Why is it that Kurouchi knives often seem to have a flat profile?

I am looking for a flat-ish profile gyuto, 210-240mm. What I have started to notice is that the profile I am looking for seems much more common for KU knives than for stainless/carbon/clad knives.

I am not quite sure that KU (or carbon in general) is something for me because of knife care issues. But I find the flat profile (like for example the Munetoshi gyutos) veeeery attractive.

So now I have become curious: why is it that there seem to be relatively many KU knives with a flat profile? Is there a specific reason for this? Or is it part of the general KU knife aesthetics? Or are KU knives bought only by knife nuts that prefer a flat profile?

Very interested in hearing your thoughts!

Munetoshi is great, get one

Seriously - Munetoshi is indeed one of the flattest knives out there, it just happens to be a kurouch knife. Japanese knives have in general different (and flatter) profile than western kitchen knives. KU (when well done) strongly reduces risk of rust and in general reduces the area that gains patina. I helps somewhat with food release, but can cause drag when slicing stuff like meat. Aesthetics is definitely part of the game, some people love it (me) some do not.

If you do like kurouchi, than Kochi from JKI and Munetoshi are some of the finest out there with very strong '3D' structure. You will find similar kurouchi on Wakui knives too, as well as older Itinomonn knives. There are also stainless knives with kurouchi (Masakage Koishi just to name one example, there are more though), but the carbon ones are nicer IMO. There are also smooth kurouchi finishes (like for example on Carter knives). Some kurouchi does not 'hold' too well on the blade (Tanaka would be a good example).

Thanks, very useful feedback for me.
Really like the looks, still have some doubts whether it will be compatible with my kitchen routine - only one way to find out I guess...

I'm not an expert but I would guess that since a lot of KU knives are forged to shape, it would be easier to forge the profile flat than curved

There has never been a better time to get a Munetoshi knife. 20% off right now.

DamageInc said:

There has never been a better time to get a Munetoshi knife. 20% off right now.

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indeed

DamageInc said:

There has never been a better time to get a Munetoshi knife. 20% off right now.

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Is there a discount code for use at JNS or are the online prices 20% less than usual right now?

milkbaby said:

Is there a discount code for use at JNS or are the online prices 20% less than usual right now?

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November is the code.

Boynutman said:

Why is it that Kurouchi knives often seem to have a flat profile?

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It's a damn good question that I'd like to know the answer to as well. My best guess is that the reason is purely cosmetic, and that the low tip on flatter knives looks ugly if there's no shinogi line to keep the shape flowing.

For example: These two are the exact same image, only the bottom one is mirrored and has no shinogi line.



I might be alone here but it looks way different to my head anyway.
I'd love to know if there's a better reason.

Matus said:

Some kurouchi does not 'hold' too well on the blade (Tanaka would be a good example).

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I have noticed that with my new Tanaka when rubbing oil on it with a paper cloth I get some discolouration. Is there any way this could also "contaminate" the food?

Maybe it is the assumption that people buying KU knives are open enough to learning asian/alternative technique, and that people getting a polished knife might expect it to be a conventional chef knife and insist on there being features enabling rock-chopping?

LifeByA1000Cuts said:

Maybe it is the assumption that people buying KU knives are open enough to learning asian/alternative technique, and that people getting a polished knife might expect it to be a conventional chef knife and insist on there being features enabling rock-chopping?

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This was my thought I just couldn't figure out how to word it

LifeByA1000Cuts said:

Maybe it is the assumption that people buying KU knives are open enough to learning asian/alternative technique, and that people getting a polished knife might expect it to be a conventional chef knife and insist on there being features enabling rock-chopping?

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I am pretty sure that is not the case. KU finish is for the most part simply just cheaper. I think one would find very few KU knives in Japanese pro kitchens. Already because it can not be simply wiped clean because of its coarse structure. Also - on many knife types KU finish may be detrimal as it will increase the drag. There are very few KU deba or yanagiba knives for a reason. Some western users (me included) happen to like the KU either for its specific aesthetics and/or because it makes the knife a little easier to maintain.

My impression was that KU was more prevalent in tools for earlier stages of food prep - butchery, portioning at market stalls, farming and gardening?

That would make sense and go along the 'simpler & cheaper' philosophy.

And more robust - a migaki/kasumi knife would probably develop more rust problems with exposed jigane in said applications...

The discoloration (on the paper towel I suppose) is the kurouchi itself. I have handled a different knife once that behaved similarly. The kurouchi here is just a skin from heat treat on a relatively smooth & flat surface (which was probably ground after forging) and it does not hold too well on the knife. I guess that property is dependent on the cladding material and HT procedure (and that is really just a guess). My kurouchi Carter is very smooth too, but the kurouchi is very stable.

But I do not expect the kurouchi to contaminate the food. If anything you do not 'rub' it agains the food. If the kurouchi were capable of that we would not be able to buy knives with that potential. To answer that with more knowledge and less guessing we really need someone line Jon or Maxim to chime in.

I don't see a forged KU finish coming off with a wipe from a paper towel. I can use something like a bamboo chopstick to scratch a KU surface with quite a lot of force, there's no damage to the knife and none of the color transfers onto the bamboo.
I'm guessing that some knives have a kind of 'fake' KU which they use something like gun blue/patina to get the color they want.

Matus said:

(...) Some kurouchi does not 'hold' too well on the blade (Tanaka would be a good example).

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bennyprofane said:

I have noticed that with my new Tanaka when rubbing oil on it with a paper cloth I get some discolouration. Is there any way this could also "contaminate" the food?

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This was a reply to my question, it's surely not every KU knife. The Tanaka KU is also much thinner than other KU.

