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Carbon knives rust v. patina

wjschmitz Dec 27, 2010 11:11 AM

I just ordered my first carbon steel (non-stainlesss) knife: a Misono Swedish Steel 240 mm gyuto. And, even though it hasn't arrived yet, the more I read, the more worried I am getting about caring for this knife.

Does anyone have advice for developing a nice patina on a carbon knife to deter it from rusting? I am very careful with my kitchen tools, and always wash and dry my knives by hand, shortly after use. But it sounds like this may not be enough.

Should I try to force the patina? i.e. soak in vinegar? Or let it develop naturally?


PS I have a nice set of Japanese water stones, and am gradually getting better at sharpening my knives, so hopefully that won't be an issue.

  1. PBSF Dec 27, 2010 12:23 PM

    As long as the blade is wiped dry, it will not rust. Acid food will cause the blade to darken but that is not harmful in any way. I use mostly carbon steel knives and rust has never been a problem.

    1. scubadoo97 Dec 27, 2010 12:42 PM

      Just wash and dry it promptly after use. I live in humid Florida and my knives are out in the open with no protectors on them. I have not had any rust issues with my carbons unless I have forgotten to wash and dry them directly after use. You only need to do that once. Patina will form naturally with use.

      1. Chemicalkinetics Dec 27, 2010 12:43 PM

        Hey Bill,

        I don't have this knife, so I cannot say for sure. I have a few carbon steel knives and they behave differently. My Tanaka Kurouchi nakiri is made with aogami (blue paper) carbon steel and it is mildly resistance against oxidization. It develops a nice bluish patina layer. Very pretty. I just let it develops its own patina. My CCK Chinese chef's knife is made with an unknown carbon steel. It can form patina or rust depending the situations. If I leave too much water, it will develop red rust. If I keep the knife dry, it will develop a bluish or greyish patina. Once it depends a good layer of patina, then it will not develop red rust, so I only have to be very careful the first few days after knife sharpening when the knife blade is fresh. If red rust appears, then I just use Bar Keeper's Friend to remove it. Here is a photo which I hope to demonstrate the faint blue patina.

        My Tojiro usuba, on the other hand, is made with shirogami (white paper carbon steel) and it is very easy to develop red rust. Again, if a thin layer of red rust is develop, I use Bar Keeper's Friend to remove it. If the layer is thick, then I may grind it out using sharpening stones. I don't force patina on my knvies. I hope this help.

        7 Replies
        1. re: Chemicalkinetics
          cowboyardee Dec 27, 2010 06:53 PM

          +1. I prefer letting patina form naturally too.

          That said, a forced patina, if the OP is interested, can be more uniform. It will also tend to be more red than a natural patina (this is still not rust, assuming you force a patina carefully), but that depends in part on the knife.

          Also to the OP - sharpening won't be an issue, but note that sharpening will remove the patina from the edge of a knife. This is inevitable, and you should not be concerned.

          1. re: cowboyardee
            kaleokahu Dec 27, 2010 07:11 PM

            cowboy: I know you know your way around knifemaking, so I have to ask: Have you tried etching any blades in dilute printed-circuit board acid? The reason I ask is that I've used this acid to bring out temper lines in oil-quenched blades, and I think it forces a really nice, uniform grey patina not unlike a very fine beadblast finish. I use it 50/50 with distilled water, and then after, a good stir in some baking-sodawater to neutralize.

            1. re: kaleokahu
              cannibal Dec 27, 2010 07:18 PM

              ferric chloride(FeCl3) is the stuff you refer to, just made a batch of PCB's an hour ago :)

              i'll have to give this a try next time i'm coaxing patina out of carbon. sounds interesting for sure.

              edit: for anyone going this route, make sure to clean the knife off very well afterwards. ferric chloride is nasty stuff and the last place you want it to end up is your mouth.

              1. re: cannibal
                Chemicalkinetics Dec 27, 2010 07:30 PM

                That is ok. Ask your demon pig to take care of it.

                1. re: Chemicalkinetics
                  cannibal Dec 27, 2010 07:37 PM

                  haha yes, it will do my bidding! maybe i can get it to sharpen my knives too :P

              2. re: kaleokahu
                cowboyardee Dec 27, 2010 07:31 PM

                I have not tried it. Sounds interesting though. 30something % hydrochloric acid (before mixing with distilled water)? Do you soak or just wipe on and off? What steel[s] were you working with?

                Might give it a try next time I thin the massive primary bevels on my nakiri or yanagi.

                Truthfully, I'm not sure why some acids or methods seem to create more reddish hues than others. Like most good knife nerds, I prefer bluer patinas. I wonder if us knife guys could learn a thing or two from gun nuts who have been deliberately 'bluing' their guns for years, but I haven't gotten around to investigating too much. At any rate, there's something more romantic (in my mind anyway) about 'earning' a patina through use.

                1. re: cowboyardee
                  kaleokahu Dec 27, 2010 08:18 PM

                  cowboy: It's Bob Kramer's recipe, 50/50 ferric chloride (Radio Shack!) and water. Strictly wipe on for a few seconds (but I've also double-dipped with no trouble). The only steel I've done it much with is 52100.

