To one U.S. artist and professional photographer, the patterns in the bottom of a glass created by the last drying drops of whisky were attractive for their beauty; to a Princeton engineer, they're attractive for the science behind them.
Phoenix-based artist Ernie Button, who captures beautiful photographs of the stunning patterns formed when a couple of drops of whisky are allowed to coat the bottom of a glass and dry, became curios about the science behind those patterns.
So he contacted Princeton engineering Professor Howard Stone, who suspected science in those patterns, namely a phenomenon linked to surface tension gradient, also known as the "Marangoni Effect."
"It's infinitely fascinating to me that a seemingly clear liquid leaves a pattern with such clarity and rhythm after the liquid is gone," says Button. "Professor Stone and his team graciously entertained my questions and were very helpful with my understanding of this phenomenon."
Stone heads the Complex Fluids Group in the university's Department of Mechanical and Aerospace Engineering, and was intrigued by Button's photographs and that the effect worthy of study.
"My group focused on gaining a better understanding of the composition of whisky, identifying the possible 'suspended material,' and doing controlled model experiments to understand possible shapes and forms of deposits during evaporation," he says.
The crucial quality of whisky in forming the patterns, the researchers suspected, is that it contains two liquids -- alcohol and water -- that evaporate at different rates.
Alcohol evaporates at a quicker rate, and as the ratio of water changes the surface tension of a liquid droplet is modified, an effect first observed by 19th century Italian scientist Carlo Marangoni.
In addition, whisky contains a chemical that acts as a surfactant, further reducing droplets' surface tension, and long molecules known as polymers that apparently fasten to the bottom of the class, creating a template for the brush-stroke patterns in Button's photographs.
Although the researchers have not been able to identify the molecules, they say the suspect they enter whisky during the process of aging.
Whisky patterns in a glass might seem a frivolous subject for scientific research, but the researchers point out that learning to understand and control the depositing of particles in a thin film is central to for many industrial or commercial applications.
The research could yield practical applications like creating improved ink for ink jet printers, and a study of whisky is as good a starting point as any other, Stone says.
"I wanted to tie it to something that might be more general in the materials sciences," he says.
