Shigefusa 270mm kasumi yanagiba with custom, by me, desert ironwood handle

30 Nov 2010

Twice as nice - Yamashiro karasu 180x65x18mm #6-8000 + #15-20000

This is another stone I bought at a dutch auction from When I got the stone I was amazed over the clean board and very nice colors. It was basically a kiita coloured stone with pink and green shades, but more visible was the very nice karasu breaking through. My first sharpening session, however, was a mixed experience.

The response from the stone was beautiful. Very efficient as the karasu in the stone pulled metal filings from the first pass and in addition it did not take more than 25-30 passes before I had built a nice thick creamy slurry. The down side being that the underside of the stone was not level, making the stone rock around.

I took the stone to my workshop to try to chisel of the unevenness by removing the rest of a layer that was about to part from the stone anyways. After this large flat chip was removed, I discovered a beautiful, dense and dark silvery grey karasu board underneith. I threw all sensibility overboard and with my coarse diamond plate, I ground away the rest of the very nice skin on the underside of the stone revealing a full board of dense, uniform karasu. I was just staring in awe for a moment at that absolutely beautiful karasu appearing from under the skin.  

As the karasu was so dense and dark, I expected it to be quite scratchy and coarse, so I took one of my lesser knives to test it out. I did not at all expect what happened next. The darker side was significantly coarser than the top "kiita" side of the stone, as I suspected, but it was not at all scratchy. Not one bit! It felt a little bit like a very nice and uniform Asagi only even more aggressive. In the back of my head I could almost hear Darth Vader thunder "Come over to the dark side, Darkhoek. Feel the force!" :o)

As you can see from the pictures, there are some white lines on the dark side. These lines are softer than the rest, probably contributing positively to the very nice slurry building on the dark side as well. The lighter shades mixed in with the carasu I suspected to be trases of skin or rust at first, but it is actually the kiita side breaking through to the dark side, helping to refine the slurry and making this stone a perfect blend.

The dark side pulls metal from the first pass with just water on the board. No wonder, considering the density of the mica making out the karasu. However, the stone gives up a very nice, dense slurry after only a few passes, making it very enjoyable and delicate to use, and as I mentioned earlier, totally free from renegade scratchy particles. After some work, the particles seem to break down to a very fine grit, making the slurry almost as fine as the slurry of the top side.

Judging from the scratch pattern I would grade the dark side of the stone very close to my Ozuku Asagi at #6-8000 grit, and as you can see the scratch pattern is very uniform and fine with few visible lines. This patteren is achieved using the slurry, which shows a pattern a lot finer than the #6-8000 and closer to the top side comparing the scratch patterns from both sides of the stone. Sample is 20mm across.

The lighter side is more of a finisher. It is exeptionally uniform and clean, and the karasu makes for a very efficient stone. The light side also gives up a dense creamy slurry quite quickly, even more slick and delicate than the dark side.

Scratch pattern shows a very uniform and fine grit perfect for most kitchen knives exept the most demanding sashimi slicers, which requires my finest Ohira suita or Nakayama. You can see the difference mainly in the lamination line between the Ji and Ha, where the top side shows almost no scratch marks at all. Apart from that the two sides are a lot alike using the slurry effectively. Sample is 20mm across.

The reflection pattern shows an apparently highly polished edge with a clear contrast between Ji and Ha. This polished look is actually due to the very fine scratch pattern from the natural stone. Looking at the picture above the surface is actually matte to the look. This highly complex scratch pattern I believe is one of the main factors to get the edge really sharp and more wear resistant than an edge polished to a full mirror finish by fine synthetic abrasives. You can find some very good reading about this theory here

Seen from the side, the stone shows a very even transition from the light board on top to the full dense karasu side on the bottom. This will probably result in the top side gradually showing more karasu over time and the dark side to gradually lighten up until there is no more stone left. As I intend to use this stone carefully and wisely, I am sure it will give me many years of enjoyment. 

Summing up, I can't really believe my luck with this stone. It is really two very good stones in one, and a perfect stone to carry for travel, as it can erase micro chips easily with the dark side, and refine the edge to a razor sharp using the light side. I have not really seen anything like this stone before, and I could only whish it was full size, but then I could probably never afford it. Darth Vaders words to his son Luke have never been more true: "The force of the Dark side is strong, Luke!"

