Deposition Pattern of a Pinned Circular Evaporating Coffee Drop

When a coffee drop dries on a solid surface, a ring-like, finite-width stain remains. We establish a simple mathematical model to study the density distribution of the stain across its width. The asymptotic form of the distribution does not depend on the specific evaporation profile, i.e., diffusion-controlled evaporation vs. uniform evaporation. We also compare our findings with the simulation results based on truncated one-dimensional transport process.