What stains carbon steel?

Skeletor

Skeletor

Joined
Aug 31, 2002
Messages
544
Just what the subject says. I just got a KK and want to know what I shouldn't be cutting if I want to avoid those nasty stains. I've already learned tomatoes and potatoes the hard way. I think cutting an apple added to the stain on one of my kardas. I'm sure onions would be bad, what else?
 
meat, citrus fruits, all the foods you've already mentioned. Certain plants, which slip my mind now. Most anything can stain a carbon steel blade if not quickly cleaned and reoiled(And some even then). Personally, I've never worried much about that. Don't really think it's a knife until it starts to get a nice patina.
 
Oxygen in the air, or just about any oxidant or acid including those found in the juices of most foods. If you don't want it to stain at all, don't use it or cut only dry materials in outerspace.

As long as it doesn't turn to orange, pitting rust the grey or bluish oxide layer actually provides a little additional protection.

Just about any metal except for I think, gold, and the platinum metals rapidly form an oxide layer upon exposure to air. Just a fact of life.

Some like that formed "naturally" on aluminum, are quite insoluble and don't appear colored. (Anodizing creates colors-I think due to being thick enough to cause interference effects, but it is still an oxide coating). The oxides that form on carbon steel happen to be colored and not as durable.

If I'm not mistaken, stainless steel also forms an oxide coating, but it's chromium oxide derived from the alloy and it is colorless and very tough.
 
Firkin about covered it. :)

If you want more information, the subject of oxidation in general was discussed in the general discussion forum a copula weeks back with a LOT of information shared by the various chemists/experts in our midst. It was a good read.
 
What stains carbon steel? Using it to cut stuff. What do stains hurt? Nothing. On a no kidding user I go ahead and rub it down with lemon juice until it turns a nice, even, bluish grey. Helps keep the blade from rusting, and helps keep me from obsessing about stains. Learned about the lemon juice rub from Federico. He tends to use his khukuri a lot.:D

Sarge
 
Was about to give Sarge a hard time about this, but then realized I use a new hunting knife to cut ups teaks in kitchen until it gets a nice even patina before I'll take it out in field. SO I guess I'll jsut shut up now. :)
 
If I do the lemon juice thing will that patina stay that even grey color? I don't care if I lose that shiny silver color, it's the oil slick appearance that I don't like.
 
Originally posted by etp777
I use a new hunting knife to cut ups teaks in kitchen until it gets a nice even patina before I'll take it out in field.
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You cut down trees? How does the edge hold up to such hard wood? :)

I do the same thing as Sarge. Once you mess up the the finish you're more likely to use the blade. Of course you need a couple just for lookin' at. :D

I used grapefruit juice on an AK, then scotchbrited the raised portions of the blade. Sorta gave it a nice two toned look.
 
Originally posted by Skeletor
If I do the lemon juice thing will that patina stay that even grey color? I don't care if I lose that shiny silver color, it's the oil slick appearance that I don't like.
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It'll change when you cut acidic stuff, but you can rub it off with scotchbrite pads. It's easier to maintain than the mirror finish.
 
Gonna have to try the citrus juice bit sometime. Interested in how the patina will come out.

Course, maybe that means I should finish grinding some knives. :)

And the edge holds up well, I just have to use LOTS of little cuts to get through it. ;)
 
Oil slick effect...

That happens because the oxide layer is of varying thickness. The colors come from interferance effects like those that lead to the irridesence of a peacock feather, a soap bubble, or yes, a sufficiently thin film of oil on water.

The thicker and more even the oxide the less it will occur (Because the layer is thick compared to the wavelenth of visible light), until the appearance is an even grey or blue. Given enough time, this will happen. Since the oxide layer isn't very durable, and not totally insoluble, it can thin out again, and the effect will return.

Roughing up the surface slightly as Bruise mentions will help eliminated the interference colors because the light isn't being reflected back from a smooth surface, so all colors get a chance to interfere an equal ammount, so no one color predominates.

If the mirror finish must be maintained, then the only way to prevent the irridesence is to build up a thick enough oxide layer, either through usage over time, or regular treatment with vinegar, citrus juice or the like.

Most everyone seems to agree that a patina produced over time through use looks better than one produced by short treatments with stronger oxidizing agents.
 
Hmmm, by golly, "patinated", that's me after a couple of weeks in the field.;) Which would explain the smell.:rolleyes: Never thought to try one of them green ScotchBrite pads.:eek:

Sarge
 
Thanks for the help guys, I like this solution a whole lot more than avoiding certain tasks! I'll just use my KK and if the patina remains uneven for a while I'll try roughing up the surface a little and applying some lemon or grapefruit.
 
I recently found a brownish/orange streak at the front of the blade... Can't scrub it off with WD-40... Is it okay to leave it? :confused:



Thanks.
 
On a no kidding user I go ahead and rub it down with lemon juice until it turns a nice, even, bluish grey.
Click to expand...
Here's the effect Sarge and the others were describing:
051216.jpg

This was done with vinegar. It also brings out the temper line.
Regards,
Greg
 
Very nice photo, Ripper.
I am going to try that on one of my worker khukuris this weekend. Probably the AK or UBE.
So if I stain it with red wine vinegar and then use olive oil for protectant, can I use it to cut lettuce and make instant salad? :)
 
Originally posted by Chopsticks
I recently found a brownish/orange streak at the front of the blade... Can't scrub it off with WD-40... Is it okay to leave it? :confused:
Click to expand...

Try some flitz or some other metal polish. If it's rust, you probably want to get rid of it.
 
Aluminum does form an oxide layer on contact with air, and the oxide prevents the rest of the metal from reacting. Unfortunately, iron forms an oxide layer, and keeps rusting until there's nothing left (if it's in rusting conditions. The oxide layer offers some protection, but you still can't leave a patinaed blade out in the rain).

I'm pretty sure that gold and platinum don't form oxide layers at all, except under unusually harsh conditions. That's one reason that cheap jewelry can be electroplated with a thin layer of precious metal to make it shiny. If the elecroplate oxidized at all, it would be gone. Same thing with high end electrical components. Early computers (circa 1970's, I think) have a sizeable quantity of gold in the circuits. At one time, people did search out old computers for the gold content, though now I think they'd be worth more as a rare collectible.

Just my daily dissemination of useless info.
 
I used vineger on that KK and it looked like crap. Then I went and polished the blade up with some turtle wax and got a nice even finish. There still is a very faint, but very wide, stripe running the width of the blade across the spine and back across the other side. Does this have something to do with the temper that the vineger brings out? Maybe the RR kami screwed up or something.
 
It's been my experience that the hardened portion will be darker in color than the rest of the blade when doing a vinegar etch. that might be what you see or there was something on the blade that prevented a complete etch; might have been some oil, wax, etc. still on the blade (I think the magic stone finish might even cause this). I hit the blade I'm going to do with either steel wool, green scouring pad, or fine sand paper before applying the vinegar. I completely submerge the blade in a container of vinegar. I just keep on eye on it, looking for the result I want. If it doesn't look like it is going on even, I usually just scrub it little more while it's wet and re-submerge it.
Regards,
Greg
 
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