Abstract: A method for producing a water developable lithographic printing plate which comprises treating at least one surface of a metal sheet substrate with a layer of a lithographically suitable, light sensitive, water soluble substance and subsequently coating the thus treated base sheet with an upper layer of a water insoluble, ink receptive, lithographically suitable photosensitive composition. Said photosensitive layers must be either both positive working or both negative working. Upon imagewise exposure through a mask by standard methods the exposed areas of said upper photosensitive composition are alternatively characterized as either water permeable or water impermeable and the unexposed areas are alternatively water impermeable or water permeable as opposed to the exposed areas. Upon said imagewise exposure, the exposed lower level areas in a negative system are rendered water insoluble whereas the exposed lower level areas in a positive system are rendered more water soluble than the unexposed areas.

Abstract: A method for preparing aluminum based lithographic printing plates which comprises treating at least one surface of an aluminum base sheet with an interlayer composition, thereafter anodizing the thus treated aluminun surface, optionally retreating the coated, anodized aluminum plate with another stratum of the interlayer composition and then applying to said surface a suitable light sensitive composition to yield the desired photosensitive lithographic printing plate of improved characteristics.

Abstract: A method for preparing aluminum based lithographic printing plates which comprises coating at least one surface of an aluminum base sheet with a potassium zirconium fluoride solution, thereafter treating the coated, aluminum plate with a stratum of a sodium silicate solution and then applying to said surface a lithographically suitable light sensitive composition to yield the desired photosensitive lithographic printing plate of improved characteristics.