Abstract: Aluminum, or an alloy thereof, is grained in a two-stage process wherein it is subjected to an electric current while immersed in an acidic electrolyte solution, such as a solution comprised of hydrochloric acid and aluminum chloride. Current density in the first stage of the process is at least as great and preferably substantially greater than in the second stage, while both treatment and time and current consumption in the first stage are less than in the second stage. The process provides a fine uniform grain that is essentially free of pits and is especially beneficial for use in the manufacture of aluminum supports for lithographic printing plates.

Abstract: Improved lithographic printing plates comprise an aluminum support which has been grained in a novel two-stage electrolytic graining process and a radiation-sensitive layer capable of forming a lithographic printing surface. The aluminum support is subjected to an electric current while immersed in an acidic electrolyte solution, such as a solution comprised of hydrochloric acid and aluminum chloride. Current density in the first stage of the process is at least as great and preferably substantially greater than in the second stage, while both treatment time and current consumption in the first stage are less than in the second stage. The process provides a fine uniform grain that is essentially free of pits. Any radiation-sensitive layer is suitable, which after exposure and any necessary developing and/or fixing provides an area in imagewise distribution which can be used for printing.