# Applying Cold Blue to kitchen knives



## KnightKnightForever (Sep 13, 2021)

I've read mixed reviews on the food-safety aspect of applying cold blue to kitchen knives, but I watched a scientific video that broke it down and I feel comfortable enough now not to worry about it. I'm waiting for a customized denka no hoto to come shipped from FT, and I have a new handle I want to put on and then I want to cold blue the carbon steel to make it more rust resistant (and I think darkening the blade will look awesome too). Anyone have some before and afters of their own experiences?


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## HumbleHomeCook (Sep 13, 2021)

I've cold blued enough gun parts that I wouldn't do a blade. Maybe it works out alright but it isn't very robust. Cold bluing is generally for small stuff.

Also, if it isn't smooth in the end, I most definitely wouldn't do it. My experience with many "dark" type blade finishes is they drag.


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## Dull_Apex (Sep 14, 2021)

Have you seen posts about instant coffee patina? The process is basically leave the edge in super concentrated instant coffee to darken the core, and doesn't have a risk of non-foodsafe chemical contact.


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## btbyrd (Sep 14, 2021)

For the love of God, don't blue a Denka's core steel. Just use the freaking knife and it'll patina and be fine in a week.


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## tostadas (Sep 14, 2021)

You can darken the core with simple non-toxic acids. I've used lemon juice, hot vinegar, and instant coffee, all with good results.

Here's one I did on a TF with hot vinegar and instant coffee, before and after










Here's a Kono FM with lemon juice applied for a couple minutes at a time, buffed off with some natural stone mud in between.


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## M1k3 (Sep 15, 2021)

Hot Balsamic vinegar etch!


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## Jovidah (Sep 15, 2021)

My first response: just force a patina. Gets you most of the way there without the fuss.
My second response: if you're this worried about rust resistance, get something (semi)stainless instead.


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## KnightKnightForever (Sep 15, 2021)

All good advice. Thanks


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## Rotivator (Sep 15, 2021)

KnightKnightForever said:


> All good advice. Thanks


I have been playing with equal parts by weight vinegar and wheat flour. Looks like 3 hours is a good length, and gives the ability to control exactly where you apply patina. Hoping to post results in the next week or so. 

I've also done mixed patina with mustard and coffee. Pretty cool results


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