These are natural Japanese Honyama stones. They are waterstones that are harder than belgians and require a chalk nagura to start a slurry. The grade B stones are pretty rough and by that I mean you'll get one good side and that may be uneven in hardness i.e. soft in some areas and hard in others. I keep one in my collection but don't use them for razors anymore as they're too hard. I like the softness of the coticule and it works well to produce a shave ready edge.