Facts about black oxide/blued finishes?

This topic stems from existing debate that people have been having on the internet about blued blades for food preparation. Some people are worried that a blued blade may not be safe to use on food, as it may impart some toxic particles. The same kind of scrutiny has been applied to the black oxide finish that ESEE (and others) are now using.

I'm a chemist, so this stuff has piqued my interest a bit. However, transition metal complexes (and their toxicities) are not my area of expertise. From what I know, the chemical composition of the black oxide on the surface of the steel is based on the type of process that is used to apply it. High-temperature processes oxidize iron to Fe3O4. This is essentially the same thing that happens when a carbon steel blade acquires a natural patina. The low-temperature industrial processes actually deposit a layer of a copper/selenium, which is an entirely different process.

I've seen/heard a lot of comments about these dark blade finishes and food, but I don't ever see definitive information. I cut up some potatoes with my PR4 the other day, and did notice that some of the black color rubbed onto the potatoes. My intuition is that it's no big deal, but I'm in search of some facts to back it up.

So, I'm curious how the black oxide finish is applied to ESEE knives? This is obviously a question for the bosses (@Jeff Randall?), but it's also an interesting point of discussion for us users. I think if we can demonstrate that the blackening process to make the black oxide finish is chemically identical to a natural patina, it will dispel the worries that some people have.

Final note: Anecdotal comments like "I use my blackened/blued knives on food all the time and I'm fine" are not helpful. Sometimes the effects of toxins are imperceptible on a macroscopic scale or over a short amount of time.

 

My cleaver stopped transferring coating after a few days. I’ve been using my cleaver for a few months and the coating hasn’t killed my yet.

 

I’m interested as well

 

I contacted Birchwood Casey once, and asked them. This is the response I got from them:

 

Coolbreeze, I think you asked me about this once on another forum, iirc, and I posted the above

 

Hey guys, this is a the first time I've heard of a knife with an oxide/blued finish having a potentially toxic side effect. While I'm no chemist, I do have four semesters of chemistry under my belt. Two were organic and scenarios like this were a common theme in the laboratory and lecture. If Fe3O4 is the source of your concern, you would have to be ingesting an awful lot of your knife blade in the form of oxidized iron to make you ill.

I would ask not if a blued finish could make you sick so much as I would ask what sort of salt (I'm assuming there's some sort of ionically bound compound for the oxidation process, like some gun blues use) is being used to produce the finish. Perhaps, if the salt contained a halogen or some other element you wouldn't want to eat and you were using it to prepare food which was very acidic or basic, then you'd have something to worry about. I got some concentrated chlorine on a Kershaw with a "blackwash" finish and it smudged it a little from the reaction that occurred. But it's my opinion that if you're eating something that concentrated, acidic or basic, your problem isn't the oxidizing agent on your knife blade.

I think what @The Warrior posted is good advice. To each their own. I know what I do. What you do really isn't my business.

 

Correct. We have talked about it before. I've been doing more research since then, and I learned a bit about the different processes that impart a black oxide finish. I'm curious which methods are used over at Rowan.

Fe3O4 (aka magnetite) is basically the bluish/blackish oxidation that we call patina. It is the same thing that is created during the high temperature processes to impart a black oxide finish. The high temperature processes use a strong alkaline solution (hydroxide salts) and nitrates/nitrites.

As for the bolded part, my black oxide coating smudges when eating potatoes, which aren't super acidic or basic. But it probably isn't any more or less of a big deal than using any carbon steel knife with an acquired patina on food. Also, there shouldn't be any oxidizing agent left on your blade (definitely not after some use and a wash), only the ferrous-ferric oxide film that makes the finish.

 

I probably should have been a little less lengthy. The above bolded section is at the heart of what I was getting at. If the process takes place under an extreme pH and temp, I would think it would take an even greater pH and/or temp to cause the coating to break free. So was it the iron in the patina that was that a concern or just anything used in the process as a whole? I'm not trying to be thick-headed or smart. I've been told I know just enough to make me dangerous. I had a lab instructor that wanted me in a red lab coat so that he could keep tabs on me at all times. Thanks for taking the time to respond.

 

The bolded is not necessarily true. In fact, the trend is the opposite. Chemical reactions are driven (in large part) by thermodynamics. If a reaction requires a lot of energy input to occur (non-spontaneous), than the reverse of the process often takes little prompting (spontaneous).

I'm not concerned about the iron in the patina. I'm concerned about whether the black oxide is in fact Fe3O4 or if it is a copper/selenium amalgam (formed by low-temp industrial processes). In the latter case, I believe the coating/finish is no longer iron-based.

