Process for roughening support material for printing plates

A support material made from aluminum or an aluminum alloy for printing plates has a prestamped surface. The prior stamping comprises hemispherical indentations with a diameter of from 2 to 50 m and a mean diameter of 20 to 30 m. This support material is electrochemically roughened in an electrolyte which is selected from the group consisting of hydrochloric acid, nitric acid, sulphuric acid and chloride or nitrate ions of an aluminum salt. The current density of the alternating current is 30 to 45 A/dm 2 . The surface roughness R A after roughening is uniform, covers the entire area and lies in the range from 1.0 to 1.5 m.