Erosion process for generation of offset masters

An improved lithographic printing plate includes a substrate layer of a nonconducting, hydrophobic polyester, an intermediate film of conducting, hydrophilic material such as aluminum and a top protective film of relatively hard hydrophilic dielectric material, such as aluminum oxide. A printing image is formed in the lithographic printing plate by an electroerosion process wherein erosion electrodes are pulsed with voltage to break down the dielectric in areas adjacent to the erosion electrodes and to evaporate or otherwise remove corresponding portions of the conducting film, thereby creating holes that extend through the dielectric and conducting films and that expose portions of the surface of the underlying hydrophobic substrate.