Color-coded lab coats? That's not a bad idea!

 

I am interested as well. I think what most black oxide finishes are acid etched and tumbled.

I think an importartant part of your question was self answered though, imho. "Anecdotal comments like "I use my blackened/blued knives on food all the time and I'm fine" are not helpful. Sometimes the effects of toxins are imperceptible on a macroscopic scale or over a short amount of time."

Unless you are using the knife as a kitchen knife, using it in the field would likely never build up enough toxins to be harmful, even in an extended situation. Of course thats conjecture and im not educated in the matter, but for the average user that might be an important point to consider.

Now, if we are talking about using one at least every day for the very long term it would obviously be more important.

Anyways, i am interested in the answer, although the exact methodology might be a bit of secret formula stuff. Good question!

 

Interesting topic. I've searched high and low on various forums, and have not found a definitive answer.

So far, all of my ESEE knives are powder coated and used for camp tasks that rarely come in contact with food.

I plan on getting 1-2 smaller Camp Lore knives (CR 2.5, JG3) to start, and am wondering if I should buy the un-coated version as these will be used as food prep/field dressing game.

Has anyone noticed any metallic taste when using a black oxide knife with food (apples, etc.)

 

On a side note of food prep. I don’t have a good solution for the issue.. But from what I understand the micarta scales are not the best for food prep... Soneehing about retaining germs etc. SO the answer would be to go with something with The G10 type scales.. But that super limits you option and if you are worried about the Black oxide then that could really be a problem....


On the Black oxide coating.. i don’t think we are going to get a answer out of @Jeff Randall or @shaneadams90 do to obvious trade type secrets...
So the bigger question I would like to know from the chemist folks...
@CoolBreeze135 paging
If there is a concern over the coating could said coating be easily removed? I would assume depending on how it was applied the process would likely be different. But could someone simply just remove the coating from the cutting portion of the knife that would contact your food?? Again knowing nothing about chemistry would there be any safer household chemicals that might do the job?? I seem to remember running a cotton swab of rubbing alcohol over a Black oxide finish blade I believe and the coating seemed to start to turn the cotton ball VERY black...
Just a thought... !

 

OR @CoolBreeze135 Could said black oxide be physically removed from the cutting portion?? What would it take or I guess how deep could the treatment be?? Would a light scrubbing with steel wool of the finest dang sand paper you can find do the job. SOS pad?? Magic Eraser? Yes you would obviously loose the logo but that is not the point.
I believe you could easily protect the cutting edge and use one of those methods..

 

I personally would like to see the un-coated Camp Lore blades remain in the lineup. I feel the CR2.5/JG3/RB3 are the perfect size for skinning and processing meat/fish.


I would love to see TKC make G10 scales for the JG3... Orange would be a nice choice for a dedicated hunting/fishing blade.

 

I’m pretty sure the stone wash camplore blades have been phased out in favor of the black oxide.

 

people have been using bone/antler/leather and wood handles for thousands of years with no issues.......and they ALL absorb blood and fluids......

and for thousands of years there was no plastic cutting boards or bleach , people just rinsed their wood surfaces with water and wiped their blood stained knives down, with no issues.

not sure micarta is really an issue for food prep.

 

There was a YouTube video I commented on, I think it was coalcracker bushcraft. He was showing how he washes his pots and pans in the field. Of course the trolls had a field day citing FDA regulations and bla bla bla. I said similar things. Look at cast iron. Technically you don’t wash them with soap or bleach etc. you just wipe them out and use them again. No issues. If you take a paper towel and wipe even a clean one you’ll get a black residue. No big deal. I use old hickory butcher knives and a wooden butcher block. Yea they are oiled but blood still soaks in yet again no issue. The list can go on and on. The big thing is the limited amount of exposure. Unless they were dipped in liquid mercury and some of that got in your potatoes then you should be fine. Now I do agree that maybe some nice G-10 grips would be nice I won’t lose sleep over it. I will still use my knives for everything without worry. After all when the bus or semi run me over they won’t care about the coating on my knife....

 

I should also say that if you are concerned find a different knife for food prep. Nothing wrong with an extra knife in the pack. The problem with this topic is unless you do millions of dollars of testing you’ll never have a defining answer. After all everything in science is just theory. Nothing is ever technically proven as law, it just hasn’t been proved wrong... yet...

 

I completely see what you are saying. That is why I said from what I understand. In a ideal situation like a kitchen would I slice up some chicken on my cutting board with a micarta handled knife then dry it and then slice up the fresh veggies for dinner? Heck no! If you have a safer option why not take it. . Same goes with the black oxide. If it is potentially dangerous there are other good options