Are acid washed knives safe for food prep?

[carpdiem]

I was thinking about doing either a vinegar or ferric chloride acid wash on my cpm m4 mule to prevent uncontrolled corrosion, and making it basically a permanent kitchen knife, but it got me wondering about the safety of the coating left on the blade.

Does anyone know what, chemically speaking, that coating actually is, how easy it might be to rub it off (say, cutting through something tough, like squash), and whether or not it is food safe if rubbed off?

[JRinFL]

Good question. At first I thought it was an easy answer, but on reflection I had to admit that I don’t know. There might be some chemical reaction that could possibly be harmful, but have little idea. Hopefully someone with a chemistry background will see this and post.

[RustyIron]

Vinegar is in the dressing you put on your salad.

Ferric chloride is used to treat the water used to make your Kool-Aid.

Your stainless kitchen knives are 1/6 chromium. Chromium? Remember the movie Erin Brockovich? It will destroy your kidneys and liver, in addition to creating those unsightly skin ulcers. Believe it or not, it's BETTER to cut your food with a coated blade.

[Granoo Fink]

Short version: an aqueous solution of Ferric Chloride creates an environment in which the components of the steel can be oxidized.
The results are Oxide layers of various thickness, therefore the different colors.
The Oxide layers of "stainless steel" consist of a thin (only a few atomic layers) cover of Chromium Oxide, which strongly adheres on the surface.
By contrast, the artificially induced Oxide layers consist of Oxides of all components of which the metal ions can be released in much greater amounts.
I would never use a blade with acid wash for food prep.

[JRinFL]

Short version: an aqueous solution of Ferric Chloride creates an environment in which the components of the steel can be oxidized.
The results are Oxide layers of various thickness, therefore the different colors.
The Oxide layers of "stainless steel" consist of a thin (only a few atomic layers) cover of Chromium Oxide, which strongly adheres on the surface.
By contrast, the artificially induced Oxide layers consist of Oxides of all components of which the metal ions can be released in much greater amounts.
I would never use a blade with acid wash for food prep.

Thank you!

[RustyIron]

I would never use a blade with acid wash for food prep.

Why?

[Granoo Fink]

I would never use a blade with acid wash for food prep.

Why?

Thank you for the question.

Admittedly, this is a simplification.
One has to differentiate between the guy who knows what he does and the other one.

There are some parameters to pay attention to, like concentration of Ferric Chloride or time and what else. You can use electrical current to speed up or to slow down the reaction, only to give an example.

I'm not into the subject, so I don't know what else becomes important here. But if you're doing it wrong, your blade will end up ruined with unevenness and/or bleeding Oxide spots. If your artificial Oxide layer is porous because it has grown too fast, it may flake off or acidic foods could leech out metal ions.

For example, Dawson Knives does something they call Arizona Copper Finish. I'd guess this is some kind of electrochemical treatment. And they put a clear Cerakote coating on their blades.

[carpdiem]

Short version: an aqueous solution of Ferric Chloride creates an environment in which the components of the steel can be oxidized.
The results are Oxide layers of various thickness, therefore the different colors.
The Oxide layers of "stainless steel" consist of a thin (only a few atomic layers) cover of Chromium Oxide, which strongly adheres on the surface.
By contrast, the artificially induced Oxide layers consist of Oxides of all components of which the metal ions can be released in much greater amounts.
I would never use a blade with acid wash for food prep.

Thanks!

Do you know if the acid washes by vinegar or other methods produce an oxide layer more similar to the "natural", though, oxide layer?

I know many Japanese chef knives are carbon steel and must produce some kind of oxide layer (and presumably they're food safe!), and I'm interested in doing something to help protect the surface of the m4 mule from active pitting and rust as I'd love to use it for food prep, but I expect the knife won't get babied by everyone in my household.

[Granoo Fink]

I don't know much about M4. The difference to low alloy steels like shiro-ko is, that low alloy steels do not contain chromium or other alloying elements in noteworthy amounts. The Kurouchi finish (black forged) is one of these methods, but without care, they will rust anyway.
Treatment with "softer" methods are more suitable for knives for food prep. Mustard, vinegar or onions are working much more slowly than Ferric Chloride, thus they are less prone to "overreacting". But any kind of chemical treatment will produce disorder in the atomic lattice and this is the starting point for pitting. Said, you can extend the time after you have to care, but you have to care.
Another method to lower the tendency to corrosion is to polish the steel which reduces the raw number of points that can be chemically attacked. At least, your Hap40 Sukenari will rust, too, if you don't care.

