ещё одно маленькое уточнение относительно Asano Mikawa Shiro Nagura:
помимо 4-х видов нагура
(которые различаются по пласту (strata)
в котором они залегают и из которого их соответственно добывают):
Koma, Botan, Tenjyou, Mejiro
コマ ( 細 ) 、ボタン、天上 ( てんじょう ) 、目白 ( めじろ )
нагура также различается по качеству (grade)
резличают 4 градачии качества:
1) 特級上 Superior high grade
2) 特級 High grade
3) 別上 Superior selected grade
4) 上級 Superior grade
то, что не помечено из надписей --- это 純三河白名倉
то есть собственно название этой нагуры
The true Mikawa Shiro Nagura stone is mined from the 12 layers of the Miwamura mountain in the Aichi prefecture. The four famous and most usable strata are Botan, Tenjo, Mejiro, and Koma.
Koma: The finest particles; used for JP swords.
Mejiro: Very fine; prepares edge for final finishing stage; the best for razors
Tenjo: Intermediate grit; mean for light repairs; white ones are soft and fast while ones with layers (usually yellow) are hard and slow
Botan: coarsest and fastest; meant for major repairs
Dr. Kosuke Iwasaki, Mr. Shigeyoshi Iwaski's father, believed that you could use different nagura in different stages of the honing process on the same Nakayama stone. This would allow you to progress from a dull edge to a shave ready edge without the need for other stones. However, to gain the most out your J-nat, he believed that your final nagura wasn't a nagura at all but a tomonagura.
Tomo = same
Nagura = slurry stone
It means a slurry stone that is identical to your finishing stone. If your stone is a Nakayama Kiita, then you would use a small piece of a Nakayama Kiita as your tomonagura. If your stone is an Ozuku Asagi, then you would use a small piece of an Ozuku Asagi as your tomonagura. It doesn't have to be a piece broken off of your whetstone but it should have similar characteristics.
Since most of us don't have a smaller yet identical piece of our Japanese whetstones, then a diamond plate is recommended. The diamond plate works because it's harder than the whetstone. It will build a slurry made up entirely of particles from your finishing stone. Instead of the slurry of an 8K nagura, you're getting the slurry of a 20K+ whetstone. Those particles break down and get smaller and finer, which will refine your razor's edge far beyond the purported grit of the stone. Only experience will tell you how many times you must repeat the process of building and diluting the slurry.
The Mejiro nagura is softer than the whetstone. It will break down and create a slurry of its particles, which are much coarser than those of your whetstone. As those particles break down, they can help bridge the gap from your intermediate finishing whetstone (Coticule, Shapton 16K, Shapton Pro 12K/15K, etc.) to your final finishing whetstone (Nakayama, Ozuku, etc.). However, they will never be as fine as the particles of your whetstone or tomonagura. That means there's a level of edge refinement that you will never reach.