A mixed grit 'muddy' stone graded at 2000 grit.
The man-made aoto stone starts cutting at 2,000 grit and easily removes scratches from anything 800 grit and up, but if the slurry is left on the stone and forms a thicker mud. This thicker mud when left atop the stone provides a much finer finish and starts a mirror polish, somewhere around 4,000 grit. A shop favorite for single bevel knives, aoto stone is extremely useful in preparing and polishing wide bevels by doing both jobs of 2,000 and 4,000 stones. The left over mud generated when mopped up onto a cloth makes a great rust remover.