Jeremy Osner

I've managed to get this gouge just about sharp using a few different slipstones on the inside of the blade. But the "flatness" of the back is only for a couple of millimeters above the sharp edge. What would be the best way to clean up the rust beyond where it's sharpened? The blade is curved in two directions so no stone will really work. Except maybe the end corner of a rounded slipstone?