1 INTRODUCTION

THE TEXTILE AND PAINT INDUSTRY today is able to carry out extensive color-matching computations which, through measurement and analysis of the spectral reflectance data of pigment mixtures, can be used to predict the types and ratios of pigments that will yield the particular color under consideration.1 Some years ago, the thought occurred to us to follow the fading of opaque paints based on a fugitive colorant in mixture with a photochemically-inert high-scattering white pigment by computing, at each point in time, the concentration of colorants necessary to match the faded condition.2 Thus, through the use of modern “color-matching” computations, the change in concentration of the fugitive colorant with time can be determined and from thence, an analysis of the rate of fading can be accomplished from the point of view of chemical kinetics. The results of a study of the rate of fading of alizarin lake (C. I. Pigment Red 83, No. 58000; Ciba-Geigy X686) in mixture with titanium white (C. I. Pigment White 21; DuPont Ti-Pure� R-960) in a poly(vinylacetate) vehicle during exposure in an Atlas Electric Devices (Chicago, Ill.) xenon-arc Fade-ometer� have been reported earlier in this journal.2 Microscopic examination of cross-sections of the test paints revealed that in this paint system applied at complete hiding, fading took place on the upper surface of the coating in a zone which varied in depth from about 4 to 20 micrometers, depending upon the pigment volume concentration (PVC) and the concentration of the principal light-absorbing pigment. We have previously reported similar depths of the faded zone in other paint systems.3