Beautiful nashiji and namazu Nakayama from a shallow tenjyou layer making it perfect for final finishing of bi-metal laminated blades. A great cutting stone, and so fine that yesterday I honed 4 razors with it and each razor shaved equally well (Gold Dollar 66, Henckels Friodur, a vintage Henckels #16 carbon blade and a Wade & Butcher Celebrated Hollow Ground). The W & B is a fickle steel to hone. Each steel was cut without coaxing, fast and fine but be  cause of the size I am recommending this as "the best knife stone" you could ever own. The black just peels off this Masamune blue steel deba with clear water only.
An expenisve stone, it does a maridian layer flaw running around the sides and ends.  A mystery inclusion, it is solid at this point, and will be reached at that depth maybe 5 years down the road.
A highly recommended elegant stone with a kiita base color leading to a more intense tomago kiita namazu pattern. Will come with a tested tomonagura appropiately sized for the stone.
 
Hardness 4
Fineness 5+
Speed 5++