Ernie Button is a photographer who, in his quest to join his wife in whisky drinking, started taking photos of his drinks. He noticed that certain types of the alcohol would leave behind complex patterns of rings and others would not. So his curiosity drove him to reach out to experts to find out why.
Button used various combinations of colored lights to show the rings left behind. While doing this project, he discovered that any aged Scotch whisky or American or Irish whiskies would leave the patterns behind, but that moonshine, white whiskeys, and other alcohols he tested (which included cognac and wine). So he did what anyone would do faced with an everyday mystery: he turned to Google.
When that failed to turn up an answer, he reached out to a scientist studying the "coffee ring affect," where the evaporation of a single liquid leaves behind a ring of previously dissolved solids. In coffee, that's water leaving behind coffee grounds. Since his alcohols weren't single liquids, but binary liquids of around 60 percent water and 40 percent ethanol, this didn't apply.
What followed is a lovely example of an amateur's observation spurring scientific research. As explained by Scientific American, Button reached out to Princeton professor Howard Stone, who took up the research:
Stone recruited his postdocs, who began chipping away at the question in their free time. First, they created a whisky proxy composed of the liquor's most basic ingredients, water and ethanol, plus some micron-size particles to reveal the final deposition pattern after evaporation. (A micron is one millionth of a meter, or about 40 millionths of an inch.) "If you want to understand the mechanism, you have to take it apart," Stone says. "So we systematically took whisky apart."
The investigators then used video microscopy to examine the water–ethanol solution's evaporative process but they found that the intricate patterns did not appear. Next, they added a small amount of polymeric surfactant—a compound that lowers a liquid's surface tension, such as a layer of soap or oil that sits between the interface of water and air. Surfactants contribute to a phenomenon called the Marangoni effect, in which a liquid's evaporative flows are driven by variation in surface tension. Still the patterns did not appear. So they added one more polymer. That last addition, it turned out, was key: the elusive whisky ring–like patterns finally formed. "We think that particle deposits are regulated by small polymeric components added in the manufacturing process," Stone says. "Wood materials from barrels, for example, could serve as those components." Without similarly rigorous studies, he adds, it's impossible to know why the other alcohols that Button tested do not leave their own intricate deposition patterns.
Button was surprised and pleased that this professor, who he's never met and never spoke to on the phone, was willing to entertain his questions. Button found his curiosity rewarded and Stone hopes that his team's findings will further the knowledge of binary-liquid particle deposits.
Read the rest of the story and see more of Button's photos at Scientific American.