[Superflex]

Vinegar is in the dressing you put on your salad.

Ferric chloride is used to treat the water used to make your Kool-Aid.

Your stainless kitchen knives are 1/6 chromium. Chromium? Remember the movie Erin Brockovich? It will destroy your kidneys and liver, in addition to creating those unsightly skin ulcers. Believe it or not, it's BETTER to cut your food with a coated blade.

Me thinks you should understand the difference between hexavalent chromium, trivalent chromium and chromium carbides. :)

[Eliteone2383]

Vinegar is in the dressing you put on your salad.

Ferric chloride is used to treat the water used to make your Kool-Aid.

Your stainless kitchen knives are 1/6 chromium. Chromium? Remember the movie Erin Brockovich? It will destroy your kidneys and liver, in addition to creating those unsightly skin ulcers. Believe it or not, it's BETTER to cut your food with a coated blade.

Me thinks you should understand the difference between hexavalent chromium, trivalent chromium and chromium carbides. :)

Came here to post this.

[standy99]

viewtopic.php?t=73637

Acid etched blades account for nearly every Japanese chef knife you have ever seen.

Acid causes a reaction but doesn’t stay on the non porous blade.

[Sonorum]

viewtopic.php?t=73637

Acid etched blades account for nearly every Japanese chef knife you have ever seen.

Acid causes a reaction but doesn’t stay on the non porous blade.

I don't know enough about this to make an absolute statement guising someone in their decision but this makes sense to me, personally. What difference is there between a knife with a forced oxidation and and non stainless kitchen knife developing patina? And I mean that partly rhetorical and partly legit question.

Calling professor Larrin, hello?

[Granoo Fink]

viewtopic.php?t=73637

Acid etched blades account for nearly every Japanese chef knife you have ever seen.

Acid causes a reaction but doesn’t stay on the non porous blade.

I don't know enough about this to make an absolute statement guising someone in their decision but this makes sense to me, personally. What difference is there between a knife with a forced oxidation and and non stainless kitchen knife developing patina? And I mean that partly rhetorical and partly legit question.

Calling professor Larrin, hello?

The reaction rate.

[RustyIron]

Me thinks you should understand the difference between hexavalent chromium, trivalent chromium and chromium carbides. :)

Uhhh... yeah.
I thought the absurdity of the implication was side-splittingly funny.
Sometimes I really crack myself up.

Incidentally, this morning I had a sliver of steel stuck in my hand, and my friend used my K390 blade to cut it out. Hope the blade doesn't pose a health hazard.

P.S.
That's a joke too. It didn't even occur to me to wash our hands, and we weren't even wearing masks! But riding with a sliver of steel stabbing my nerve endings with every bump would have been a total bummer.

[z4vdBt]

How is DLC for food prep?

[Sonorum]

viewtopic.php?t=73637

Acid etched blades account for nearly every Japanese chef knife you have ever seen.

Acid causes a reaction but doesn’t stay on the non porous blade.

I don't know enough about this to make an absolute statement guising someone in their decision but this makes sense to me, personally. What difference is there between a knife with a forced oxidation and and non stainless kitchen knife developing patina? And I mean that partly rhetorical and partly legit question.

Calling professor Larrin, hello?

The reaction rate.

Sure, but how does that affect the safety of using the steel?

[dsvirsky]

Sure, but how does that affect the safety of using the steel?

It doesn't. Y'all are over thinking this.

[Sonorum]

Sure, but how does that affect the safety of using the steel?

It doesn't. Y'all are over thinking this.

That's what I'm trying to get at.

[Stuart Ackerman]

Like I said before elsewhere in this forum..we are begining to overthink everything.

When you sharpen an edge, you are exposing the same structure that etching does.
Anyone died yet from that exposure?

Once the etching is done, a netraulising agent is used to stop the etching.

There is nothing left behind to harm you.