What does Rudy rub all over his body to imitate Jesse Owens?

Rudy covers his body with coal dust to imitate Jesse Owens.

On Himmel Street, he was considered a little crazy. This was on account of an event that was rarely spoken about but widely regarded as “The Jesse Owens Incident,” in which he painted himself charcoal black and ran the 100 meters at the local playing field one night.