I think the best place to start is the 'ol vinegar and steel wool method. 
Below is a video that might help:
taking a look at this 'Instructable' might also prove valuable. There are many other variations on this theme and method out there, too.
Best of luck, and happy haunting!
Below is a video that might help:
taking a look at this 'Instructable' might also prove valuable. There are many other variations on this theme and method out there, too.
Best of luck, and happy haunting!