The oxidation process of the Pb-0.08 wt.% Ca-1.2 wt.% Sn alloy was investigated by in situ spectroscopic ellipsometry measurements, combined with electrochemical measurements. The evolutions of the electrochemical and optical parameters show a mechanism of the film growth in two parts. In the first 10 min, the ellipsometric spectra exhibit large variations, whereas the measured current is approximately 0.3 mA cm(-2). During this complex step, the surface topography is continuously changing. This stage corresponds to the growth of lead sulfate crystals, which is then oxidized in a thin and flat PbO2 layer, as confirmed by ex situ X-ray diffraction and scanning electron microscopy analysis. The second part is identified by a rapid and important decrease of the current, down to a low and steady value of approximately 0.01 mA cm(-2). At once, the optical spectra vary slightly. A duplex layer model has been used to interpret spectroscopic ellipsometric measurements. The upper layer is likely composed of beta-PbO2 as suggested by ex situ X-ray diffraction analysis. This model indicates a total thickness of the film approximately 480 nm at the end of the polarization (24 h). (C) 2003 Elsevier B.V. All rights reserved.