Development and application of a mathematical model to explain fading rate inconsistencies observed in light‐sensitive materials

Light fastness tests conducted on several areas of a light‐sensitive material may sometimes show inconsistent fading rates. These different fading behaviours suggest that colorants are not evenly distributed over the substrate surface or may be attributed to texture variations of the material. A mathematical model has been developed to help explain these discrepancies. Micro‐fade testing, a relatively novel technique, has allowed microspectroscopic detection of variations in the initial colour parameters of a sample, permitting assessment of its diverging fading rates. The method has been applied to fading data of various light‐sensitive materials resulting in more consistent fading patterns. It has been demonstrated that micro‐fading curves obtained for the same material are related by a constant value, which is the ratio of adjusted values of time and ΔE*.