Composite films of copper and aluminum were deposited by reactive direct current co-sputtering of copper and aluminum. Varying the number of copper pieces during deposition made it possible to vary the composition of the films. In order to understand the optical behavior of the coatings, the transmittance and the near normal reflectance spectra in the 300-2500nm wavelength range are fitted with model dielectric functions. Valuable information regarding the surface roughness layer and its thickness are obtained. The thicknesses of the layers obtained by modeling were confirmed by surface profilometry. The extracted optical constants by the model were compared with calculations from Maxwell-Garnett, Bruggeman and incremental Maxwell-garnett effective medium theories. The XPS studies done on the samples reveal that the number of copper pieces used during co-sputtering control the formation of copper oxide.