RAINBOWs are a relatively new type of high-displacement, piezoelectric actuator produced by selectively removing oxygen from one side of a lead-containing ceramic using a high-temperature chemical reduction process. This process yields devices which contain a piezoelectric layer and a metallic layer (i.e., the reduced layer). In this study, piezoelectric RAINBOW actuators with reduced layer-to-total-thickness ratios ranging from 0.05 to 0.8 were produced from five soft-piezoelectric formulations. The ferroelectric hysteresis properties of each specimen were then measured while taking the total thickness of the device to be ferroelectric. Because of this assumption and the metallic nature of the reduced layer, the resulting coercive field measurements were found to correlate strongly with the thickness of the piezoelectric portion of each device. A simple, non-destructive method for estimating the reduced layer thickness in RAINBOW ceramics was devised based on this relationship.