Carbon V Observation

Kodiak PA

Gold Member
Dec 3, 1998
Just a small observation that I noticed today. My wife needed a large knife to shave the bark off of a pineapple. I offered her my CS Master Hunter with Carbon V blade. It worked fine. I told her to rinse the blade and I would put it away later. About 3 hours later when I grabbed the knife the steel was sporadically stained and rust was already starting to appear. Can rust form that quickly? It was obviously surface stain/rust since some Metal-Glo removed the stains easily. Could someone comment on this for me. Does Carbon V stain that quickly or was it becasue of the acids in the fruit? After polishing I loaded the blade up with Tuf-Glide.

One thing other thing I noticed was that when I touched up the blade on my Spyderco Triangle Sharpmaker it became razor sharp in less than 2 minutes. That was a plus.



I work in a heavy equipment shop and I have seen rust forn on cast iron in a matter of minutes...I know it ain't knife steel....but it is sorta close...Most noticeable on freshly machined heads that have just been given a wash...the surface rust will form as fast as the water evaporates it seems...

It might have been the acid. I once sliced up a lemon at an outdoor party with a Beretta Airlight folder. I don't know what kind of steel the blade was, something cheap. At any rate, it took me several hours to get around to cleaning the knife off properly. By the time I finally did, the pivot was so sticky that I needed two hands to open the knife (the damn thumbstud fell off and I'd been flicking it open) and I had to take it apart to clean it. The blade was pretty severely stained in a couple of small spots. I never tried metal-glo on it, only a soapy sponge, and that definately did nothing for it. Not that I was heartbroken or anything, but that definately stuck in my mind. Since aquiring nicer knives, I'd be a little more hesitant to offer to slice the lemons or limes.
Without digging out my chemistry books, I don't think that there is any difference between staining from acid fruit juices and rust - it's all oxidation.

In my experience (mostly Blackjacks, some CS), "carbon" steel (not "stainless") does indeed oxidize at a remarkable rate if not kept very clean or if exposed to acidic substances. I once gave my Blackjack Model 5 subhilt an accidental bluing job by using it to cut an onion. The flip side is that these steels are in a class apart in terms of edge-holding and ease-of-sharpening. I haven't used the particle steels, but certainly no other stainless I've seen can take an edge as easily as my Blackjack or hold it so well (it's in cryo-treated 0170-6).

OK, I gotta go...all this talking about Blackjack (R.I.P.) is making me teary-eyed...maybe it's just the onion


(Why else would a bear want a pocket?)
Yeah, acidic fruit will definitely oxidize a steel like that pretty quickly. On some steels, the black "bluing" type patina seems to appear almost instantaneously. I kinda like it on a using-knife, like battle scars.

This brings to mind a posting on the boards from Member Howard Wallace on March 21. Mr. Wallace stated that the first thing he did when he got his blackjack(A2 steel) was to rub it down with lemon juice to give it a nice oxide coating. Now the knife has the same color as an old carbon steel kitchen knife. I hope this helps.

On March 21, Member Howard Wallace posted saying that he Rubbed his Blackjack(A2 steel) down with lemon juice to give it an oxide coating. It gives the blade the look of an old kitchen knife.

I've used the Cold Steel Elk Hunter with the carbon 5 blade on several moose. The bloody blade had a rust stain on it after about 3 hrs. I like how easy it sharpens and holds an edge, but it's not a saltwater knife for sure. It seems to compare with 1095 in edge holding, staining and ease of sharpening.
My notoriety precedes me.

A fresh water rinse and wiping dry should prevent the yechhy red oxide. The black oxide will still form, but will not hurt anything and actually protects the blade from further oxidation. At one time I knew the chemical forms of yechhy red and black iron oxides, but I forgot. It's back there in one of my texts, if I can find it.
Pineapple, eh? Trying to pretend you are in Hawaii, not Alaska, Greg?

I have heard of people (I think from rec.knives on usenet) soaking their carbon steel blades in lemon juice to achieve this patina.

And you got it for free!

(And I didn't send you that knife for it to look pretty! USE IT!

Clay Fleischer

Picked the wrong week to quit sniffing glue...

[This message has been edited by CD Fleischer (edited 04 May 1999).]

[This message has been edited by CD Fleischer (edited 04 May 1999).]
OK Clay,
I'm going to go rub an onion on it right now!


I have found a web page that tells about rust and black rust I will post it as soon as I can find it again.
What you're discribing between the red rust and black rust is the difference of one oxigen atom. One is ferric ox-ide, and the the other is ferric ox-ate. Which if red is rust, and if dark, is tarnish. I don't remember which is which. Blueing is a form of tarnish that forms a coating that resistes rust. -Brian
What you are experiencing is surface oxidation which Metal Glow (Which is really Flitz or damn close) can readily get rid of. Leave is too long and it will work it's way into the metal. The main ingrediants to rust are liquid (Water) and Oxygen. Othe acids and/or salt only speed the process.

Any iron has bits which are positive and bits which are negative caused by impurities and stress, and so electrons can move around. Once iron gets wet this takes place: Fe(s) = Fe(2+) + 2e- as well as 0.5O + H O + 2e- = 2OH- 2 2 The electrons from the first reaction flow through the iron (which is a good conductor) to take part in the second reaction. The ions produced by both reactions then react: 2Fe(2+) + 2OH- = Fe(OH) (s) 2 then a further reaction takes place with O(2) from the air dissolved in the water. 2Fe(OH) + H O + 0.5O = Fe O + 3H O 2 2 2 2 3 2 The Fe(2)O(3) is the rust. So for rust you need air and water. Salt also helps to speed up the reaction because it makes the water a better conductor so the flow of water increases.

Suggestion? Head over to the BF store and get Tuf Cloth!

Best Regards,
Mike Turber
BladeForums Site Owner and Administrator
Do it! Do it right! Do it right NOW!

I did use Tuf-Cloth on the knife but I guess no metal is impervious to rust. After I cleaned off the oxidation I loaded it up with Tuf-Glide and rubbed it in with Tuf-Cloth. It seems that this is part of Carbon V's make up. I'll see if it happens again. I will probably clean the knife quicker next time or just let it oxidize.


I looked up some of this in my chemistry texts. Red rust is the hydrate form of iron oxide, which is Fe(2)O(3) with a variable number of water molecules bonded to the iron oxide molecule. The chemical reaction that forms rust gives off hydrogen as a byproduct, which is used to start another reaction to form more rust, making it sort of a chain reaction. Iron molecules will migrate to the site where rust is forming to feed this reaction. This is why red rust is bad; the iron molecules will move from one place to another, creating a weak spot in its place.

Black rust is iron oxide with no water molecules bonded to it. I believe the chemical formula is Fe(3)O(4), I could be wrong on this, as I couldn't find a definite formula of black rust. Red rust is amorphous; black rust forms a hard crystalline solid which will form a coating on the surface of the metal to block the water and oxygen from attacking the iron. I think acid speeds the oxidation of iron so the iron oxide will quickly form a crystal structure and not be allowed to absorb water and become red rust. That's why citrus fruits and the like will blacken your blade. Hope this information helps.