Rust under control?

[Marcin]

Somebody used sword to cut or moisture residue in saya started rust spot on yakiba. Please give me your opinion. I was using uchiko once per week on this spot and added extra more choji.

[Marcin]

2 more photos.

Its black now so  should be inctive but dunno whats going on deeper.

[Marcin]

So After a full year of choji I aproached blade wanting to neutralize and clean all rust.

It's not attempt to DIY polish but to protect blade from further corroding.

While removing old oil I barely used any uchiko as polish was fresh.

 

[Marcin]

So for now original photo of worst spot coming from purchase offer and again one of photos above to show what was going on with blade 3 months after purchase. You can clearly see that rust was hiden dipper then just spot on ha and started to appear at wide area.

 

 

Edited April 9 by Rawa

[Marcin]

So how this spot looks now after coating of baking soda mixed with choij? Of course coating in this particular case needed to cover wider area then only rusted. 

[Marcin]

Covering from the other side practically removed all oxidation without trace.

 

Edited April 9 by Rawa

[Marcin]

And after while with uchiko I got clean surface.

[Marcin]

And to showcase what baking soda can do with nasty fingerprint at mune I’m adding this photo. Please notice you can clearly see that area wasn’t scratched or grinded. It’s only went from red to white/gray with spots of healthy steal.

Edited April 9 by Rawa

[Marcin]

In my opinion only oiling living rust spots just helps break further already loosen rust crumbs. In my case area with black dots changes to big chunk of rust in just 3 months. Adding more photos of other „bad actors”

Edited April 9 by Rawa

[Marcin]

And now this looks way better.

[Marcin]

Now maybe kissaki with uchiko only. Kitae ware near fukura and fukura area is smoother.

Edited April 9 by Rawa

[Mister Gunto]

Nice work!

[Natichu]

Can you describe exactly what you're doing with the baking soda? I must admit I'm not quite understanding the process you're employing. 

[Marcin]

On 4/16/2026 at 7:23 AM, Natichu said:

Can you describe exactly what you're doing with the baking soda? I must admit I'm not quite understanding the process you're employing. 

I stabilized spots with „active” fresh rust and removed some „old” black patches.

You can see from the start of this thread what was going on with black dots, it suddenly started changing from 2 little dots to entire patch.

It was done only in edge area and one finger print at mune.

I have decades of experience with polishing granite so I know how easy is to make dimple.

Baking soda with choji abura. 

Edited April 26 by Rawa

[Bruce Pennington]

19 hours ago, Rawa said:

stabilized spots with „active” fresh rust and removed some „old” black patches.

You can see from the start of this thread what was going on with black dots, it suddenly started changing from 2 little dots to entire patch.

It was done only in edge area and one finger print at mune.

I have decades of experience with polishing granite so I know how easy is to make dimple.

Baking soda with choji abura. 

Marcin,

I'm with Nathaniel in that I'd like to know your process.  I can hold baking soda and choji abura in my hands .... but what do I do with them?

[Marcin]

You are making solution of both and depending on what you want to cover it’s either more of oil or soda.

1. For example on edge I went for really wet cover to soak entire area. 
-It can’t be simply cover as soda need some „move” to be active at surface. Just like on a creek there is layer between water and air. 

-after making solution and covering You have to kinda „shake in spot”

-I used small microfiber so I had full control on point.

-of course You need to be sure where You doing it and that there is no rust particles.

[Bruce Pennington]

Thanks Marcin.  I have some NCO 95s with black spots.  I'll try this method and let you know how it comes out.

[Marcin]

12 minutes ago, Bruce Pennington said:

Thanks Marcin.  I have some NCO 95s with black spots.  I'll try this method and let you know how it comes out.

I would like to try it on nco.

Doing this at nihonto is limited by space from ha to hamon line.
Above hamon on good polish You can only cover as it’s to easy to scratch.

I left 2 spots of black rust at mune.
I don’t touch something that can suddenly reactivate.

If You have to choose between removing rust and making cavity or leaving blade in current state better leave it as it is.

 

[Bruce Pennington]

Marcin,

I've gone over a 95 that has a good deal of black stains, including a permanent 4-finger print, and it's not doing as good a job as your results.  I'll say the darkest black spots have become lighter black.  But the vast majority is just slightly lighter.  I wonder if I'm not doing it the same way as you are, or maybe the difference in steels might be behind the difference in our results. 

 

I'll try posting photos tomorrow.

[Marcin]

16 hours ago, Bruce Pennington said:

Marcin,

I've gone over a 95 that has a good deal of black stains, including a permanent 4-finger print, and it's not doing as good a job as your results.  I'll say the darkest black spots have become lighter black.  But the vast majority is just slightly lighter.  I wonder if I'm not doing it the same way as you are, or maybe the difference in steels might be behind the difference in our results. 

 

I'll try posting photos tomorrow.

Thanks Bruce, I linked You cheap Nco I bought this week so I will have a lot of fun. I need to try myself on mass-produced steel.

 

I would also go for wet soak entire blade in choji and wrapping in towel as pre-soda prep.

 

It’s not professional removal, more like last resort preservation effort but it gave me results that stops year long headache :D

If not for this Aki I would still be „mostly koshirae owner” - same as 17 years ago.

Most important thing is time and repetition. 
Black rust can be deep. And soda/uchiko moves need to go with a grain.

As this is not polished blade I would go ape with uchiko too.

Adding NCO pics from auction.

I will go for sharp and clean number too.

I will go for different treatment on either side.

Edited May 16 by Rawa