This invention relates to the etching of aluminum electrolytic capacitor foil using alternating current and several passes of equal duration alternating with periods of non-etching. 
The prior art has shown the interrupted AC etching of aluminum capacitor foil, but such interruptions have been for the purpose of changing electrolytes or electrolyte connections, for an intermediate anodization, or for completion of the etching in a DC stage.  AC etching has been carried out also in a series of tanks with the foil acting as one electrode. 
It is desirable to have many etch sites per unit area of foil surface (etch density) without mechanically weakening the foil for subsequent processibility.