Abstract: This present invention is directed to a method of etching anodic foil for electrolytic capacitors and provides a method of electrolytically growing a porous oxide mask on a surface of a high purity etchable strip of anodic foil for forming etch tunnels at strategic locations on the foil. Unetched high purity aluminum foil is placed in a prepared electrolyte doped with chloride. By passing current through the foil, a porous oxide mask is formed on the surface of the anode foil, with an optimized pore spacing. This oxide mask is then partially removed with a stripping agent in order to expose the underlying anode foil at the bottom of the mask pores to the etch solution. The mask is not removed completely, and the anode foil is exposed only at the pore sites. The foil can then be etched using a conventional etch solution. Etch pits and tunnels form only at the pore sites.