Restoring a Kasumi Finish?

Kitchen Knife Forums

Help Support Kitchen Knife Forums:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
DDPslice said:
I like to use slurry, with jnats (any stone) the slurry partials are meant to break down finer and finer. Also when I'm on my finishing polish 8k+ I will go over the entire knife, it just leaves it silky smooth. And I test the smoothness as a wipe it with a cloth in my hands. When it slips through I know I'm done.

also please only use food safe items unless you are a chemist.
Click to expand...

apologies * i don't use any oil, just water
 
Asteger said:
I haven't tried WA with camellia, tho maybe with mineral oil. I've tried nat stone powder (uchigumori) with oil and preferred my usual water method, I think as it was easier to see and keep track of progress.

Problem with using oil with your stone slurry, if you don't have powder, then how will avoid oiling up your stones? Usually you'll generate some slurry with some means, and you won't use oil for that, and then you'll apply the slurry to the knife. To me the oil method only works if you have powder, natural or otherwise.
Click to expand...

I mop up normal, water-based slurry from the stone with a cotton ball then place a drop or two of camelia oil on the blade along with a spritz of water before polishing. Didn't have enough time last night to comment conclusively on results. I definitely do not oil my stones.
 
Tried using the slurry from each stone in a sharpening progression as I finished with the stone to polish the rest of the blade and after each grit blending with a scrubby paying particular attention to the transition between the sharpened area and blade face. Repeat through each stone and end with micro mesh. This was to re-finish after some thinning.



 
King 800
Uchigumori fingerstones
Nakayama on the edge
Buffed up the migaki finish too











Giving her a little love before BST
 
Thinning a Shig. Thought I'd take a photo of each side as a comparison. 1
Fresh off the stones and one refinished after the stones. Enjoy.


Unfinished side:


Finished side.
 
do you like the look of 800 before going to the polish? Are you able to distinguish the kasumi from the marks? Btw did you ever get those pads?
 
DDPslice said:
do you like the look of 800 before going to the polish? Are you able to distinguish the kasumi from the marks? Btw did you ever get those pads?
Click to expand...

Very much so.. Often tempted to leave it at 800 because it looks so nice
 
Got the pads but I think you can get a better result with good quality wet & dry
 
Badgertooth said:
Thinning a Shig. Thought I'd take a photo of each side as a comparison. 1
Fresh off the stones and one refinished after the stones. Enjoy.
Click to expand...

You just have all sorts of good work out there! What's the handle on this Shig? It looks good.
 
Which pads in particular? I never got on well with micromesh, but rather liked 3m microfine following an 800 grit.
 
Yeah, micromesh. Not sure if it's a technique thing and I'm doing it wrong but I get a better result from sandpaper.
 
Micromesh starts @ 1200 grit, so it does not quite replace wet sand paper - could that be part of the issue?
 
BadgerTooth>
"As an aside, I saw on the JNS that WA powder is best used with camellia oil and I tried it... Vastly different and more refined finish than using it with water. Which poses an interesting question: what would happen if you used stone slurry with camellia oil?"

Z.. I believe that White Alumina is the abrasive used in the making of some of the Japanese Whet Stones.

Asterger> " Problem with using oil with your stone slurry, if you don't have powder, then how will avoid oiling up your stones? Usually you'll generate some slurry with some means, and you won't use oil for that, and then you'll apply the slurry to the knife. To me the oil method only works if you have powder, natural or otherwise.

Z.... Most of the time, when flattening the stone, I collect the slurry in a small container and after a while... it dries and cakes up. I also have a small container when I collect all the slurry when washing knives and stones. Wasteful to throw it away and besides, it may choke up the sink/ drainage pipes eventually. THe second container is not "pure slurry" as it has metal filings form the kniives. Useful for general cleaning

Will be looking for a mortar to pound and make some polishing powder from old stones or that is too thin.

BTW bought some wa powder and i find that putting some on my cleaning cloth ( before storing the knife) which has been laced with camilia oil does remove slight oxidation . i Keep the cloth for future use. Only caveat is to wash the knife thoroughly before each use.

Have fun...

D
 
Sorry to bring up an old thread but it’s been really helpful for tips on producing an even kasumi. Thank you posters!

Another question for you guys, any tips for a kasumi on the bevel on a knife with a straight line KU finish? I’d love to keep the line straight if possible.
 
Use a thick tape to protect the KU and preserve the line you want to keep. Proceed as normal with your preferred polishing method.
 
Luftmensch said:
Use a thick tape to protect the KU and preserve the line you want to keep. Proceed as normal with your preferred polishing method.
Click to expand...

Just a little warning - depending on the kurouchi finish and the type of the tape, quite some of the kurouchi may come off when the tape will be removed.
 
^^
This is true and also try to keep the KU side of the tape dry. If water gets under the tape and you don't dry it, you can get a faint rusty outline (don't ask me how I know).
 
Matus said:
Just a little warning - depending on the kurouchi finish and the type of the tape, quite some of the kurouchi may come off when the tape will be removed.
Click to expand...
Yeah, that's what I was worried about with adding the tape. I've done that on another knife before and it pulled off the KU.

Maybe I will just have to go without a straight line anymore.
 
