Restoring iron clad colour

[Lars DK]

Hi all

Being new in the sharpening game, i bought an old japanese iron clad nakiri knife in desperate need of a restoration. It had multiple 1-2mm deep chips along the edge and a bit of rust here and there on the primary edge.
Thus - I figured it would need a fair bit of thinning to reach a proper result.
So i found a 120 grit stone and got working. The result was pretty good for a first try i think. I got the primary edge down to remove all but a now very small chip right at the heel. No pictures included, as i dont have enough posts to allow it at this state.

However - the knife had various high-points up in the dark iron cladding part that i also hit with my thinning.
So now i am left with a some shiny steel spots in my dark iron clad.
- Is there any tricks to restoring this dark grey colour afterwards, or am i stuck with my uncautious thinning?

 

[stringer]

Hi all

Being new in the sharpening game, i bought an old japanese iron clad nakiri knife in desperate need of a restoration. It had multiple 1-2mm deep chips along the edge and a bit of rust here and there on the primary edge.
Thus - I figured it would need a fair bit of thinning to reach a proper result.
So i found a 120 grit stone and got working. The result was pretty good for a first try i think. I got the primary edge down to remove all but a now very small chip right at the heel. No pictures included, as i dont have enough posts to allow it at this state.

However - the knife had various high-points up in the dark iron cladding part that i also hit with my thinning.
So now i am left with a some shiny steel spots in my dark iron clad.
- Is there any tricks to restoring this dark grey colour afterwards, or am i stuck with my uncautious thinning?

Use the knife and let a patina form naturally. Or force a patina with something acidic like coffee, orange juice, vinegar, mustard, etc.

 

[kdizzog6]

The easiest thing would probably be using some sandpaper to make it uniformed. Maybe 320-500 grit to get it clean then some high grit to make the finish look a little better. Followed by slicing some onions to get a patina back on it.

 

[Lars DK]

Is the dark part on a iron clad knife simply just a thick layer of patina?
I dont really mind if its not complerely uniform - But as of now, the difference between dark grey and shiny metal is a bit much.

So i could simply force a patina on the highspots - This would probably require multiple rounds i suppose?

 

[stringer]

Is the dark part on a iron clad knife simply just a thick layer of patina?
I dont really mind if its not complerely uniform - But as of now, the difference between dark grey and shiny metal is a bit much.

So i could simply force a patina on the highspots - This would probably require multiple rounds i suppose?

Just depends on what you're going for. But patina will subdue the shininess and even out the finish. And it will have the added benefit of inhibiting future rust.

 

[Lars DK]

My main concern about removing all the dark on the iron clad to start over would be if im able to get it looking nice and even dark again. The existing dary layer seems rather thick and hard. I suspect it would take quite a sanding to fully remove it.

 

[Blumbo]

I think it would be helpful if you took pics to help us understand what you’re seeing. It could be kurouchi, kasumi, patina or etching youre referring to

 

[Rideon66]

Are you speaking of the Kurouchi finish? https://knifewear.com/blogs/article...MeHQENA_iw6Bu2cRJdwghQihm710ndrvoLNnjL6moRnM4

 

[Lars DK]

Since i have now exceeded the 5 post limit, i guess i would be allowed to add a before and after image here

Initial state when i bought it.

After thinning - Seeing the before and after besides each other, i see that i might have been a bit excessinve in my thinning by making the primary edge go further up as well, thus making it thinner longer upwards than the 1-2mm i have removed from the depth in total.

Polished high-points in the dark areas are rather obvious here i guess. Can i restore that by forcing patina a number of times?

 

[aporigine]

Since i have now exceeded the 5 post limit, i guess i would be allowed to add a before and after image here

Initial state when i bought it.
View attachment 351476

After thinning - Seeing the before and after besides each other, i see that i might have been a bit excessinve in my thinning by making the primary edge go further up as well, thus making it thinner longer upwards than the 1-2mm i have removed from the depth in total.
View attachment 351477


Polished high-points in the dark areas are rather obvious here i guess. Can i restore that by forcing patina a number of times?

Maybe gunsmith’s cold-blue or parkerizing juice?

