Jnat experts wanted: what do I have?

I bought this hone about 15 years ago from a woodworking store. It was sold to me as a very fine finishing stone. The box has no markings other than “Karasu 10”. I know that Karasu means crow in Japanese and refers to the pattern, not the type of stone as far as I know.

Does anyone know what it might be?

As far as the stone is concerned, it is very hard, and it takes a long time to raise a slurry with Nagura. Some razors seem to respond well to being finished on it, but others less so. Even after all these years, i am still figuring this stone out. Perhaps I need the right tomo nagura for it?

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Can you post a good image of the ‘skin’ on the bottom edge in the first image?

On those hard stones a 1200 Atoma or equivalent DMT to creat a slurry is a great way to start after you set the bevel. Then finish with your tomo.
Great looking stone by the way!

Here is the skin, only visible on one side:

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The skin is not on the bottom of the stone? Nly the sides?

No expert here. Anyway looks like both sides may be usable. Carpenter shop may indicate it is a tool stone but no way to find out till you find out. This is how i test stones, not the only way or best way its just what i do. Take a razor and do a slew of half strokes on it. Then i take wipe it with a white paper towel and see if it self slurries. The stone color is what you would see. Then I would take a razor and look at the scratch patterns to see how course they appear, water only, then with slight slurry from a diamond plate. Some karasu are scratchy. Finish a razor to 12k or so with a synthetic stone and then see what that stone does to that edge in a shave test. I would use a diamond plate generated slurry about the size of a quarter and see. Do that and test shave it.

That’s right! The two sides are pictured in my first post.

Well, the skin didn’t help much, but it was worth a tey. There aren’t any sparkly black patches on the skin are there?

Judging by the color and hardness, it may well be from the Ozuku mine (just a wild guess). It's a finishing stone - that's all that matters. Looks good to me in terms of the surface - nice and clean.
Hope you can unlock its secrets!

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Originally Posted by Steve56

Well, the skin didn’t help much, but it was worth a tey. There aren’t any sparkly black patches on the skin are there?

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No sparkly black patches, no.

I just gave this stone a good try again, as it has been on my mind. I dulled the edge of my old beat up Henkotsu kamisori on a glass, and took it to this stone. I used slurry from a Tenjou and Mejiro nagura consecutively, thinning the slurries as I went along. Then I stropped it 30 laps on linen, gave it 10 laps each on balsa with 0.5 and 0.25 micron diamond paste. Then 10 more laps on linen, and 40 laps on leather. Result: a really keen edge - I wonder if with the stone's own slurry, or a suitable tomo nagura, I'd be able to leave out the pasted balsa strops altogether.

IMO, You now have a Diamond paste edge. It's no longer a Jnat edge. But you know what they say about opinions. LOL.

Take the edge up to 8k synthetic, Then use a Diamond card on your stone to raise slurry. This will make it the stones only slurry. From there finish on it. That will give ya a better idea of the stone. Not all the Naguras. I'm nowhere near a pro honer or a Jnat pro, but I manage to get keen edges on Jnats! Good luck.

Yup. If you want to learn the potential of your stone, finish it on a diamond slurry, you may want to experiment with this stone with a western razor.

Set the bevel with a 1k then diamond slurry and dilute to finish, you will learn a lot about your stone, slurry making and performance. And if your stone is a finisher.

Save the diamonds for touch up or if you need a little punch up, but only a few laps.

A chrome oxide strop will calm most edges, you don’t need much or many laps. There is no benefit to killing the edge on glass, just hone it. Once it is on the stone, the old edge is gone.

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Originally Posted by Gasman

IMO, You now have a Diamond paste edge. It's no longer a Jnat edge. But you know what they say about opinions. LOL.

Take the edge up to 8k synthetic, Then use a Diamond card on your stone to raise slurry. This will make it the stones only slurry. From there finish on it. That will give ya a better idea of the stone. Not all the Naguras. I'm nowhere near a pro honer or a Jnat pro, but I manage to get keen edges on Jnats! Good luck.

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Originally Posted by Euclid440

Yup. If you want to learn the potential of your stone, finish it on a diamond slurry, you may want to experiment with this stone with a western razor.

Set the bevel with a 1k then diamond slurry and dilute to finish, you will learn a lot about your stone, slurry making and performance. And if your stone is a finisher.

Save the diamonds for touch up or if you need a little punch up, but only a few laps.

A chrome oxide strop will calm most edges, you don’t need much or many laps. There is no benefit to killing the edge on glass, just hone it. Once it is on the stone, the old edge is gone.

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Those are really useful insights. I don't have a diamond plate but perhaps it is time to invest in an Atoma, which would be useful both for lapping and for generating tomo slurry. I don't have an 8k synthetic, only one other Jnat (very soft and of polishing grit) and a Naniwa 1k/3k combination.

I found a stone that looks quite a bit like mine, and is also very hard:

https://www.japanesenaturalstones.co...su-lv-5-a1871/

Who knows! Some more experimenting to do. I really appreciate everyone weighing in and giving tips, thanks everybody!

It is difficult to positively identify a stone from a photo, except for possible some stone dealers who are more familiar with stones and have handled hundred or thousands of them. Even then stones from the same mine, quarried at the same time, by the same folks can vary, natural stones can vary from one side to the other. Really what matter is the performance of your stone.

A diamond plate will keep your stones flat and can be used to make slurry. Finer plates make finer slurry, but it does not matter that much as Jnat slurry breaks down.

If you are going from a 1 or 3k edge you want some aggression to refine the stria and straighten the edge.

Diamond plates do not differ that much for hone flattening either, as a 300 grit finished stone will smooth out quickly and there would be not much if any difference in the finish between a 300 or 1k stone finish and no difference in the final finish on the bevel or edge. The 400 Atoma will keep yours stones flat and raise a nice slurry.

If the stone is a finisher, down the road you will want to incorporate a Tomo nagura for a finer finish, here again some experimentation will be required. Even with Asano stamped nagura can vary in performance.

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Originally Posted by Zwilling

Does anyone know what it might be?

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Yes, this is Takashima. Characteristic color and cut.

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Originally Posted by Gasman

IMO, You now have a Diamond paste edge. It's no longer a Jnat edge. But you know what they say about opinions. LOL.

Take the edge up to 8k synthetic, Then use a Diamond card on your stone to raise slurry. This will make it the stones only slurry. From there finish on it. That will give ya a better idea of the stone. Not all the Naguras. I'm nowhere near a pro honer or a Jnat pro, but I manage to get keen edges on Jnats! Good luck.

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+1 to this. Can't really evaluate its qualities as a pure finishing stone if the edge is being further fined elsewhere (more than stropping w/ fabric & leather)...

That said, if you're getting the edges you like from the process, then that's all that needs done.

If you want to purely evaluate the stone, my suggestion would be shave off the stone. Try ending with a diamond plate raised slurry first (or suitably matched tomo, not the mejiro although that might useful to test for other reasons than evaluating this stone). Then try slurry dilution to water laps. That will let you know whether the water laps are improving your edge.

You know what the diamond edge feels like, so you can have that as a comparison to these routines.

I'm a big fan of this when people are learning Nagura progressions... stop after every progression, strop, and shave with the edge. You'll figure out what's going on with the edge (and learn a lot what you're looking to get out of each step of the process).