Since they started to produce knives out of steel, sharpening has always been done on stones. In the tradition, Japanese knives were sharpened using natural stones carefully selected from Kyoto area for the excellent quality. This stones were categorised in three main groups: arato, nakato and shiageto, respectively rough, medium and fine grit.
Nowadays stone are available in many other shape and quality, but we can still divide them in two main groups: Natural stones, and Sintetic stones.
Coarse grain. These grits are perfect to set a new sharpening angle or for repair quickly a chipped blade.
Medium Grit. The stones with medium grain are the right range to begin to create the edge of your blade before moving to fine stones.
Fine Grain. These fine-grained stones are just what you need to start having razor sharpening effect.
Super fine grains. If you are not satisfied enough with your sharpening, with these stones you will be able to polish your edge to a mirror effect, that will give you dizzying sensations on the cutting.