I have a new Arkansas stone that came in a box entitled the cutters edge. I wouldn't have gotten it but i i got it with another stone for 15 dollars. The Arkansas stone is a little of 12 inches long and is semi worn. How can i refinish or make sure this stone is flat? i was thinking about taping some 220 grit paper to my granite counter top and use that against the stone. Is that the right grit for sandpaper or should it be higher?