The reflectivity of some noble metals alloyed with copper of the formula Cu (x) M1-x , where M is gold, platinum, palladium and silver, has been modelled using only the available optical constants of the pure parent metals, copper, gold, platinum, palladium and silver. The results are compared with experimentally determined reflectivity for some of these alloys and shown to give reasonable approximations, suggesting that the method has utility for the estimation of the reflectivity of alloys when no experimental data are available. The method of estimation of reflectivity has been extended to include two-phase alloys as well as homogenous alloys.