 

[Blumbo]

Since i have now exceeded the 5 post limit, i guess i would be allowed to add a before and after image here

Initial state when i bought it.
View attachment 351476

After thinning - Seeing the before and after besides each other, i see that i might have been a bit excessinve in my thinning by making the primary edge go further up as well, thus making it thinner longer upwards than the 1-2mm i have removed from the depth in total.
View attachment 351477


Polished high-points in the dark areas are rather obvious here i guess. Can i restore that by forcing patina a number of times?

That dark stuff is kurouchi which is the dark oxides that form during the high temps of forging. The patina that forms during use usually does not reach a similar color because the oxides that are formed are different. It’s a little more challenging to restore and most smiths spend a lot of time finding a particular solution that provides a consistent kurouchi. I’ve heard some people try gunmetal bluing for darker oxides but I doubt the result will be the same

 

[HumbleHomeCook]

Good for you to tackle a project knife.

Either sand it off or accept it as character. I'd opt for the latter.

 

[deltaplex]

That black iron oxide from heat can't be replicated, but you can even it out into a more aesthetically uniform finish through chemistry, not unlike a large number of kurouchi finishes utilized by japanese smiths/sharpeners/vendors.

 

[mengwong]

I'd opt for the latter.

Agreed. Loss of kurouchi is quintessential wabi-sabi.

But if you really need it black, there’s always the Sharpie trick!

The other Sharpie trick.

 

[VincenteFox]

I really don't think the polished off parts look bad. Just looks like a knife that's been used, which they should be.

 

[Lars DK]

Thanks for the inputs and new word learned - kurouchi
I guess i figured that by the toughness and thickness of it, the kurouchi was more than just a patina layer. But also i was more focused on trying to keep a consistent and more shallow angle in the thinning than keeping the kurouchi intact.

I will try and force patina on the polished off parts to reduce it slightly and accept its general look i guess

 

[kujaku]

When I first started sharpening, I accidentally removed off part of the kurouchi due to the wrong sharpening angle, and I didn’t like the way it looked, so I decided to remove it. I still have that Murata knife. While removing the kurouchi was easy, it ended up highlighting the hammer marks and low spots, making it more prone to rust.

After reading your post, I remembered that knife and conducted an experiment to dye it black. I mixed vinegar and hot tea in a 1:4 ratio and soaked the knife for about 20 minutes. Unfortunately, the cladding part showed minimal reaction, but the hard steel part dyed beautifully.

 

[Lars DK]

Good to hear i am not the only one making this kind of mistakes. Or - I guess not a mistake for me as such. I was aiming for reducing the angle, but had not expected the highpoints to be so high.
I have made somewhat the same conclusion after looking more at it. If i sanded it down, it would become rather strange looking because of the hammer marks here and there. I guess that is also some of the charm of it though.

I tried to force patina twice today with mustard. It definately had more effect on the primary edge than on the kurouchi. Not much reactivity on that part.

Just sanded the handle lightly and applied some oil. Besides the messed up kurouchi i am happy with the result. Its not all bad though. It definately looks and feels like something that has done a bunch of work (which is probably true as well)

 

[HumbleHomeCook]

I think this happens to all of us who take on these kinds of projects. I've gone up into the kurouchi (also known as KU) finish on more than one knife.

Also, on a lot of these knives, the KU will start to fade or even come off over time with use and washing. Some are more resilient than others but it happens.

 

[Absolute Buffoon]

Yeah, there's no great way to recreate the kurouchi finish. Imperfections and constant change, whether created by you or the smith, on purpose or by mistake, are part of the beauty of iron clad kurouchi knives. Embrace the wabi sabi! It shows a history of your work, your learning, and your journey. Each landmark need only be a temporary stop on the road to your next journey, or whatever philosophical description most tickles your pickle.

Anyway, I'd just keep it. Removing the KU is viable, but there are a whole lot of variables concerning the cladding underneath. If it comes rough with big enough pitting, it can be really hard to dry off and end up harboring tough to reach rust spots. It also might patina super nicely, or it might have trouble making a patina at all. It might be pleasant to look at or polish up really well, or it might not. It really depends on the smith and the forging process, and there's far less experiential information on most smiths' cladding than for grind/weight/f&f/etc. If you choose to remove it, just don't go in expecting a specific outcome. Or maybe try it for science! Just know you might regret your life's choices though...

