perma-dirt

A permanent state of dirty looking hands. A mixture of dirt and grease that stays on your hands no matter how many times, or how vigorously they are washed. Common for men in trades like automotive mechanic, heavy trucking, and welding. The hands will appear dirty and can be anywhere from slightly-dirty, to completely black

Wife: Are you going to wash your hands before we eat?
Husband: I already did, it's just perma-dirt