Abstract: In addition to having two lithographic layers of complementary lithographic character, an electrically inscribable lithographic printing blank may be provided with a solid but solvent-removable protective surface layer serving to inhibit spurious abrasion of the underlying layer during inscription of the blank and prior handling and storage. To prepare a printing plate from the blank, an electric current is passed between the blank and an electrical stylus so as to inscribe through the protective layer and immediately underlying layer and expose the bottom layer locally, whereafter the protective layer is removed by treatment with solvent to expose the surface of the underlying layer.

Abstract: The amount of water present on a lithographic printing plate during printing is determined by measuring the amount of water present on a surface which is other than that of the printing plate but which carries an amount of water related to the amount of water present on the printing plate. The surface upon which the measurement is made may be the surface of a control pad mounted on the printing roller in the gap between opposite ends of the printing plate, the surface of one of the rollers of the damp train applying water to the printing plate, or the surface of an auxiliary roller contacting one of the rollers of the damp train applying water to the printing plate. The amount of water subsequently applied to the printing plate may be regulated in dependence upon the amount of water determined as being already present on the printing plate.