 

[mengwong]

Years from now, even after you have stopped using it on a daily basis, you will keep this “ruined” knife in a special place in your kitchen, and every time you handle it, you will be briefly suffused with the memory of this period of your life when you were first learning to sharpen; like an old perfume, or a madeleine.

 

[Cliff]

I think you've done a great job and would not stress over the KU. You've restored this really well. But, as others have alluded to, I believe KU can be formed a number of different ways. That does not look like forge scales to me -- though I am not remotely an expert. I would look into the gun bluing or parkerizing juice

 

[M1k3]

If you want to try to restore the Kuruouchi, this guide should help out.

https://mypeculiarnature.blogspot.com/2014/08/quick-rust-bluing-back-in-black.html?m=1

 

[Lars DK]

If you want to try to restore the Kuruouchi, this guide should help out.

https://mypeculiarnature.blogspot.com/2014/08/quick-rust-bluing-back-in-black.html?m=1

Seems like a interesting technique - Generating rust and turning it into oxide simply by boiling it. I would have thought that much higher temperatures etc. was required for such reactions.

I guess it could be possible to brush on something to generate rust on the KU part and then boil to convert to oxide. Would probably need some polishing and sharpening afterwards though. Might be tricky to protect the handle, boiling the blade right next to it.

 

[deltaplex]

If you want to try to restore the Kuruouchi, this guide should help out.

https://mypeculiarnature.blogspot.com/2014/08/quick-rust-bluing-back-in-black.html?m=1

This isn't my procedure, but this is my method to even KU out.

 

[Lars DK]

This isn't my procedure, but this is my method to even KU out.

So you have tried this on knifes? The handle is the more tricky aspect of this i think - Not to ruin it by moisture and steam from the repeated boiling right next to it. In my case, the rust that needs submerging in boiling water, would be only like 1cm from the ferrule. Not sure how to handle that, if i would attempt this precedure.
I dont feel like its super needed for the knive as such - However, right now i am a bit curious on trying this technique of converting 'bad' rust to 'good' oxide.

 

[Rideon66]

Going to guess, but that handle may not have any glue or epoxy holding it on. If so you can easily knock it off.
https://youtu.be/bHKAZ864WpI?si=oNg8H6uG57iR5-E-

 

[deltaplex]

So you have tried this on knifes? The handle is the more tricky aspect of this i think - Not to ruin it by moisture and steam from the repeated boiling right next to it. In my case, the rust that needs submerging in boiling water, would be only like 1cm from the ferrule. Not sure how to handle that, if i would attempt this precedure.
I dont feel like its super needed for the knive as such - However, right now i am a bit curious on trying this technique of converting 'bad' rust to 'good' oxide.

Right, yes I have. I'd take the handle off for any of this kind of work, I haven't come across a Japanese made knife that you couldn't get the handle off of in one piece through some combination of hitting/pulling/changing temperature. It is possible to do this without removing the handle, it's just a lot more fiddly.

 

[Lars DK]

Going to guess, but that handle may not have any glue or epoxy holding it on. If so you can easily knock it off.

I hadnt actually even thought of removing the handle as a viable option - Great input

 

[Lars DK]

Right, yes I have. I'd take the handle off for any of this kind of work, I haven't come across a Japanese made knife that you couldn't get the handle off of in one piece through some combination of hitting/pulling/changing temperature. It is possible to do this without removing the handle, it's just a lot more fiddly.

Seeing/hearing that its probably somewhat easy to remove the handle, that would obviously be the way to go.
Its clear that i am a rookie in the japanese knife-area. I would have thought that removing the handle would definately break it and require a new handle.

Well well well.. I might go about trying this out, just for the fun of seeing that chemistry trick do its magic.

I see a possible pitfall in warming the knife up too much with a heatgun? I guess its not a problem to get it ie. 100 degrees - But where is the limit on this? Do i risk ruining the knife, in the process of drying the rust over and over?

Also - Has it been possible to contain the rusting to the KU-area? Did you use nail polish or other tricks, or did you simply just brush the KU-part with corrosive fluid?