Abstract: A method for electrolytic coloring of anodized aluminum or aluminum alloys in an electrolyte containing metal salts is disclosed, in which the aluminum or aluminum alloy is preliminarily treated in an electrolyte by applying a voltage of substantially positive voltage wave form and, thereafter, the electrolytic coloring is carried out in the same electrolyte by applying an asymmetrical alternating current voltage that the positive voltage is smaller than the negative voltage.

Abstract: Process for reclaiming stannous ion by reducing the same in an electrolyte to stannic ion through a simple operation in a short period of time, which comprises the steps of preparing the electrolyte in an acidic range as required and then adding metallic tin to the electrolyte and heating the mixture to at least 80.degree. C., in order to reduce the stannous ion oxidized in the electrolyte containing tin salt to obtain a stable electrolyte treated product. This process may be utilized particularly for effectively reducing and reclaiming an electrolyte which contains tin salt used for electrolytically coloring aluminum.