[mpierich]

You could try emery on sisal, but you'll probably have to start with 120 or 220-grit paper. On a big surface like that using wet paper would probably work well. I would probably use my (air-powered) jitterbug sander, but it could be done with any number of types of sanders or even by hand, if you have the elbow grease to spare.

Try 320 grit first then work backwards thru 220 then 120 til you find whatever works fast enough to suit you. After 320 or 400 you could probably go to emery (black) on a cotton wheel, then perhaps brown (tripoli) followed by white to color it up. Some people take the sanding way up thru 1000-grit but I usually don't find that necessary.