Process for electrochemically modifying support materials of aluminum or aluminum alloys, which have been grained in a multi-stage process and use of these materials in the manufacture of offset-printing plates

A process for the manufacture of grained support materials of aluminum or an aluminum alloy for use in lithographic printing plates comprising the steps of:

• (I) mechanically graining the material;
• (II) treating the material;
• (III) electrochemically graining the material in an acid-containing electrolyte
• (IV) treating the material;
• and
• (V) anodically oxidizing the material;
• wherein at least one of the treating steps II and IV comprise cathodic modification of the aluminum support material in a solution of aqueous electrolyte comprising at least one member selected from the group consisting of a water-soluble salt in a concentration from 3 g/l up to the saturation limit and an acid in a concentration from 0.5 to 50 g/l, said cathodic modification comprising the steps of:
• making the grained support the cathode;
• adjusting the pH of the aqueous electrolyte to a value ranging from 0 to 11;
• and
• applying direct current from 30 to 100 A/dm.sup.2 for from 5 to 90 seconds at a temperature ranging from 15.degree. to 90.degree. C. to remove from 0.1 to 10 g/m.sup.2 of material.