The electrical conductivity of glass is a crucial parameter for optimising the electrical boosting or for setting up electric furnaces. It is measured in a calibrated furnace using a pair of suitably shaped Pt electrodes, consisting of a hemispherical cup containing the molten glass and a hemispherical bulb which is immersed inside the molten glass during the measurement. The resistivity of the glass is measured at temperatures between 600 and 1600°C, with the passage of alternating current at various frequencies.