working acids for etching/rust removal?

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inferno

inferno

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I just found rust spots on one of my kurosaki knives. its black but stainless clad.

and now i wonder whats a good method of removing it without removing the black oxidized coating in the process.

i have read that acetic acid/vinegar will work. or maybe work.
what about citric acid and oxalic acid?

i dont want the back coating coming off i just want to remove or neutralize the rust spots.
i have tried boiling red rusted blades to convert into black oxide.
but i have also boiled stainless clad knives and the cladding rusts when boiling it because the cladding had been worked with carbon steel tools.
 
I'd be interested to hear people's thoughts on this.

I personally have had better results with bicarb rather than acid for removing rust while leaving patina on blades, but obviously an intentional finish may react differently. If you were going for acid, I would try something quite weak initially eg. lemon juice. (I sometimes use bicarb + water + a squeeze of lemon with good results.)
 
whatever coating you don’t want coming off coat it in cheap nail polish and the edge itself too before you etch
 
bakin soda, hmm. i have to try that first i guess since it seems like the least risk. i think i'll just put some on a sponge and try to rub the rust away.
 
Lets see some pics of what we're talking about. TF Denka gets some interesting orange patina in the SS Ku finish and for me it's a huge plus and adds character. Here's an extreme example
07141429_500103bd207f7.jpg
 
Not sure how this would work for your application, (I'd probably stick with the baking soda or lemon) but there's a product called Evaporust that works pretty well and supposedly is non-toxic
 
Corradobrit1 said:
Lets see some pics of what we're talking about. TF Denka gets some interesting orange patina in the SS Ku finish and for me it's a huge plus and adds character. Here's an extreme example
View attachment 89839
Click to expand...

This is really cool! How much rust would we be talking about originally? Would you sand some off a badly rusted blade beforehand...?
 
this is what mine looks like. its has quite deep texture.

rust1.JPG

rust2.JPG
 
Last edited:
I might have an answer to this...

I've thought about this problem in the past and wanted to see if the science is true. So I purposefully rusted the hell out of a KU knife with the plans to "fix" it. Never got around to doing it, but the knife is still rusty. Will try it now and report back soon...

mPcKvHm.jpg
 
what will you try kip? acids or some rust-converter? baking soda?
 
I viewed a video of cast iron restoration where the author used various methods from severe to slow. One thing he mentioned that with solutions like vinegar they loosen up the rust but you need a scouring pad to remove it.
 
  • Scrub off any excess rust with a wire bush or scourer
  • Submerge the blade in boiling water
  • Repeat above steps until the redness is gone
  • Oil blade
There's a bunch of science involved, but it's 2:30 am here. Maybe some other time.
 
inferno said:
i have tried boiling red rusted blades to convert into black oxide.
but i have also boiled stainless clad knives and the cladding rusts when boiling it because the cladding had been worked with carbon steel tools.
Click to expand...
Oh I just realised you said this in the original post - My bad. I didn't help at all.
 
Kippington said:
Oil blade
Click to expand...

Throwing back to the other thread, did you give much thought to the oil?

I have been wondering if a drying oil is a good preservative for oxide? If the surface absorbs some and it polymerises, do you end up with a more durable finish? I've tried it on a few kuro tools - certainly doesnt hurt... but I don't know if it makes the oxide any more durable! I like to think so....
 
Luftmensch said:
Throwing back to the other thread, did you give much thought to the oil?

I have been wondering if a drying oil is a good preservative for oxide? If the surface absorbs some and it polymerises, do you end up with a more durable finish? I've tried it on a few kuro tools - certainly doesnt hurt... but I don't know if it makes the oxide any more durable! I like to think so....
Click to expand...
Yeah, drying oil seems like a good idea, but it's not a requirement by any stretch. I would go a drying oil for the first coat, giving it plenty of time to cure. Then if you want you could go over it again with a non-drying oil.
Here's the rust bluing oil process. The whole video is worth a watch, I might try something similar on knives later down the track.
 
this one also shows the process very well. i think of it as accelerated rust bluing.

 
i tried baking soda and brushing it off and i got most of it off. at least its not very visible anymore.
but there was still some red/brown deep in the pattern of the cladding.

so i tried boiling it for 10 minutes. and nothing.. the red/brown did not disappear or turn black.
on the plus side, the black cladding did not change or lose color. so this appears to be safe to do.
the edge steel turns red/blue/black though.
 
Soaking metal in vinegar will remove rust. I’m restoring an old vise right now and it’s working great. Vinegar takes longer than other acids because it’s a weak one compared to most but it’s also very gentle.
 
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