Which means we were using crucibles.
Long story short, I accidentally bumped my right thumb into the crucible lid when it was fresh from the Bunsen burner. Now the crazy callus build up I had on my thumb cooked and burnt onto the lid. So now the lid has this really cool, smooth and glossy black splotch was was my skin.
Coolest thing that's happened to me all day. You can even see my finger print.