I begin reviewing the 5000 grit Nubatama Bamboo stone by testing stone porosity. Dry, the stone feels much like the 4k and 6k stones. I added the 5k stone to give users a more complete selection of stones.
The stone absorbs water slowly, making it a splash and go stone. Very convenient.
The first knife to be tested is a Blazen 270 mm sujihiki, using a powdered steel.
Next is a carbon steel (probably white steel) nakiri - a very thin blade. Unknown maker. It is easy to see the hand forged hammering marks across the entire knife including the hammering just below the edge.
Next is a Tojiro bread knife. I will demonstrate how to sharpen a serrated edge with a waterstone.
I begin 'touching up the Blazen. The stone is a hard stone. It is hard like a 5k Shapton, but with more feedback. There is no danger of cutting into the stone because of its hardness. It is MUCH harder than say a 5k Chocera . We do get a fine metal swarf pretty quickly. The finish produced is shiny / mirror. Very slow water absorption. It is also comparable to the hard to extra hard Nubatama Ume 1k speckled stones in terms of stone hardness. Unlike the Shaptons, you do get some mud buildup giving a denser slurry. The metal swarf component of the slurry is microscopic in size. I continue sharpening as the edge becomes increasingly sharp. The stone seems quite flat out of the box. I emphasize the advantage of developing an ability to test sharpness especially as one approaches the development of a burr. The resultant edge is a mirror finish. Slice cutting performance is excellent, with push cuts ~ 1.5 inches out. Excellent stone for [this] powdered steel.
Now the carbon steel nakiri. A zero grind edge. Continuing with the mud from the previous sharpening. The feel is much like a Chocera 5k but harder. I test for contrast, not necessarily expecting it - but hoping. Low water absorption - much like a natural poishing stone. AH - I AM SEEING CONTRAST. Getting some burr formation. As expected, the stone 'cuts' or abrades carbon steel faster than powdered stainless steel. Given the contrast this stone may be an excellent followup past the 3k bamboo if you wish to maintain contrast. Effortless slice cuts with ~ 2 inch out push cuts. THe hagane or core steel is a mirror finish with some slight haze, much like the kurobakari finish seen with natural stones.
On to the Tojiro bread knife. I demonstrate how to sharpen a bread knife by determining the angle required to sharpen and then tilting the knife to just be touching the edge of the stone. This is best seen rather than described. I follow this with a deburring stroke on the side opposite the serrations just close to a flat grind against the back of the knife. Results are excellent slice cutting and push cutting if you push in an individual serration.
Overall impression - excellent touchup stone. Works well on stainless and powdered steel knives and even better on carbon steel knives where it develops and maintains contrast between the soft cladding and the core steel or hagane.
I wasn't expecting this contrasting ability so this comes as a most pleasant surprise with this stone!