The reduction of ultrasmall colloidal covellite (CuS) has been examined using 1,1＇-bis(sulfonatopropyl)4,4＇-bipyridinium radicals (ZV(-)) over the pH range 2.5-10. The corrosion process using this reductant is a one-electron-transfer process, producing colloidal Cu2S and H2S. It was observed that this process is partially reversible upon exposure of the irradiated sample to either elevated temperatures or air. In addition, at pH 2.5, the reaction was further complicated by the formation of molecular H-2. At pH 9 +/- 1 the reaction between ZV(-) and CuS ceased to be favorable.