A new effect which allows direct formation of thin metal films of controlled morphology is described. Patterns of glass‐ceramic opal are developed in photosensitive glass samples by UV irradiation and heat treatment. The samples are then ion exchanged in molten salt baths containing Ag+or Cu+ions. On subsequent firing in a hydrogen atmosphere, continuous films with typical thin metal films properties grow on the opal regions of the samples. Discontinuous films, characterized by activated resistivities and switching, grow on the glassy regions.