One test for a counterfeit (U.S.) bill is to rub it on a piece of paper.
The ink on a genuine bill never dries, so you'll always get a slight
smear. Somehow that doesn't seem like a good thing to leave behind on a
relay contact you're trying to clean.

Roy Lewallen, W7EL

Richard Clark wrote:
. . .
You could also use a typing eraser to clean the mating surface. This
is an old board cleaning tip that was NASA approved back when there
were typewriters to need typing erasers. These erasers had the right
amount of abrasive without having too much. The same goes for a
dollar bill having just enough abrasive (useful for cleaning fouled
relay contacts). But none of this really takes care of the problem.
It simply puts you into the lock-step of a chemical dependency.
. . .