Does the darkness and/or cause of a patina change its effectiveness?

S

SCWillson

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Aug 2, 2013
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Thought I'd ask this of the "old school" steel experts.

Is a dark patina better at rust prevention on a carbon steel blade than a lighter-colored one? What about multi-colored patinas such as caused by cutting certain foods such as mangos? Does any of that matter, or is it simply that it has any patina that makes the difference in rust prevention?

I only own (thus far) one traditional slipjoint, a Northfield #92 Talon. Since I got it a few weeks ago it has acquired a light patina with a few darker streaks from cutting bananas and apples. I like the way it looks now but wonder if I should try to get it darker. And of course as I get new traditionals I want to do right by them as well. (I should perhaps mention all my knives are users; I don't do safe queens.)
 
My advice is don't overthink it. If it's intended to be a user, then sharpen it and use it. An honest patina takes time.
 
I'm fine with an "honest patina"; I'd just like to know if a patina needs to reach a certain point before it becomes effective. If any level of patina prevents rust then it's all good. :)

I've seen all sorts of patinas on these boards; the first time I'd ever even heard of GEC was on a thread here at BF with a picture of an almost-black-bladed wharnecliffe #72. It looked pretty cool, but I've come to appreciate the subtle beauty of the more "organic" patinas.
 
Used everyday, the patina will darken over time by itself. I have no scientific evidence, but I think a patina helps a bit. The old guys I knew when I was a kid would stick a new knife in a potato overnight to start the patina. Here is a Northwoods I've had since April, and it's been an everyday user. The patina is a bit spotty, but on the other hand, this knife has been exposed to salt water and a salty environment on the Chesepeake Bay here in Maryland. It's also been dunked in the Potomac river to rinse off the fish guts or chicken liver slime when cat fishing. No rust so far, in spite of being 1095 carbon.

Living in west Texas you're in a pretty dry climate. I'd just wipe it down everyday with a clean dry bandana and let the patina continue to build. I figure it can't hurt, but it may help. Patina is just a top layer of oxidized metal, like the old brown finish on muskets. But keep in mind that the patina keeps on changing. The spotty pattern will change as you cut stuff, so it's kind of interesting. I shared a large hot dog with sauerkraut with my better half, and after cutting it in half, I set the knife down to eat. The acid in the sauerkraut made new splotches. The next day my better half and I were out on a lake in the canoe, and pulled up on a shady bank for lunch. Some tomato and mozzarella cheese was sliced up to go in a pita, and the knife was set down on a log while we ate. Again, the patina was a slightly different pattern on the blade. But it was a bit darker. It got rinsed off in the lake and wiped down with a bandana, and dropped back in pocket. It's going to be interesting to see how the patina keeps going. I'll post more pics as it happens.

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Beautiful Northwoods stockman there, and the patina on those blades are exactly the kind of "organic" (as in self-creating from use) that I like best.

The patina on my #92 is still quite light; I think my darkest areas are only as dark as the lightest areas on yours. But the knife is still pretty new, so it should improve with age...
 
SCWillson said:
Beautiful Northwoods stockman there, and the patina on those blades are exactly the kind of "organic" (as in self-creating from use) that I like best.

The patina on my #92 is still quite light; I think my darkest areas are only as dark as the lightest areas on yours. But the knife is still pretty new, so it should improve with age...
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Oh yeah, it will continue to darken to a deeper gray. It may be a bit splotchy, but that's natural if you are really using the knife. This GEC number 15 was also used under salt water conditions, and a bit of rust spotting got on the steel liners. The blade was not rusting. The rust spots came right off with a little rubbing with 3-In-1 oil on a pipe cleaner. Left some dark pepper spots, but that doesn't affect anything.
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Main thing is, just use the heck out of the knife, and look it over that night for any rust. Wipe off as needed, a swipe or two on a stone for the edge, and you'll be good to go. The blade will darken in time to it's own patina that will be unique from your own use on it. :thumbup:
 
Got it.

You know, I've seen lots of stuff regarding patinas on blades, but doesn't anyone patina their backsprings and other carbon steel parts? Seems to me those would be plenty susceptible to rust.
 
