I Hate the Whiteboards in the Math Building

I teach my honors gen-ed class at about 10am, so the whiteboard in the room was already nasty from two classes' worth of use. I was too lazy to hook up my laptop and use the SmartBoard, so I picked up a marker and started talking about how the cardinality of the set of natural numbers compares to the cardinality of the set of rational numbers.

Eventually we reach a point where the board can not be cleaned by further erasing. A nasty haze of grey covers the board with a plasticy film. It's like the coal soot that coats the inside of the walls of my house. Black, persistent, and particulate.

Tentatively, I start to clean the board with the board cleaner. All it does is to dissolve the marker grit already coating the board into a liquid grey film that then starts to evenly coat the entire surface. It's worse than before. I start debating with the class what the best board cleaner would be. I put in a vote for cheap vodka (alcohol to dissolve the marker, water to carry away the crud) together with a soft towel. They suggest that I should bring vodka to class. I remind them that we have a dry campus.

The stain lingers on that part of the board. Now that section of the board is even less useful. Our tangential discussion that real numbers do not have unique decimal expansions is crowded into a narrow sliver next to this stain. Cantor's diagonal argument awkardly skips over the stained part of the board.

Can this mark be erased? No, the erasers are full of marker crud, and when they encounter the film, its solvent nature pulls all of the pigment out of them and spreads it on the board.

Eventually one of my students volunteers today's issue of the student newspaper. Crumpled into a wad, the newspaper vanquishes the spot on the board. The entire board is the color of smog, and the next class will have to try to muddle though the haze to read what's written on it.