Perhaps find the least sticky tape you can find and use it on a small portion of the knife. See what happens? KU is not indestructible but I have found that it is pretty resilient when done well - after all it should be designed to withstand years of cutting, cleaning and contact with acidic foods. For what it is worth, I have no trouble with Nitto PVC electrical insulation tape.

If you are sure your KU is the fragile kind... and you are desperate to maintain a sharp line between the KU and blade polish, you could consider protecting the KU with a thin resilient sheet. Cut the profile of the KU out of plastic (or heck... cardboard) and use bulldog clips at the spine to hold it onto the KU surface. Never tried this so I don't know how well it would work... but I imagine it ok for a small amount of finger polishing? Maybe oil up the KU face with a food safe oil to prevent rusting?
 
"after all it should be designed to withstand years of cutting"

I think KU is rather a "non-finish" - hardening scale, or chemichally done to mimic that.
 
As Robin said. The KU is not a real 'finish'. On top of that many JP knives have 'kurouchi' done with gun blue or similar agents. Kurouchi is never going to 'last' forever. Even the nice gritty ones like the Kochi line has will not withstand hard rubbing when washing. I have seen the knife in person after a few months in a pro kitchen. Looks more like nashiji today. Nothing wrong with that.

In general I would recommend not to try to loose sleep over kurouchi falling off. It's simply part of the life cycle of given knife. Different kurouchi finishes do indeed behave differently - some will fall off in larger chunks that does not look so great, others will gradually wear off. In a home use with gentle care some will last a long time.
 
I both agree and disagree ;)

It is easy to pass it off as the absence of polishing... while this is true in a strict sense, it over looks the deliberate actions taken to create the oxide layer in the first place. It is a deliberate aesthetic choice.

I think it is a misnomer that it is simply a byproduct of forging that was not removed. Achieving a deep and stable KU finish is not an accident. J-blacksmiths deliberately go out of their way to make a deep, uniform and robust KU finish. I believe there are many ways it can be done and blacksmiths keep their process as a trade secret. If you get to handle a kuro blade from a top blacksmith (or a plane or a chisel for that matter), you'll appreciate that it is a controlled process.

All that said... "What's in a name"... I am sure there are all sorts of black, semi-stable oxides that are passed off as kurouchi. But for instance, I would not really consider black rust (e.g. gun bluing processes) as a proper KU finish.
 
(But yes, in any case... be it the best example or the worst... it is a 'fragile' feature that can be worn away)
 
Well sure. I spoke to a popular japanese smith a couple of weeks ago and he confirmed that yes most do chemichal KU, but the "best" one was to be had with leadbath heating pre quench. I can do a pretty good one with using coal dust when heat treating with my electric kiln too, but I wouldnt really call it going great length or charging any premium for it.
 
Speaking of the devil... this blacksmith uses graphite in a lead bath (turn on captions). :)

I agree - as I understand it, creating a KU finish is done before the quench. If the smith did not want a KU finish, this step would be skipped. This is where the methods vary. I am sure many smiths probably use lower tech materials and processes (than in the video) more inline with traditional processes.
 
Yea, like he says, he uses graphite primarily to avoid the lead sticking to the knives ;)

There's no skipping the heat treatment steps, but it can be done in different ways. The blade needs to be heated in some way, cooled in some way, and tempered in some way. Sometimes forging surfaces and some scale is left on too.
 
Matus said:
As Robin said. The KU is not a real 'finish'. On top of that many JP knives have 'kurouchi' done with gun blue or similar agents. Kurouchi is never going to 'last' forever. Even the nice gritty ones like the Kochi line has will not withstand hard rubbing when washing. I have seen the knife in person after a few months in a pro kitchen. Looks more like nashiji today. Nothing wrong with that.

In general I would recommend not to try to loose sleep over kurouchi falling off. It's simply part of the life cycle of given knife. Different kurouchi finishes do indeed behave differently - some will fall off in larger chunks that does not look so great, others will gradually wear off. In a home use with gentle care some will last a long time.
Click to expand...

Thank you for all the tips, guys! I think I just need to "get over it". Like you said, it's meant to be used... not a museum piece.
 
RDalman said:
There's no skipping the heat treatment steps, but it can be done in different ways. The blade needs to be heated in some way, cooled in some way, and tempered in some way. Sometimes forging surfaces and some scale is left on too.
Click to expand...

True that! Sorry. I was not clear in my previous post. You would not skip any of those essential steps (forging -> quenching -> annealing/tempering). And true! I am sure many Kuro finishes are just a by product of these processes (particularly textured ones with forging scale). But I am sure it is not unanimously so....

For some japanese woodworking tools and kitchen knives the KU is so fine i think the process is more like: forging -> "something" -> quenching -> annealing/tempering. That "something" is non-essential and can be skipped depending on the intended finish. For instance it might be a method to oxidise/decarburise the surface metal? I dunno?

I haven't encountered good sources documenting how a fine KU finish is made. If anyone out there has a link, I'd love to have a read!


I don't mean to come off as stubborn and dogmatic :p but some finishes are just too darn fine to be anything but a conscious effort. Check out these Iwasaki and Shigefusa kiridashis. You can see grind marks from shaping the kiridashi underneath the KU. The KU is suuuuch a nice and even (almost power-coat) finish. It must have been created in controlled conditions between forging/shaping the tool and heat treatment?
 
You must log in or register to reply here.

Latest posts

Back
Top