We performed the experiments with the "Tracker" instrument from Teclis Scientific. In practice, due to differences in density, we used the rising-drop configuration; this is obtained by using a curved syringe, allowing to create an oil drop rising within a water phase. The typical size of the drop is 1 mm and the typical volume is of the order of 10 µL. The surface tension is then obtained by fitting the shape of the curve by the Young-Laplace equation.