carbon steel/patina questions

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dudethatlikesblades

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Nov 6, 2014
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I'm gonna sound like a newbie asking this (well I am). But I have been interested in purchasing a carbon steel knife but need to know a few things:

-What is a patina? Why do some people force them on their blades? How do you apply one and will it wear off over time? Do you have to scrape off the coating off the knife before applying a patina? If someone can go into detail about this it would be much appreciated.

- What are the basic requirements to preventing/removing rust from a carbon steel blade that I should know about? (put in mind this knife might be used for food prep so if you recommend any oils...well yeah...

- As some of you might know I've been considering purchasing a kabar bk10, so if you could post some pics of yours and tell me your experiences with them it would help A lot!


Thanks in advance guys!!!
 
If you leave the coating on your BK10, you won't have to worry much about corrosion (except on the edge, and that is somewhat dependent on environment) or patina. If you remove the coating, you will have to do more blade maintenance. Patina refers to the discoloration that occurs on metals (and a variety of other surfaces) as they age. On metals, it is a form of oxidation...but it is considered "good oxidation" because it does not damage the metal as does red rust, and because it gives the surface some protection from bad rust. People force a patina for that protection, and also because they like the way it looks. One can create patterns with a forced patina that would not occur if it was allowed to form over time.
Here are a few examples:
On this knife, the patina was created by cutting sausage, and allowing the juices to sit on the blade while I ate my lunch. Notice the circles and blobs caused by the grease droplets. I cleaned the knife, and later used it to slice a couple bananas for a desert. It was interesting watching the black streaks form as I was cutting.

Here are a couple more that acquired a patina through use - primarily cutting meats and fruits.



There are some that would say that this sort of patina development is still a forced patina because it is intentional and accelerated. I don't wholly disagree with that sentiment; but I don't really think it makes all that much difference.
Here are a couple I that I forced via various methods.


(I apologize for the glare in these photos - but I don't have the option of taking pictures under better conditions this morning)

Patina can be removed - in part, or completely - in a variety of ways. Personally, I like using a little metal polish & scrubbing with wadded up aluminum foil. It doesn't scratch the blade like sanding would, and I think it does the job more easily.
 
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A patina is just staining the blade. It can be polished or sanded off. Preventing rust just takes some oil/ coating if you aren't going to use it but normal use will generally knock any rust off the blade. If not, get some fine sandpaper or metal polish and remove it like a patina you don't want. If it's really light rust you can also use a pencil eraser to rub the rust off. I live within minutes of the Atlantic Ocean and don't have an issue with crazy rust or anything. The only time I've really needed to resolve some fairly serious issue with rust was a 52100 knife that I left in the sheath for a couple of days after I got rained on. I took some 320 grit sandpaper to everything and worked up to 2500 grit. Came out looking, IMO, better than when it was new. I wouldn't have really ever done that had the blade not shown some rust to begin with.

Carbon steel knives require a different mentality than stainless steel knives. You just need to use it and not be afraid to make it look different than it came from the factory. I've found myself caring about my carbon steel knives more than stainless because once I start maintaining it it's mine.

My work, my maintenance, my diligence, and my use shows on the knife without detracting from the appearance of the knife whereas the only thing that shows on a stainless knife are dents and dings that can detract from its appearance, regardless of what caused the damage. Once I've accepted the knife is mine and will never be anyone else's I feel like a burden has been lifted and I'm free to use the knife as it should and can be used. I can modify the appearance, grips, etc. without worrying about reselling the knife later. That hurdle gets crossed quicker with a carbon steel knife than a stainless knife. Sorry for the off topic statement.
 
The bk 10 will have a very durable coating on the blade to prevent corrosion. Only the actual cutting edge is unprotected, but its not a big problem. If I see a little surface rust on the cutting edge I just strop it on leather and it removes the rust. I have the BK9, not the BK10, but same thing.

I do force a patina on my Mora knives. Use a mild acid, I use lemon juice, and apply it to the blade with a cotton ball or something similar. The results will be almost immediate. The blade will darken in a minute or so. Rinse the blade in cool water and dry. I usually do three or four applications as I like the blade to have as much corrosion resistance as possible.

You will have to touch the cutting edge up on a stone or strop as the acid will corrode the cutting edge slightly.

It will not be rust proof afterwards, but with minimal care it will tolerate more humidity without rusting.

For a blade that will see food prep use, plain old pharmacy mineral oil is the recommended lubricant for corrosion prevention.
 
Your knife already has a coating to protect from rust as has been said. Patina is a form of steel oxidation which will give *some* protection from rust. This is because patina does not "grow" like red rust opening up the metal to more moisture and oxygen. It forms a coating of sorts.

The reason stainless doesn't rust as easily is that the chromium immediately forms a hard chromium oxide coating (which is shiny and indistinguishable from the metal) upon exposure to air.
 
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Stainless can rust - it just doesn't happen as quickly as on carbon steel blades.
 
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