A nickel thin film is deposited onto a float glass substrate by means of an autocatalytic reducing reaction in a metallizing solution. The growth of this film is monitored in situ using an ellipsometer. By analysing the ellipsometric measurements, the changes in the complex optical index and the thickness of the film over time can be determined. A comparison of the complex optical index obtained from analysis of the experimental results and those predicted by various effective medium theories indicates that the Maxwell-Garnett theory is the best for modelling the optical properties of the nickel layer.