The present invention provides a process for removing a metal surface oxide from a metallic substance by contacting the metal surface oxide layer with a deterging liquid to introduce electrons into the metal surface oxide in contact with the deterging liquid to dissolve the metal surface oxide, which process is characterized in that a metal piece or carbon piece is immersed in the deterging liquid into which gaseous hydrogen has been introduced and the metal piece or carbon piece is electrically connected to the metal surface oxide on the metallic substance. The metal piece is preferably platinum or vanadium. A preferred deterging liquid is one having a pH of about 5 to 7 and containing a complexing agent.
