The measurement of the surface tension on glass at high temperatures is always troublesome, because of the inherent difficulties of the measurement. Surface tension can not be measured directly but it needs to be computed mathematically from the measurement of other physical properties. Methods like the torsion scale with the platinum ring, or the weight of a drop, which are widely used to measure surface tension on liquids at room temperature, are quite difficult to apply on molten glass. In the glass industry the measurement of surface tension is commonly carried out using the method of the pendant wire, heated with a platinum loop. This method is quite simple and inexpensive, but it suffers of a poor temperature control, beside the fact that it is impossible to carry out the test over a wide range of temperatures. In the last 20 years a new method for the measurement of surface tension gained more and more credit, even though it was conceived more than 200 years ago. The two genius of mathematics Laplace and Young wrote the equation which describes the shape of the separation surface between two fluids as a function of the density of the two fluids and of the interfacial tension. This equation, known as Young-Laplace, can be used to compute the surface tension of a drop of liquid, knowing the density at the temperature of the measurement and analysing the shape of the drop. Nowadays there are several instruments available on the market which perform the measurement of the surface tension based on this principle, but all of them work only up to few hundreds degrees.

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