This is the Nubatama Bamboo 15,000 grit stone, the finest stone in either of the Nubatama series of stones and the most recent stone developed for Nubatama. It is uniquely marked with 5 Kanji characters in addition to the Nubatama and Bamboo symbols both on the box and along the side of the stone (demonstrated). It is with great anticipation that I use this stone, having very high expectations for it (which were met or even exceeded).
It may be similar to the 2k and 3k Bamboo stones in style, but we will see. Porosity testing - This is a near splash and go stone, saturating fairly quickly. Not a very porous stone, holding its water quite well.
The first knife is a Masamoto fuguhiki - essentially a more delicate yanagi used for fugu fish preparation, but I find it fine for general use as a light yanagi. It is already a pretty good edge.
The stone is very smooth and quiet (love at first sight). Immediate ultrafine microscopic metal swarf formation occurs. A fairly hard stone, but it does build up a fine mud slurry. It is not as hard as a 30k Shapton but harder than a 12k Superstone. Absolutely perfect waterholding, allowing you to have consistent mud density and run the stone at high slurry concentrations. Very smooth extremely quiet stone.
Resultant finish shows a bright finish on the core steel (hagane) and a very uniform finish on the cladding, making this a superb final finish rivaling and in some instances exceeding many very high quality natural stones! In addition to knife sharpeners this is a stone many sword polishers should get very excited about too IMO. This is a stone that will last for a long time. This stone even though it is very fine gives EXCELLENT feedback - a silky feel yet a hard stone too.
I continue using the stone as much for the pleasure of using it. The result is an even brighter hagane with further surface refinement, nice contrast with the jigane.
On to the Nubatama Black steel paring knife. Black steel has easy sharpening ability and excellent edge retention too. I continue using the slurry from the fuguhiki, In an EXTREMELY short period of time I get immediate edge refinement / increased sharpness. The sharpened edge is a bright mirror. Effortless slice cutting and push cutting an inch out with just a quick touchup! This stone could be preceded with a 5k stone like the 5k Bamboo for natural stone finish preparation for an extremely fine natural stone or just left as is as a final exceptional finish. I would also expect that this stone would be superb for use with straight razors and kamisoris in particular. If you are so inclined, you could follow this with compounds such as quarter, eighth or tenth micron CBN and polycrystaline diamond finishes without losing the contrast to any appreciable degree.