Thin film layers of Cr–Au were subjected to temperatures in the range 423–573 K for various periods of time and the morphology of the Cr layer was examined with optical and scanning electron microscopy. A preferential depletion of Cr was found beneath the Au grain boundaries and intergranular spaces which was not fully compensated by diffusion of Au into the Cr. Since the Au grain boundaries intersect, this results in islands of remaining Cr surrounded by a labyrinth of voids or channels. This phenomenon renders the entire Cr–Au interface vulnerable to the entry of corrosives. By using transmission optical microscopy in conjunction with a photometer, the optical transmission of the Cr layer was measured and related to the Cr depletion as a function of time and temperature. From these measurements two mathematical models were devised to calculate the activation energy for the Cr diffusion resulting in values of 1.30 and 1.36 eV, respectively.