I believe one way is to scour it with steel wool then cover with dark shoe polish and wipe off the polish immediately. This will leave dark scarring.

Depends on what color you want in the final outcome. The above sounds good. I took a white cabinet door and dry-brushed it using a medium shade of grey. It was super easy and looks wonderful! Then I painted a black cat on it and hung it over the old breaker panel on the kitchen wall. Ta-da!