"The Blackening is a fairly rough ceremony in which the groom-to-be is waylaid by his friends. He is stripped (winter and summer!), bound and "blackened" using a messy mixture that usually contains treacle, flour and feathers. The unfortunate groom is then paraded around on the back of a truck, while his comrades make as much noise as possible by blowing whistles, shouting, beating sticks, banging drums and generally creating a din with anything they can lay their hands on."

http://www.orkneyjar.com/tradition/weddings/blacken.htm