                  This was definitely not red. I've fooled with the "instant bluing" paint-ons some, too, without much success. Just from reading the Brownell's "Gunsmithing Tricks" books, I gather you pretty much have to have a hot tank setup to lay down much real bluing--hard on your handlewood and escutcheons. Maybe the French Grey is different, I dunno.

                  I get you about the earned patina. Then again, there's a romance all its own about "earning" your way through the bluing on a good gun.

          2. w
            wjschmitz Dec 27, 2010 01:35 PM

            Thanks to all. I was starting to second guess my decision. Now I am anxious for the UPS truck to arrive!


            1. l
              la2tokyo Dec 27, 2010 04:36 PM

              Whatever you do, don't soak it in vinegar.

              13 Replies
              1. re: la2tokyo
                Chemicalkinetics Dec 27, 2010 04:42 PM

                Not that I forced-patina my knives, but vinegar is used for forced-patina.

                1. re: Chemicalkinetics
                  scubadoo97 Dec 27, 2010 05:22 PM

                  and mustard ;)

                  1. re: Chemicalkinetics
                    cannibal Dec 27, 2010 06:15 PM

                    and soda ;)

                    1. re: cannibal
                      Chemicalkinetics Dec 27, 2010 06:26 PM

                      I know about mustard, but I didn't know about soda. :)

                      1. re: Chemicalkinetics
                        la2tokyo Dec 27, 2010 10:49 PM

                        Really?!?! I just googled forced patina and I'm shocked that anyone would actually do that! It doesn't really make sense to me.

                        I have a Masamoto gyuto that my roommate cut lemons with when he was making cocktails one night. He didn't wipe it off, it sat for three days, and there's a bunch of deep pits in it where orange pools of rust formed. It's still usable but it's much more difficult to keep clean and dry now. IMHO the pits definitely do not add to its appearance.

                        1. re: la2tokyo
                          scubadoo97 Dec 28, 2010 04:34 AM

                          mmmm. I don't think anyone is advocating a 3 day soak to force a patina. Do you still have this roommate?

                          I don't routinely force a patina on my knives but did try it a couple of time. Not worth the effort but you can do interesting things to get wavy lines and designs on you blade.

                          1. re: la2tokyo
                            Chemicalkinetics Dec 28, 2010 06:41 AM


                            In the situation you described (lemon juice stay on the blade in an open air environment), it favors red oxide (red rust) formation over black oxide (patina). I won't be surprised those are rust spots on your Masamoto.... When you scratch those pit areas with your fingernail, do they feel like smooth or rough? Because those are probably not patina, you probably should remove them.

                            As for your question regarding why people like patina. Here is what I think. Carbon steel can turn into red rust or form a patina surface. Once a patina surface is formed, then it is difficult for the red rust to take over. As such, patina is like a protector against red rust -- that is the true practical reason. Since the goal is to form patina over red rust, one can achieve this by daily use and daily care, or one can force the patina on.

                      2. re: Chemicalkinetics
                        benjamin23 Dec 29, 2011 05:24 PM

                        I bought a CCK cleaver a while back, and after removing the lacquer I decided to allow it to develop a patina naturally. I was pretty diligent about keeping it dry, but nevertheless it developed some rather ugly red rust. Last night I decided to experiment and soaked a paper towel in regular white vinegar and left it wrapped about the edge of the blade. After an hour or two the rust had disappeared and was replaced with a fairly nice bluish patina. I replaced the vinegar and towel once during the process. I'm quite pleased with it now, so I'm inclined to advocate vinegar for forming patina. Mustard would probably be just as good, as it would sit more uniformly than ordinary vinegar without using a towel.

                        1. re: benjamin23
                          Chemicalkinetics Dec 29, 2011 05:40 PM

                          "Last night I decided to experiment and soaked a paper towel in regular white vinegar and left it wrapped about the edge of the blade. After an hour or two the rust had disappeared and was replaced with a fairly nice bluish patina. "

                          Awesome. I didn't use a lacquer removal, but I thinned the lower 1/3rd of the blade, so that part has lost its lacquer.

                          In my case, I would try to keep the blade clean and dry and if it has any hint of forming the red rust, then I remove it using Bar Keeper Friend. Now, it is has this bluish shiny rainbow color. Very nice. :)

                          Your method seems to be much more direct. This is cool.

                          1. re: Chemicalkinetics
                            BiscuitBoy Dec 30, 2011 06:12 AM

                            Chem - Are thinning on a grinding wheel or by hand with a stone?

                            1. re: BiscuitBoy
                              Chemicalkinetics Dec 30, 2011 08:10 AM

                              Just by hand on a few stones -- not really trying to remove a lot of metals.

                              1. re: Chemicalkinetics
                                BiscuitBoy Dec 30, 2011 08:17 AM

                                what grit for thinning?

                                1. re: BiscuitBoy
                                  Chemicalkinetics Dec 30, 2011 08:46 AM

                                  You have a CCK knife, right? I was merely trying to grind out all the original grind mark at the lower 1/3rd (or 1/4th) of the knife blade. To be honest, I think I started off with DMT coarse stone, not XC, then quickly onto Bester 1000 grit, and ....

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