Ferroelectric potassium nitrate has been found, by a pulse‐testing technique, to show a threshold electric field, essentially invariant with duration, below which KNO3behaves as a completely elastic dielectric. Test results on several ferroelectric materials, all single crystals, are shown and compared to the results obtained from fused layers of KNO3. The technique for the detection of a threshold is described and the test circuit for obtaining the required data on change in charge vs applied step voltage is included. Finally, a precise time‐independent description of KNO3polarization reversal over the entire range of applied step fields is given by two empirically derived equations, each covering one side of threshold.