Some KU knives come with a sort of lacquer or surface varnish applied. Maybe even some other carbon steel knives have this, but I'm not sure. It could be some color in the surface coating that comes off too as well as the possibility of the "fake" KU mentioned by Kippington.

I think the KU finish is cheaper to make, they don't have to spend time to clean it up and make it look all nicey nice when there's a layer of forge scale covering the blade. Maybe it's also less work to grind the bevels on a flatter profile than a more curvy one?

milkbaby said:

Some KU knives come with a sort of lacquer or surface varnish applied. Maybe even some other carbon steel knives have this, but I'm not sure. It could be some color in the surface coating that comes off too as well as the possibility of the "fake" KU mentioned by Kippington.

I think the KU finish is cheaper to make, they don't have to spend time to clean it up and make it look all nicey nice when there's a layer of forge scale covering the blade. Maybe it's also less work to grind the bevels on a flatter profile than a more curvy one?

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I think you might be onto something with cost to grind a blade with a nice curve in its belly to promote rock chopping, but I bet there's also a lot of traditionalism and purism in the associated parts as well. For example, how often do you see a Western handled yanagiba, usuba, deba, or other single bevel knives? With a lot of Japanese culture, there's the "Japanese way" of doing something, and not a lot of straying from tradition in certain things.

Kippington said:

I don't see a forged KU finish coming off with a wipe from a paper towel. I can use something like a bamboo chopstick to scratch a KU surface with quite a lot of force, there's no damage to the knife and none of the color transfers onto the bamboo.
I'm guessing that some knives have a kind of 'fake' KU which they use something like gun blue/patina to get the color they want.

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No, he's right. I did a double-take the first time I washed my Tanaka KU when I noticed a few patches on the knife where the black color had seemingly given way to light gray.

I've seen pictures of "fake" KU finishes where black lacquer is literally painted on the knife by the blacksmith to give their cheap knives a more rustic appearance. I really don't think that using gun bluing would actually save any money in the process - hot bluing is a time-consuming, labor-intensive process, and it would give you a very similar (basically permanent layer of metal) result. As I understand it, the point of KU knives is that the steel gains this gray/black patina naturally during the forging process and it's just left on for the final product, rather than polished off (extra time/cost).

I was mostly talking about cold bluing, which I understand is non-toxic and quick to apply.

BTW I was getting a bit ahead of myself when comparing 'fake' and 'real' KU. There is clearly more then one kind of 'real' finish. Whats interesting to note is that a finish coming out of the forge gets easily scuffed up during the finishing stages, post heat-treat. Surely with the pitch black KU on some finished knives, they must be covering any scuff marks with some kind of cold blueing or forced patina as they cant heat it up again past temper.

The KU or firescale that comes out of my charcoal forge has a very different look and feel to the one I've seen on say a Shig KU. I'd be very interested to know what they do to it.


Forge pitting on KU finish:



No forge pitting on KU:

We would need an input from someone with more knowledge, but I think that calling kurouchi finish a 'forge finish' is not correct. kurouchi can be also forged finish, but with the very smooth KU finishes it is mostly only HT finish (scale) that was not removed after quench & temper. The KU Shigefusa above is a good example I think - that knife was most certainly ground before HT.

Are you a saying that the unpitted KU finishes are cold blued?

No, I mean when you quench steel in water or oil, then you get a thick black 'skin' on the surface - we call that kurouchi. When my carbon steel blades come back from HT (oil quench for the O1 steel for example) they look like this. If I would not grind part of that finish way, it would be called kurouchi - and that is a stock removal blade, not a forged blade.




Good example of forged kurouchi finish is Munetoshi.




If you strip the KU finish from a forged blade without grinding over the finish, than you get a Nashiji finish - shiny but not even (often seen on stainless clad blades with carbon steel core). Look for example at Kanehiro AS knives.

... at least that is my understanding on this matter.

Matus, you have to remember that many smiths do their heat treating in a forge. Would it not still be called forge-finish or firescale?

It does minimize on the pitting and look quite smooth if I forge to shape, grind all surfaces then heat-treat (in the forge). The pitting goes, however I still don't get a super dark color finish on the resulting KU. I'm quite convinced there has got to be some kind of chemical play involved... especially because there are so many abrasives involved in the post heat-treat stage, and yet knives such as the Shig have no noticeable scuffing on the finish. I may be wrong though.

That is a good point. Most probably the scale will look differently if the knife was soaking in forge than in an oven before the quench, because of the different environment during the soak.

On top of that I did not realize (being a non-native English speaker) that 'forge finish' does not necessarily means the same as 'forged finish'

My Japanese is very sub-par, but I think that 黒打ち translates as "Black strikes / black stricken" (?)

My experience is that the type of forge makes a huge difference, regardless if the knife in question is stock removal or hot-forged. This has to do with agitated atoms (rotation and vibration) and the stability of the material I think. The more rotation and vibration the more likely it becomes that the steel will interact with it's environment i.e. the atmosphere in the forge. For example: In a gas forge, it is possible to create a reducing atmosphere and this will yield a different surface texture to steel than in a scenario of oxidation equilibrium - the cleanest most efficient burning process. However None of these gas based scenarios will yield the same surface texture as in a wood charcoal forge. This is probably because there is a certain amount of surface carbon impregnation/contamination that takes place - especially during reduction - due to the charcoal, interacting with the surface of the blade. Its kind of like what happens to ceramic wares in the kiln. If you ever saw woodfired ceramics and compared them to electric fired ceramics you know what I am on about. Mind you, I am speaking as a smith not a scientist - I cannot back any of this up with formulas and equations - just my observations.

Those are very good points, I realise now that I over-simplified to issue.

And what about clay coating before heat treat, even if not honyaki many smiths use the clay for some reason, maybe the makeup of the clay makes different finishes?