I sharpen my own knives, soft steel Japanese carbon steel. I use three stones, the left stone is a very coarse stone, the middle is very soft, natural stone, and the third is the stone I use to keep my stones flat and even.
These stones are basically judged by their coarseness – Japanese water stones are both natural and synthetic, known for their quick-working qualities for Japanese tools. The small particles that do the cutting are loosely bound together in the stone, and so during sharpening, the surface particles are quickly washed out, allowing new, sharp, particles to start working on the blade. These water stones must be lubricated only with water.