An automated process, and a device for implementing the process, for preparing a printing block from a photopolymer plate which has been previously exposed to ultraviolet radiation to convert it into a printing block for flexography or typography, or dry offset. The process includes at least the steps of lowering the plate with its sensitive face down into an etching vat, and then etching the plate by the resultant effect of a reciprocating horizontal movement of plane brushes and a to-and-fro movement of the etching vat in a horizontal direction perpendicular to that of the brushes, with the plate being held in place by gravity during the etching.