An evaporating colloidal particle–laden droplet leaves behind a ring-like residue after drying. We routinely observe this ubiquitous phenomenon for dried coffee drops; thus, it is known as the "coffee-ring effect." As a droplet evaporates, the edges dry faster than the center, pulling fluid—and suspended particles—outward. This creates a dense ring of material at the periphery of the droplet. It's a familiar sight to anyone who's spilled tea or coffee, but for scientists working on coatings and inks, this effect can be frustrating. In many applications, a uniform deposit is far more useful than a ring.