Constituents in metal alloys and rocks may be seen as different colours using interference film microscopy. The thin films which produce the interfeference colours may be deposited either by vacuum evaporation or reactive sputtering . Tne technique is used in a wide range of investigatons which require identification of phases quickly and easily, e.g. in nickel-base superalloys and hard metals. The theory, techniques for optimising the performance and a method of quantifying the results by microspectrophotometry will be discussed and a case study presented.