25 Nov 2010

Aizu vs Aoto - Medium finishing stones #1500-5000

In this post I will try to make a comparison between two of my main medium sharpening stones. I have chosen to do them together as they actually are more similar than different, even if this is not immediately apparent. One is the very well known Aoto, which I got from Tomohito Iida at Iida Tools, and the other is the less known Aizu, which was brought to my attention and delivered by Maxim at Japanesenaturalstones. Both are very substantial stones; the Aoto measuring 240x95x95mm and weighing in at almost 9 pounds and the Aizu measuring 210x80x67 weighing in at about 5,5 pounds.

Both stones are also quite rare, but for different reasons. The Aizu because the mining ceased in the 1950's and have not been mined since, the Aoto because of the massive size and the exeptional quality and grinding force which is very rare to find in an Aoto these days. Especially outside of Japan. To put it simple, this should be very close to "as good as it gets" regarding medium grit Japanese natural sharpening stones.

Looking at them side by side, they could not really be much more different from each other. The Aoto is a dark blueish to charcoal grey with what looks like olive green sesame seeds embedded in the grey. The Aizu is a solid chalky white with almost translucent olive green lotus or renge embedded in the white base. The Aoto has a beautiful skin on both sides while the Aizu is sawn with a large, coarse circular saw leaving a beautiful almost sculptural surface on five sides. I think they are both really visually stunning in their own way. 

In the left picture below you can see the white board with translucent olive green renge spots of the Aizu stone and on the right, the dark grey board also with olive green spots on the Aoto. Actually I was a little bit surprised to find the spots with almost exactly the same color in these two stones. I am not sure that the olive spots are the same material in both stones, though... 

Except for the obvious differences in appearance between these two stones, the biggest difference is noted immediately when starting to sharpen on them. Initially, starting out with a clean wet surface, the two stones feel very similar in grit size. A bit like a #1200-1500 man-made stone. However, I could almost immediately feel that the Aizu was a harder stone than the Aoto, requiring a lot more work to build a slurry. Both of the below pictures show the slurry produced after about 50 passes on each stone. The Aizu to the left, still with the surface of the stone as the main grinding factor, and the Aoto to the right, already with a dense slurry smoothing the feel of the stone.

This difference makes the Aizu a more aggressive stone by working the stone surface for a longer period of time before the slurry develops to a buffer or lubricant for the sharpening process. A very good thing about the Aizu being significantly harder is that I feel a lot more confident when sharpening chisels or kanna blades with very narrow blade roads, which can easily dig in to the softer surface of the Aoto. The Aizu is a lot more resistant to this "digging" thus a lot more forgiving to my lack of experience in sharpening these kinds of blade. Aizu is therefore my preferred medium sharpening stone for blades with narrow and flat bladeroads like kanna blades and chisels. For knives, the Aoto gives me the better feel and a more velvety response during sharpening.

So, lets take a look at the final results. After about 100 passes on each stone, both stones had built a slurry dense enough to effectively buffer the stone surface from the steel. I did about 50 more passes with full slurry before comparing the results. Samples below are 20mm across. You can see the scratch pattern of the Aizu to the left is a little bit more pronounced showing a few more clearly visible scratches than the sample from the Aoto to the right. The explanation for this might be that even after the slurry was fully developed the Aizu felt a little more "grindy" compared to the very creamy Aoto. Probably because the Aoto particles break down even more than the Aizu particles. The scratch pattern from both stones was just about equally easily erased by the Oohira Asagi reviewed in one of my previous posts. These stones can actually be used as finishers for most stainless and daily use knives. An edge off either of these stones will easily beat the main stream factory edge and making the edge a lot more wear resistant.

It is very hard, if not impossible, to decide a winner between these two magnificent stones. Both stones have unique qualities making them highly useful and desirable. The hardness of the Aizu is great with kanna blades and chisels and the softness of the Aoto is great with most knives. The difference in grit size and sharpening result is marginal between the two, the main difference being the difference in hardness of the surface.

If you only sharpen kasumi or stainless knives, I would probably go for the Aoto. If you sharpen both knives and chisels or kanna equally often, you will need both. If I have to choose, I would probably go for the harder Aizu, due to my lacking sharpening skills on kanna blades and chisels. If you only sharpen kanna or chisels I would be very happy to live with just the Aizu. Fortunately I am the very happy owner of both.

