Colour properties of barrier anodic oxide films on aluminium and titanium studied with total reflectance and spectroscopic ellipsometry

Colour properties of barrier anodic oxide films on Al and Ti are studied. The anodised systems are described using the L*a*b* scale, total reflectance (TR) and spectroscopic ellipsometry (SE). SE is performed in the visual wavelength range and allows simultaneous determination of thickness and refractive index of the anodically formed oxide film. Subsequently SE results predict TR well and prove that the colours are obtained from interference effects. Anodised Ti shows much higher colour saturation than anodised Al. The difference in colour appearance is explained in terms of different reflectance of both metals; it depends less on the difference in refractive index of the oxides.