Chef K.C. Ma (a professional chef who has worked in some of the top restaurants in North America) had this to say about the Naniwa, and the 5000 stone in particular:
"This is my favorite polishing stone :) it does amazing things. I think it's great that you carry it, and I think your customers [...] will really appreciate this. As for maximizing the Naniwa Super Stones at 3k+ for final sharpening/polishing, my trick is to soak the stone a bit, it works without soaking, but i think all polishing stones benefit and sharpen better when slightly soaked. I rinse mine wet, and then cover it with wet paper towel until I'm ready. The Super Stone, like natural stones and some other finishing stones has a range, not just a fixed grit. While the abrasive is uniform, its behavior changes. After soaking, I will flatten the surface with a small diamond plate (8k), then i sharpen on the mud from the stone. As I sharpen, the stone dries up a bit, the intuition is to splash more water and rinse off the mud; don't. Keep working the mud until it's almost 'pastey', at this point the stone will take on a property finer than the grit rating given to it. 5k stone easily polishes to 6-7k range, and 10k stone poishes to 12k+ range. Sharpen until it's almost dry, then add just enough water, a splash or 2 to get it moving again. These stones are especially appreciated on katsumi style [damascus] knives. Without using the mud to push its ability, most stones will give you even polish, blurring the 2 different steels. But Naniwa is a very easy stone to use in that regard: its mud is easy to work with, and when used carefully, it creates the most distinctive layer of 2 steels on katsumi [damascus] knives of all synthetic polishing stones and gives my knives the best edge."