The article discusses the phenomenon of coffee stains appearing darker at the edges due to the dynamics of evaporation and solid deposition. Key points include: - The "pinning" of the contact line is crucial for the formation of the pronounced ring stain. This pinning is influenced by the surface roughness of the substrate. - Higher curvature at the edges causes increased evaporation rates, leading to non-evaporating solids concentrating at the edge, resulting in darker stains once the liquid evaporates. - The article highlights that similar staining phenomena can occur with other liquids, reflecting a broader context in liquid behavior on solid surfaces.