In this video I introduce the 4000 grit Nubatama Ume waterstone. Like the Choceras, both the 4000 and 6000 grit Ume stones should not be soaked for long periods of time. As with any stone, care should be taken to not let them dry in direct sunlight or subject them to freezing temperatures.
First porosity is tested. This stone is a splash and go stone with a slow water absorption rate. The first knife used for testing is a Kikuichi TKC petty using a semistainless steel. The second knife, used in part two of this pair of videos uses a Hiromoto AS 300 mm sujihiki - a stainless clad knife with a carbon steel core (Aogami Super).
The Kikuichi knife is fairly dull, secondary to refinishing the sides of the knife that were scratched up.
The stone surface is exceptionally smooth. The stone is quite dense holding water on it's surface for a long period of time. I attempt to reestablish a bevel (successfully) using this 4k stone, something normally requiring a coarser grit. The stone is hard with no chance of gouging the stone with edge leading or trailing strokes - a very easy stone to use, generating a very fine metal swarf with little stone or mud content. The stone is also a very quiet stone.
A hard precise stone. Should also work well with woodworking tools and straight razors as well.
I finish sharpening the knife with a few edge trailing sweep strokes at a steeper angle to create a microbevel and get the two sides of the knife to meet without having previously created a burr. This combines putting a microbevel on an edge and getting the two sides to meet precisely within a couple of strokes, a technique that takes some practice to sense that "sudden increase in sharpness" that occurs right before generating a burr.
I briefly discuss the lack of necessity of generating burr on one side before switching sides as this burr would be off center of where the final edge would ultimately be.
So this is a splash and go stone - quite hard. Leaves a bright finish. A very precise stone generating little mud but quick enough to accomplish a task often reserved for coarser stones of defining a bevel / microbevel with ease.