Japanese Nagura Stone.

For use with the finer Japanese waterstones, this  Traditional 'Nagura stone' can be used to create a slurry on the surface that aids the sharpening process, to create a razor edge.

Submerge the stone (as with the waterstones) before use and then move over the surface of the waterstone in a circular motion to create the slurry, then sharpen as normal.

Made in Japan