The electrochemical oxidation of a gold electrode supported on an AT-cut quartz crystal in aqueous sulfuric acid resulted in formation of a thin film of gold oxide, and removal of the applied potential led to loss of the oxide. The piezoelectric substrate allowed in situ determination of changes in the potential and the mass of the electrode throughout both processes. Upon opening the circuit (OC), the electrode potential immediately dropped to that characteristic of Au/Au2O3 and remained there until the oxide had been lost. Electrochemical quartz-crystal microgravimetric (EQCM) measurements revealed that the resonant frequency of the crystal behaved similarly, quickly adjusting to a value consistent with approximately a nanometer of Au2O3 and then remaining approximately constant until both the potential and frequency adopted bare-gold values. Reduction of the oxide during the period of constant OC-potential and mass confirmed the onset of cathodic silence -inaccessibility of the oxide to reduction by an applied cathodic potential. (C) 2017 The Electrochemical Society.