Abstract: The fading of materials due to light exposure over time is a major contributor to the overall aged appearance of man-made objects. Although much attention has been devoted to the modeling of aging and weathering phenomena over the last decade, comparatively little attention has been paid to fading effects. In this article, we present a theoretical framework for the physically based simulation of time-dependent spectral changes induced by absorbed radiation. This framework relies on the general volumetric radiative transfer theory, and it employs a physicochemical approach to account for variations in the absorptive properties of colorants. Employing this framework, a layered fading model that can be readily integrated into existing rendering systems is developed using the Kubelka-Munk theory. We evaluate its correctness through comparisons of measured and simulated fading results. Finally, we demonstrate the effectiveness of this model through renderings depicting typical fading scenarios.