I don't patina my backsprings I've noticed the butt darkens first, then the part near the pivot then everything else eventually. I'll oil the back spring when I oil the blade with whatever's left over on my fingers. If any rust spots appear, rub it with some paper and then oil it. It'll be abrasive enough to get any little rust spots out and will get darker. If it's been neglected for a bit, maybe use something like a rust-erasor.
 
I use this 194OT pretty regularly to cut food and fruit and it's developing a nice patina.

194OTBuckle_zps41ba9dac.jpg
 
Some really 'dark' patina may not be tightly-bound to the steel. I've noticed much of the deep black patina left immediately after inducing it with vinegar will be easily scrubbed off with baking soda, when cleaning the blade afterward. The grey patina that's left in place is the harder stuff, and is what's doing the real work in resisting additional oxidation (rusting) down the road.

I've also read (in highly technical research docs that I didn't fully comprehend ;)) that the different acids or other caustics used in oxidizing metals will create different colors of oxide, based at least in part on the specific pH of the solution used, and the specific chemical reactions taking place. I'd assume the protective qualities of the oxide will also vary widely by the same reasoning.


David
 
This is from a few months of use. Mangos give a nice dark patina. I don't count on the patina protecting the steel from rust, I oil all my knives once a month.

Regards

Robin
 
I don't count solely on the patina either; I use a touch of oil myself. But the patina looks great on a traditional knife and doesn't get wiped off all the time.

BTW, I love the way that TC barlow looks like it could actually be an antique. Beautiful!
 
SCWillson said:
I don't count solely on the patina either; I use a touch of oil myself. But the patina looks great on a traditional knife and doesn't get wiped off all the time.

BTW, I love the way that TC barlow looks like it could actually be an antique. Beautiful!
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Patina doesn't stay dark where the blade is working. Notice the tip of mine where I cut heavy leather.

Regards

Robin
 
The effect of patina is to make the blade change colors. It is not a rust prevention technique. The only way it helps in rust prevention is that it slightly dulls the surface of a shiny steel knife, allowing oil to adhere to the surface better and longer. I am no steel expert but I have read enough threads where genuine steel experts explained it in great detail to where I believe them. If it prevented rust, no one would have gone to the trouble of inventing stainless steel, they would have just sold carbon steel as "potato treated, never rusts!"

I usually keep my carbon blades polished and occasionally oiled. If a patina develops during normal use I don't fret about it, I know how to remove them if I want to.

I just purchased a used GEC knife that the previous owner had allowed a natural patina to begin to form. Under that black patina the blade had started minor pitting. I cleaned it up and oiled it and it's fine, but those small pits remain. So don't think a patina is some magic protective shield. It's just a different, less destructive form of oxidation.
 
jc57 said:
The effect of patina is to make the blade change colors. It is not a rust prevention technique. The only way it helps in rust prevention is that it slightly dulls the surface of a shiny steel knife, allowing oil to adhere to the surface better and longer. I am no steel expert but I have read enough threads where genuine steel experts explained it in great detail to where I believe them. If it prevented rust, no one would have gone to the trouble of inventing stainless steel, they would have just sold carbon steel as "potato treated, never rusts!"
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The advantages of stainless would have been enough even if patinas were magical rust-proofing, as patinas and any other surface treatment can wear off.

I usually keep my carbon blades polished and occasionally oiled. If a patina develops during normal use I don't fret about it, I know how to remove them if I want to.

I just purchased a used GEC knife that the previous owner had allowed a natural patina to begin to form. Under that black patina the blade had started minor pitting. I cleaned it up and oiled it and it's fine, but those small pits remain. So don't think a patina is some magic protective shield. It's just a different, less destructive form of oxidation.
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I don't think it's "some magic protective shield" either; it's just a natural rust inhibitor that happens to look nice. It doesn't really matter if it helps because it keeps a thin film of oil on the rougher surface or because it partially preempts regular oxidization (as does bluing). It helps, and it looks nice to many knife owners. Win-win.
 
