Liquid films formed from a surfactant micellar solution thin in a stepwise fashion (stratify): the film thickness decreases layer-by-layer and dark spots appear (areas of the film with one micellar layer less than their surroundings). In a recent paper [Langmuir 2016, 32, 4837-4847], we presented a twodimensional diffusion model to explain the expansion of the dark spots inside the foam film formed from a nonionic surfactant micellar solution. Here, we apply the model to explain the dark spot expansion in the foam film formed from an anionic surfactant micellar solution of sodium dodecyl sulfate. We also apply this model to explain the expansion rate of the dark spot that makes contact with the meniscus. Our model adequately predicts the experimental measurements. (C) 2016 Elsevier Inc. All rights reserved.