"The Breadth of a Whisker" by Janet McNeill

  Each night the alchemist and the mouse meet in the lab to try to make gold. But after so many years, it is as much for friendship as it is for the gold. One night – almost absentmindedly – they succeed with just enough to coat the mouse's whisker but the Alchemist can't even remember how he did it, or perhaps simply doesn't want the nightly friendship to end.