Physicist Mathieu Souzy of the University Twente joined colleagues for an evening of pasta and board games, sparking a conversation about how adding salt to a pot can create a white ring on the bottom. Intrigued by this phenomenon, they sketched an experimental protocol and set out to investigate.
According to their new paper in Physics of Fluids, three factors contribute to forming the perfect circular pattern: particle diameter, settling height, and the number of particles released at once. The smaller the particle diameter, the more efficient the ring formation.
This concept is similar to the “coffee ring effect,” where evaporation creates a ring around coffee grounds as liquid evaporates faster at the edge than the center. However, large drops can produce less uniform stains by mixing solvents with water or alcohol.
The researchers also explored other unique patterns formed by droplets, such as whiskey webs and colorbreaks in paint. These variations occur due to differences in brand characteristics, like a “fingerprint” for each type of whiskey.
For their experiments, Souzy et al. used a large transparent water tank to minimize external effects. By understanding the mechanisms behind salt ring formation, physicists hope to unlock the secrets of other deposit shapes and identify key parameters involved.
Source: https://arstechnica.com/science/2025/01/how-to-get-a-perfect-salt-ring-deposit-in-your-pasta-pot