Abstract: Starting sheets are straightened and stiffened in electrolytic refining plants by shaping the same predetermined areas of the starting sheet surfaces once or several times during successive shaping stages in such a manner that the elasticity range of the starting sheet material is at least in part exceeded. During each shaping stage depressions or grooves deviating from the plane of the starting sheet surface are produced in the starting sheets by shaping the said same areas of the starting sheet surface alternately from the opposite sides of the starting sheet during the different shaping stages, whereby the alternate shaping of the areas of the starting sheet surfaces from the opposite sides of the starting sheet straightens the starting sheet and causes work-hardening in the material of the starting sheet, and the depressions or grooves deviating from the plane of the starting sheet surface cause a stiffening of the starting sheet.