Maxim at Japanesenaturalstones tells me that the Aizu also is a lot more effective than the Aoto on Honyaki blades. Truth said, I am actually quite happy with my Aoto's effect on my Honyaki knives, and so far I have not had the time to test the Aizu with my Honyaki. However, I have no reason at all to question Maxim's experience on this. He is a trained professional with significant skills and knowledge on japanese natural stones and the application of them on different kinds of steel. If you are interested in further reading on the Aizu, Maxim also has a very good description on his web page (se link on the left menu).

21 Nov 2010

Nakayama? 200x90x30mm #10-40000???

This stone is a true mystery to me. Everything I thought I knew about judging the quality of a natural stone came short here. It is large, brute and ugly with a lot of cracks and lines. It is very oddly shaped in a near perfect parallellogram, askew the wrong way to my sharpening angle. Still I love this stone to bits, but why?!

I bought this stone in a batch of very low priced stones from I paid about a $100 for 6 very different coppa stones planning to use them for Nagura or Uchigumori stones. When I opened the wrapping on this stone I was at first surprised by its large size, but after a small inspection I understood why it was priced so low. The board was full of small hard inclusions, cracks with skin inside which would really mess up my blades, and absolutely packed with lines over the whole board. It looked like crap!

I was about to throw it in the bin at once because I did not believe this could be used for anything or be saved by lapping the surface down. However, before throwing it away, I wanted to feel the grit of the stone and the hardness of the inclusions to see if it could be used as Nagura or maybe Uchigumori stones, so I started lapping it anyway. After just a few minutes grinding away with my #140 grit diamond plate under running water, something started to happen. Fast!

I obviously finished out a dirty layer of the stone. The deepest crack closed in and a lot of the small hard inclusions disappeared with it. I kept on lapping on a new layer. More lines disappeared and the color of the stone changed significantly showing a very strange mixture of colors in one single stone. One side looking and feeling like the red shallow stratum Aka-pin, the centre looking and feeling like a fine Asagi and the other side looking and feeling like a medium hard honsuita. I have never seen anything like it. Three very characteristic stratum in one single stone? There are still some lines and cracks left, but a close inspection and test have shown that they will not scratch.

The typical orange skin often seen on Nakayama stones. Not very pretty, though.

The stone is a multitude of grits and hardnesses. However, it seems like a fairly soft stone overall but with an amazingly fine grit compared to the average hardness. The picture below shows a dense creamy slurry forming after just 30 passes on the stone. The feeling is very delicate, totally without scratcy particles in the slurry. I can hardly believe this stone.

This close up shows an amazingly fine scratch pattern with an almost pefect mist and haze on both Ji and Ha. The slurry of this stone must break down to an extremely fine grit. Compared to my other fine stones I would suggest this to be in the #40000 range, but that's the slurry talking.

Another exeptional feature of this stone is the contrast it makes between Ji and Ha. I have never seen a better contrast from a natural stone. A highly polished edge in contrast to an almost non-reflective blade road. It is really amazing!

The reflective test shows to what high degree this stone polishes. This polished look is actually due to a very fine scratch pattern from the natural stone. Looking at the close up picture above, the surface is actually matte or hazy to the look. This highly complex scratch pattern I believe is one of the main factors to get the edge really sharp and more wear resistant than an edge polished to a full mirror finish by fine synthetic abrasives. You can find some quite interesting reading about this theory here:
This stone is remarkable! This stone must be the bargain of the century. It is still brute and ugly, full of lines and cracks, but it is really an amazing stone that has thought me to think differently about the looks of a natural stone compared to its qualities.So, what have I learned from this stone? Not to judge by the looks, always give the stone no matter how ugly at least one chance to show itself and finally that treasures can be found in the scraps. Happy hunting!

Nakayama honsuita 180x65x35 (koppa) #30-40000

This stone I bought from an auction at I have gotten a lot of stones from them in wholesale batches at very low prices. Some stones have been really bad and some merely mediocre, but a few have become good and even excellent stones after a bit of work with my trusty #140 diamond plate grinding trough the dirty layers on the search for a clean board. A couple of the stones I have gotten from 330mate have been real bargains. Some of the better stones are sold at their Dutch auction, but you can take even more of the uncertainty out of the equation by requesting a specific stone from them, as I did with the 130x85x33mm Nakayama koppa, but then you will have to fork up a lot more money for their efforts selecting a good quality stone for you. That said, I kind of enjoy buying batches of low priced ugly looking stones from 330mate, searching for that one jewel to be found. It has happened to me a couple of times, and it is a very exciting feeling when it happens.

