Ever Ponder What’s At The Bottom Of Your Whisky Glass? One Guy Did And Here’s What He Learned

Ever look at the bottom of your whisky glass and wonder how the rings left by your spirit are formed? Neither have I, but photographer and artist Ernie Button did. After a series of striking photographs focusing on the patterns formed after letting a drop or two of whisky coat and dry in the bottom of a glass, Button started looking into the physics behind them as he was fascinated by why “a seemingly clear liquid leaves a pattern with such clarity and rhythm after the liquid is gone.”

Button reached out to Professor Howard Stone and the complex fluids group at Princeton University’s Department of Mechanical and Aerospace Engineering for insight. They in turn began experiments to better understand the composition of whisky and the possible shapes, waves, and marks that the drying process leaves.

The researchers, in a series of controlled video microscopic examinations, compared drying droplets of actual whisky with an alcohol-water solution representative of whisky. What they found, according to the researchers, was that

initially the droplet of alcohol-water solution creates a complex mixing flow. Ethanol evaporates first, due to the lower vapor pressure compared to water and, once the ethanol vanishes, a radial pattern can be observed. Further, as the initial ethanol concentration increases, the mobility of the receding contact line is increased as well. And, at high ethanol concentrations, the contact line recedes and draws groups of particles along with it that are then deposited in a ring-shaped pattern.

The marks are defined by a concept known as the Marangoni Effect, which is the the name given to different forces driven by the surface tension of two liquids. The same concept is also what makes “tears of wine” form in a glass.

“The alcohol-water solution shows circulation flow patterns (triggered by the Marangoni Effect), which occur during drying and influences patterns formed in evaporating whisky solutions,” said Hyoungsoo Kim, a researcher within Stone’s group. “Deposits in the actual whisky come from a small amount of inherent raw materials present from the preparation process.”

In the end there is a lot of science in the rings we wash out if our glasses. And the studies that Mr. Button has started will lead toward better drying and nano technology and untold industrial applications. But, for the most part, I think they are far prettier to look at then to think about. Button does a great job at photographing this phenomenon, and his work can be found at his website. The results of this fascinating scientific work were also presented in late November by Stone and his team at an American Physical Society meeting in San Francisco.