ASM Metals HandBook P10

During the anodic etch, a high acid content, low solution temperature, and high current density will minimize smut formation. Carryover of water into the anodic etching solution should be held to a minimum, and long transfer times after the anodic etch should be avoided. Cold rolled steel that has been subjected to deep drawing and certain prepickled hot rolled steels with glazed brownishcolored surfaces may be exceedingly difficult to clean. For these materials, a solution of 25 to 85 vol% nitric acid has proved effective....