As to the burnt cork that Morris Dancers use to paint their faces black:

Last year, I came upon the book "Santa Claus, Last of the Wild Men: Origins and Evolution of Saint Nicholas, Spanning 50,000 Years" by Phyllis Siefker.

She makes the claim that the practice of men painting their faces black goes back to ancient times, and is a ritual way for a shaman to impersonate the god of the wild, who was believed to tend the sacred fires, and therefore had a face continually covered with soot.

I also seem to recall learning from another source (which escapes me at the moment -- it was probably back twenty years or so), that in its earliest form, the ritual dance traditionally performed on May 1st started out as a representation of the battle between the forces of winter and the forces of summer. After the Crusades, this was changed to a battle between the Christians and the Moors, as is illustrated by the following lyrics from a May Day Carol (don't remember where it's from), "Hal-an-tow":

What happened to the Spaniards, To make them so great a boast-o? They shall eat the feathered goose, And we shall eat the roast-o!