The viscosity behavior of glass at high temperature is of fundamental importance for crucial aspects of the production process such as melting, refining and forming.

High temperature viscosity is measured in a calibrated furnace exploiting the principle of the rotating rheometer: a platinum rotor is immersed into the molten glass (contained in a Pt crucible) at a given temperature, and the torque required to keep the rotor rotating at a constant speed, which is a function of the viscosity of the molten glass, is measured.