Sigma Power Corporation in Tokyo has specially developed these premium stones for sharpening harder steels, such as VG10 and SG2. In addition, they are of course also suitable for the softer steels. Sigma has ensured that these stones offer a sharpening experience that is comparable to that of natural stones. The advice for use is to put the stone in water for 5 minutes the first time. When using next time, only wet the surface of the stone.