This stone was actually very good straight out of the box. Well lapped, clean board and ready to go. The board shows a lot of the same colors as the previously mentioned Nakayama, with green, yellow and pink shades entwining on the board almost like waves on this one. It is a little bit narrow but has good thickness and it looks fairly uniform through the stone making it last at least my lifetime and then some.

You can see a few lines and cracks on the board, but none of them affect sharpening. The grit from the red area seems to be a bit more agressive, and pulling slurry with a diamond nagura from that area greatly enhances the speed of the stone. A little turbo grit :o) Very practical. Every stone should have one.

 The skin showing on the side needs to be ground down from the board as it is very hard.

The stone is very efficient even without using a nagura making slurry. In the below picture you can see a lot of metal filings floating in still clear water after just 10 (top) and 20 (bottom) passes over the stone. That is just amazing!

After 50 passes the stone has given up a light and extremely fine slurry making the sharpening more smooth and leaving a very fine scratch pattern and good polish. 

As you can see from this close up, the scratch pattern from the stone is very fine and homogenous. However it makes only a slight contrast between the Ji and Ha. This shows that the stone polishes both Hagane and Jigane equally well.

From the reflection picture, you can easily see the exeptionally fine finish this stone puts on the knife. This polished look is actually due to a very fine and complex scratch pattern from the natural stone. Looking at the close up picture above, the surface is actually matte or hazy to the look. This highly complex scratch pattern I believe is one of the main factors to get the edge really sharp and more wear resistant than an edge polished to a full mirror finish by fine synthetic abrasives. You can find some very good reading about this theory here can easily shave with any high carbon steel edge coming off this stone.

This stone is one of the best bargains I have made from 330mate. A really amazing stone at a very, very reasonable price.

Nakayama Nashiji Kiita 130x85x33mm (coppa) #20-25000

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

The slurry made with my diamond nagura is a yellowish beige drying up into a white to light yellow egg shell color.

Oohira Asagi 207x75x25mm #6-8000

This is a stone I was recommended from Iida Tools as a pre polisher to use inbetween my Aoto or Aizu stone and my final polishers. The stone is very dense weighing in at 1.75kg or almost 4 lbs without the base, which is quite heavy for this size of stone. The stone is covered in a beautiful dark golden brown cashew laquer on 5 sides for protection. As with my other stones I have mounted it on a wooden base to make things easier and more efficient when I am sharpening. The base also stabilizes the stone on my work bench, making my sharpening a lot more consistent over time.

At first eyesight the Asagi looks a bit dull and gray in color, much like the close up picture below, but if you wet it down, a beautiful deep green and blue color with yellow tones appear. It's almost like looking down into a deep ocean on a sunny day. Fascinating!

The Oohira Asagi is a fairly hard stone, but pulls black metal particles very fast and gives up a very fine slurry after a short while, even without using a nagura. The picture below shows slurry after about 50 passes over the stone starting out with just water.

The grinding feel is really good with this stone. At the beginning and without slurry you can easily feel the grind of the stone but as soon as the slurry builds up the grinding is a pure pleasure. I have read descriptions by other Asagi owners on the web describing the feeling of a good Asagi almost buttery, and that is no exaggeration. The feeling is really smooth, almost like dragging the knife edge over oiled velvet.
When using a diamond nagura on a clean wet stone, a yellow/green slurry is produced. The slurry dries in to a light yellow/beige powder, which is a bit of a surprise considering the dark color of the stone itself.

So, what about the final result? As you can see from the pictures below, the scratch pattern on the blade road is very even, making a very nice contrast between Ji and Ha and producing a very nice mist and haze. It is obviously not a final finisher for the most demanding blades, but an edge off this stone is very wear resistant and has a very good "bite" to it making the knife very useful and efficient on most foods. A very good touch up stone i a demanding kitchen.

This sample is 20mm wide. It shows how nice this stone really is. The edge is very refined and for most of my kitchen knives this edge is actually more than good enough. This close-up also shows the excellent quality in the lamination between the two steels in my Usuba knife, also from Iida Tools.