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I Forge Iron

Kitchen knife issues


Hayden H.

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So I made my mother a new kitchen knife for Christmas out of a coiled suspension spring I got from a car junkyard. I made one knife from it before and it has been good so far. No issues with the steel. But with this kitchen knife it seems to be having issues with food. She used it last night to cut onions and when I looked at it just to check and make sure nothing tried to rust or anything I found this brown staining and I have no clue what it is and was wondering if there was some way to prevent this or if I just used a bad steel for this sort of project. 

 

(Before and after of the knife. I’m still not very good at knife making so it doesn’t exactly look professional.) 

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On 12/29/2018 at 6:10 PM, sfeile said:

Food acids will color carbon steel. As long as the blade is being washed and dried properly after use so that it is not rusting, the patina is normal.

I figured it had something to do with that but wasn’t 100% certain so thank you for the info. 

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In fact - you WANT patina. It's an oxidation layer that helps prottect against the "bad" oxidation - the red one. Patina will evolve on it's own over time, and is also caused by some types of food like onion, garlic and mustard. I like to accelerate patina by rubbing my blades with cut onion or mustard.

Clean your knife with soft material to keep the patina.

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Another thing to keep in mind with blades that will be used in food processing (and there have been some lively discussions on here regarding this topic) is that pitting and imperfections on the surface of the blade can trap bacteria which can then get passed to food and then people. In general you want that surface to be defect free with a fairly high grit finish.

I'm not typing any of that to discourage you.  I just want to make sure you are aware of the situation.  Good on you for forging out a usable knife.  I'm looking forward to seeing more from you in the future.

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I have a 1956 kabar kitchen knife; the entire blade has a nice brown patina to it. (Was my Mother's 2nd wedding anniversary present.)

Carbon steel blades can also transfer a bit of off taste when used for certain jobs---which is why they used to make silver bladed fruit knives!

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