Phosphoric acid

[Natlek]

Well , friend of me have auto body shop and he give to me this bottle with phosphoric acid ..I try it on steel and it works ...fast .Oxide layer seems to be very durable and constant color .Plus I can watch how things go on and I can stop whenever I think that I have good color .....It is more durable then what I get with vinegar without any doubt .I like it and I will use it ...but . I know that this acid was added to some food ,drinks.... BUT what about this oxide layer on steel ? Question is , is it SAFE for use knife on food with this ?
On label of this bottle is written that it is rust removal and for rust protection .....Anybody try this treatment on blade ?

 

[navman]

Makes sense to me. Essentially you Parkerized the steel, a process that has been used for decades in the firearms industry..

https://en.wikipedia.org/wiki/Parkerizing

 

[Natlek]

Thanks for that link ..........

A stream of small bubbles is emitted from the metal part as the process takes place; when the bubbling stops, the process is complete

Then what is the catch ? I try to search here but found almost nothing ..........?

 

[navman]

Not sure. Other than old school military bayonets and trench knives I haven't seen many parkerized knives, but looks like a good process for high carbon, non-stainless user blades. The finish is durable on the 1911's I have that are parkerized.

 

[DanH45]

I believe parkerizing is safe for food use blades.

 

[Lieblad]

As far as ”food safe. Phosphated finish in itself is fine. I would never worry about using such a foodprep knife
But on a microscopic level, its a rough surface what can better carry bacteria. But, Thats no different than Old Hickorys or orher patina carbonsteel blades.
Just be reasonably sanitary like you would with any other knife using for food prep.