Whisky, pretty

Kenneth Chang has an article in The New York Times about some unlikely images:

Ernie Button, a photographer in Phoenix, Arizona, found art at the bottom of a whisky glass. Howard A. Stone, a mechanical and aerospace engineering professor at Princeton, found the science in the art.
Eight years ago, Button was about to wash the glass when he noticed that leftover drops of Scotch had dried into a chalky but unexpectedly beautiful film (photo). “When I lifted it up to the light, I noticed these really delicate, fine lines on the bottom,” he recalled, “and being a photographer for a number of years before this, I’m like: ‘Hmm, there’s something to this.’”
He and his wife began experimenting. The whisky with smoky, peaty flavors, like those from the islands of Islay and Skye in western Scotland, were inconsistent, needing more trial and error to produce the picturesque ring patterns. By contrast, those from the valley around the River Spey, in northeastern Scotland, “seem like they’ll work every time,” Button said. “It takes just a drop or two to create a really nice image,” he said. He started photographing the residues, using colored lights “to give it that otherworldly effect,” he said. He called the series Vanishing Spirits — The Dried Remains of Single Malt Scotch.
Button’s experimentations revealed other liquor insights. A twelve-year-old Scotch made patterns indistinguishable from a more expensive eighteen-year one. Bourbon, the American whiskey made primarily from corn, generally works, too, although not the young ones like Jacob’s Ghost from Jim Beam, which sit in barrels for only about a year. “Any aged whiskey will make these rings,” Button said. However, cognac, a liquor distilled from grape wine, does not dry out in this pretty manner.
After several years of creating these photographic prints, Button was curious about the underlying science of what was going on. (Photography is just a successful sideline for Button. He is a speech therapist. “That is how I got my interest in science and research,” he said.)
He found Peter J. Yunker, then a graduate student at the University of Pennsylvania who had done research on the coffee ring effect, produced when a puddle of coffee dries unevenly, leaving a dark brown stain along the edges. Dr. Yunker, who was busy wrapping up his doctorate before heading to a position at Harvard, was not able to help.
Undeterred, Button typed “fluid mechanics” and “art” into Google. Up popped a list of search results that included Dr. Stone. Button emailed. Stone responded.
“I remember it wasn’t clear what we were looking at,” Stone said. But he was intrigued, even though he is not much of a drinker. “I’m not sure I’d even recognize the taste of whisky,” Stone said. “It seemed a nice question to investigate.”
After buying some single-malt Scotch— Glenlivet, Glenfiddich, and Macallan— he and scientists in his laboratory, including Hyoungsoo Kim, began their research. They were able to create similar rings, and then they started making their own mixtures of particles and liquids to decipher what was happening.
In the coffee ring effect, water drying at the edges is replenished from the center of the droplet, and that fluid flow carries particles to the edge, forming the dark ring.
Dr. Yunker had shown that was not always true. If the particles were shaped like grains of rice instead of spheres, the particles deformed the surface of the droplet, and instead of clumping at the edges, the particles formed a loosely packed network across the top of the liquid and dried evenly.
Yunker does not know of any real-world beverages that exhibit this behavior. “To see a similar effect, these particles would have to be fairly large,” he said.
Stone’s group found that the key difference in whisky is that, unlike coffee, it consists of two liquids: water and ethyl alcohol. The alcohol evaporates more quickly, and as the fraction of water increases, the surface tension of the droplet changes, an effect first noticed in the nineteenth century by an Italian scientist, Carlo Marangoni. That, in turn, generates complex flows that contribute to the patterns Button photographed.
“Here, they actually looked at what happens when you change the fluids that are drying,” said Yunker, who is soon heading to the Georgia Institute of Technology as a physics professor, “and they found some very neat effects”. (That would be neat in the usual sense of “cool and intriguing”, and not as in “I’ll have my whisky neat.”)
Kim notes that the story is even more complicated, because their artificial mixture of water, alcohol, and particles does not quite reproduce the whisky patterns. It appears that whisky also contains a surfactant— a chemical that reduces the surface tension of the droplets— and long stringlike molecules known as polymers, which attach to the glass, providing a template for the brushlike stroke patterns seen in the images. Both the scientists and Button suspect the molecules, as yet unidentified, enter the whisky during the aging process.
Kim presented their findings at a meeting of the American Physical Society’s Division of Fluid Dynamics in San Francisco, California.
The science is not just whimsical. Finding ways to deposit particles evenly can have practical applications, like improved inks for printers. “I wanted to tie it to something that might be more general in the materials sciences,” Stone said.

Rico says that having Glenlivet, Glenfiddich, and Macallan as test subjects is a project he'd like to work on...