Beautiful art from used glasses of Scotch (Plus some nifty fluid mechanics)

After you drink some Scotch, there's usually a thin film of the liquor left clinging to the bottom and sides of the glass. If you leave it out overnight, it'll dry and be a pain to wash off in the morning. But the same dried booze leavings can also be the beginnings of some really lovely art.

Ernie Button takes photos of the waving, swirling patterns left behind on Scotch glasses. This one — part of a series called Vanishing Spirits — is a picture of glass that once held a nice measure of Balvenie.

The idea for this project occurred while putting a used Scotch glass into the dishwasher. I noted a film on the bottom of a glass and when I inspected closer, I noted these fine, lacey lines filling the bottom. What I found through some experimentation is that these patterns and images that can be seen are created with the small amount of Single-Malt Scotch left in a glass after most of it has been consumed. It only takes a very thin layer of Scotch to create; the alcohol dries and leaves the sediment in various patterns. It’s a little like snowflakes in that every time the Scotch dries, the glass yields different patterns and results. I have used different colored lights to add 'life' to the bottom of the glass, creating the illusion of landscape, terrestrial or extraterrestrial.

Interestingly, there was a recent article that was published in the Journal of Nature (I think) by Dr. Peter Yunker on the Suppression of the Coffee-Ring Effect by Shape-Dependent Capillary Interactions i.e. how are coffee rings made. I contacted him to see if he could see any obvious connection between the two liquids and the rings / patterns they create. He got back to me and unfortunately could not explain what was happening with the Scotch.

That paper Button mentioned was published in 2011. It explores the physics of particles suspended in liquid — not just coffee, but lots of things. Turns out, if you put a drop of liquid on a solid surface, it will tend to dry in a circular shape. As it dries, anything suspended in the liquid will migrate to the outside of the circle. If you put a drop of coffee on a table and leave it to dry, what you'll get is a round spot ringed by a narrow band of dark coffee gunk.

Why does the gunk form a ring, instead of evenly covering the whole circle? Yunker's research showed that it has to do with the shape of the particles that make up the gunk.

In this video, you can see those microscopic particles and how they behave.

The video is divided into five parts.

In the first, you can watch a "coffee ring" form, as spherical particles move toward the outside edge of a drop of liquid and stick there.

In the second part, ellipse-shaped particles form little blobs throughout a drop of liquid. Some of them migrate to the edge, but not all. Not even most. If this were a drop of coffee on a table, you'd get a solidly brown round spot — no coffee ring.

The third part of the video gives you a closer look at the edge of a drop of liquid filled with ellipse-shaped particles. You can see the particles clump together and move away from the edge.

The fourth part is the close-up of spherical particles as they rapidly pile up on the edge of the drop, forming a ring.

In the final part, Yunker's team shows that it's possible to get the ellipsoid particles to form a ring at the edge of the drop. The key: Using a surfactant to decrease the surface tension between the particles and the liquid. Spherical particles move right to the outside edge because the attraction between particles is weak (relative to the elliptical particles). As liquid moves to the outside edge, it just pushes the spheres along with it. Normally, the elliptical particles are attracted to one another strongly enough that they don't get swept along with the current, so to speak. But the surfactant reduces that attraction and, like the spheres, they go slip sliding away.

Button is right that this particular paper doesn't offer much of an explanation for the shapes he sees in his Scotch glasses. They aren't all as circular as the the picture at the top of this post. Some look more like undulating hills and valleys, rather than coffee rings.

This paper of Yunker's certainly suggests that there's some interesting fluid mechanics at work here, though. I'm going to look into it and will report back on what I find.

Read Peter Yunker's full paper on the "coffee ring" effect

Check out Ernie Button's full series of Scotch glass photos, called Vanishing Spirits.