Atago Medium Quality. This stone is a middle grit natural in the 2K grit range. The stone can be used as a single sharpening stone for most knives and leaves a nice toothy edge. It weighs 3 pounds 13 ounces so it's big and measures 8" x 3." x 2". It also makes a perfect pair with the Ohira Tomae finishing stone.
Here is some information from my supplier, Mr. Imanishi on the stone.
Atago stone, we have mined about 30 years from 50 years ago. Stone layer is thick and the quality is stable.
It is easy to use just hardness. It is a fine stone to represent the district Tamba.
I think that quality is equivalent to that district next best Ohira. Because of the thick stone, it is painted transparently on the side of the stone in order to prevent cracking.