I remember reading at some crazy scientists website if you smear mercury on aluminium it interferes with the oxide coating and the Al just oxidises away.
I tried it just now in my lab and the mercury can not be smeared, it forms balls and rolls away, no interfering of oxidising occured on the aluminium surface. I thought maybe the mercury is coating in oil of some type and washed it in solvent, still nothing. I tried sanding the aluminium surface and then putting mercury on it. still nothing !
The crazy scientists website said americans would try and smear mercury onto aircraft of the nazis. Well I sure as hell don't know how they could have, and come to think of it the aircraft would have been painted anways.