A brief short circuit is not sufficient to relax the entire spectrum of the stress accumulated in an insulator during a long time polarization. Following neutralization, a return voltage appears. This phenomenon is used as a routine characterization tool in some areas of electrical engineering. Several experimental results are detailed here supporting the interest of this electrostatic technique as a laboratory characterization tool. For instance, the sensitivity of this technique may be applied to follow the ageing of cables for the aircraft industry, as well as to monitor interfacial polarization build-up at high temperature on polarized alumina plates. It has also been used to demonstrate a photoelectret effect on polyimide films, which is described. We analyze here the diverse physical processes that may be responsible for return voltage: slow dipolar relaxation processes, interfacial polarization, heterogeneous conductivity and injected space charge motion.