The high corrosion resistance of amorphous coatings deposited from chromic acid electrolytes containing formic acid, is shown to be caused by carbon incorporated into the coatings, rather than by their amorphous structure. The unusual shape of the voltammograms (no region of active dissolution is present) is attributed to inhibited chromium dissolution, a decreased hydrogen overvoltage, and the formation of a passivating film at the metal surface. The latter factor predominates and controls the corrosive and electrochemical behavior of chromium-carbon coatings.