Paulus
Your right about the wheel. I took a opinal knife over to my mate "Frenchy" knife maker, to borrow his stones to sharpen the opinal. He looked at the edge, and just ran the blade along the polishing mop wheel a couple of times, and it was razor sharp again, No stones.
When used the edge curls over, and the wheel just straightened it out again. Try and take a fine slice off a ceramic "steel" would do the same.