Migration, the movement of one component in a matrix of another, is a phenomenon well known in the paper, plastics, printing and other industries. Because of the thin films generally involved, migration over short distances can result in large changes in certain properties. This paper describes the use of a modified interference microscope to measure adhesive distribution in a layer of pigment coating on paper. The modifications to the standard instrument are described. The technique described allows far greater accuracy and precision in the measurement of phase changes than previous visual methods. It may be readily adapted to the examination of other thin films.