This coppa Nakayama I bought from Tomonori Nakaoka at 330mate by a direct request. I wanted to try a high quality Nakayama without having to sell my car. It was still quite expensive for a koppa, but the quality of this stone is excellent. It is not the most exeptional fine grit Nakayama, but it is very even grit with a totally clean and beautiful surface. If this stone had been a perfect rectagle 9" stone it would easily be a $1000++. That is the beauty of the koppa sized stones. You can score a very high quality grinding surface for a very resonable price.
The color of the stone ranges from a dull grey with orange brown nashiji spots through several shades of pink blue and orange to a deep greenish yellow. It is really an amazing palette this little rock shows up. To the right in the picture it even looks like a streak of Karasu appearing. That might be the reason this stone is so fast cutting and not as fine grit as I initially expected. The lines showing on the board are all solid and has no negative effect on sharpening.
Sharpening with this stone is fairly straight forward. It is hard but not exessively so, and as you can see from the below picture, it draws metal very quickly. The picture shows the black metal particles suspended in the still clear water after just 10 passes over the stone.
After about 50 more passes, the loose metal particles has drawn particles from the stone producing a dense and very fine slurry. The feeling of the grind with the slurry is very delicate and even. After another 50 passes the slurry had turned almost ink black (forgot to take picture).
The close-up of the Ji and Ha shows a scratch pattern that is coarser than what I was expecting from this stone, especially considering the delicate feeling and response from the stone during sharpening. I must say I was a bit surprised. It actually appears even coarser than the scratch pattern from the Ozuku Asagi. However the edge off this stone is significantly more refined and sharper than the edge off the Asagi, making this a very nice finisher for kitchen knives, probably in the #20-25000 range. The edges coming off this stone are also very wear resistant even with heavy use of the blade. Mirror finish sure can be pretty, but it rarely gives the best edges. You can find some very good reading about this theory here http://thejapanblade.com/sharpvsshiny.htm.
The slurry made with my diamond nagura is a yellowish beige drying up into a white to light yellow egg shell color.
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