Some experiments by ordinary turntable methods have been made on the charging of ZnO-resin layers by negative, positive, and combined negative and positive (N-P) corona ions. Some mechanisms and theories of corona charging were clarified from the analyses of various experimental data such as the

characteristic curves of samples, the

characteristic curves of corona chargers and samples, and the variations of corona current and surface potential during the process of corona charging. Experiments on image reversal by the (N-P) corona-charging process were also tried, and some reversal images of fairly good quality were obtained by this method.