+1 for the diamond polishing pads. The right grit for stoneware is between 150 to 250 grit. They cost $10 to $15 each, but you only need one, and it will last about 20 years.
just google "diamond polishing pad" and you find places that sell these hand held pads made for stonework. You can get different grits. The very fine grit will put a smooth finish on your bottoms with just a few swipes.
Edit: google "diamond HAND polishing pad" and you'll find the block style of polishing pad, as opposed to discs and sheets.