I miss recess. Also Recess. That theme really brings me back.

A recess is more than a great TV show from my childhood. It’s another word for a hidden gap. Recesses surround us, in bookcases and closets and cabinets. But recesses get much smaller than that, too. The proteins in our bodies fold into complicated shapes that no one understands even today, but we know enough to say the recesses in those structures are part of how proteins do their work.

Smaller still, surfaces are pitted and pocked all over the place on atomic and molecular scales. These bumps (and larger ones) are the source of friction, as we saw a couple posts ago. But let’s zoom out from that scale to a paper towel. We find recesses there, too. If you take a maker and make a dot on a paper towel, you’ll see the dot expand even after you take the marker away. This happens as ink flows in and out of recess between the fibers of the paper towel, pulled along those fibers by capillary action: Each molecule gets pulled forward by the fiber a little in front of it and pulls the molecules behind it along, too. (That’s loosely stated, but we can’t do everything all the time.)

Capillary action is why notes written in pen on paper towels start out neat and end up looking like ransom notes. Paper towels are made to be particularly good at pulling liquid along the fibers. That way, the part that’s actually touching the source of the liquid can keep sucking up more instead of saturating, and the paper towel cleans up whatever spilled. Paper, though, is made a little differently. Its fibers don’t shuttle liquid around quite as much and ink generally sits more on top than soaking in. But ink still bleeds a bit, even with the best of papers. If you don’t want closed es and gloomy qs, write in pencil on stationery.

Of course, pencil smudges. But that’s neither here nor there. (If anything, it’s both.)