theoretical viscosity-temperature curves computed using this formulation are practically indistinguishable from those obtained by interpolating experimental data. The Lakatos model can be coded in a computer program which can also be used for estimating the role of viscosity within the whole forming cycle.