The stable black oxide (Fe[sub]3[/sub]O[sub]4[/sub]) that forms a patina is also the stuff that resists additional rusting, because the oxidized steel at the surface is no longer as reactive to the things that cause rust (Fe[sub]2[/sub]O[sub]3[/sub]). The previously 'free' iron is already bound up with the oxygen, so it doesn't react further to form rust (with oxygen + water). This is why a patina can & does resist rust. Nothing is bulletproof; even stainless can rust. But a patina is not just for changing the color of the steel, even if some only prefer it for this reason.


David
 
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I don't worry about patina at all.
I clean and oil my non-stainless blades regularly, and so far I have not had any corrosion problems.
If a patina develops no worries, and if not also no worries.
Each knife owner is different, so follow your own inclinations.

Peace.
 
David, I'll take your word for the level of effectiveness. You are one of those whose steel knowledge I have come to rely on when reading your past posts. Frank (knarfeng) may chime in here, I have seen him post his views on this topic before.

From what I have read (I am not a chemist) the amount of rust resistance you get just from the patina itself is very small.

http://en.wikipedia.org/wiki/Bluing_(steel) and some of the MIL-SPEC documents it references, repeat the idea that black oxidation (bluing, patinas) add very little rust resistance alone, but is useful when combined with surface treatments (oil).

http://en.wikipedia.org/wiki/Black_oxide also mentions that it provides "mild corrosion resistance" and that is in reference to industrial applied black oxide coatings, not vinegar or apple-induced patina.

My reason for chiming in is that I see the occasional thread or poster where there is an assumption that forming a patina is equivalent of rust-proofing a knife, and that is a myth that I don't think should be allowed to run unchecked, or at least without opposing points of view in place so that a reader can recognize that it's not a universally accepted fact.

Does it help a little? Apparently. Does it help more when used in conjunction with oil? That seems to be generally accepted.
 
jc57 said:
David, I'll take your word for the level of effectiveness. You are one of those whose steel knowledge I have come to rely on when reading your past posts. Frank (knarfeng) may chime in here, I have seen him post his views on this topic before.

From what I have read (I am not a chemist) the amount of rust resistance you get just from the patina itself is very small.

http://en.wikipedia.org/wiki/Bluing_(steel) and some of the MIL-SPEC documents it references, repeat the idea that black oxidation (bluing, patinas) add very little rust resistance alone, but is useful when combined with surface treatments (oil).

http://en.wikipedia.org/wiki/Black_oxide also mentions that it provides "mild corrosion resistance" and that is in reference to industrial applied black oxide coatings, not vinegar or apple-induced patina.

My reason for chiming in is that I see the occasional thread or poster where there is an assumption that forming a patina is equivalent of rust-proofing a knife, and that is a myth that I don't think should be allowed to run unchecked, or at least without opposing points of view in place so that a reader can recognize that it's not a universally accepted fact.

Does it help a little? Apparently. Does it help more when used in conjunction with oil? That seems to be generally accepted.
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The difference I've noticed, in applying patina to my Schrade 8OT and a Case 6375 Stockman in CV, is the patina has done a great job in resisting the rust-spotting that my blades previously exhibited (I purposely left the spey on the Case stockman as is, no patina, just to provide a reference in the difference between them). As with the infinitely-variable conditions that cause variation in the color of a patina, I also believe the particular environment the blades are exposed to will influence how 'effective' the patina will be. For me, it accomplished what I'd hoped it would. I live in the desert southwest, so my knives aren't as vulnerable most of the time. The spotting that turned up on my blades always came around this time every summer (July-August), during our so-called 'monsoon' season of higher daily humidity levels and occasional downpours. My blades that I carried in-pocket would quickly develop spots under these conditions (in just hours), and I'm seeing this summer that the patinated blades are doing much better (and this season's 'monsoon' has been longer and wetter for us, so far).

And the vast majority of the time, my blades are completely un-oiled. For the sake of the pivots mainly, I apply some form of oil after a thorough washing of the knife (maybe 2-3 times/year), but don't bother adding anything beyond that. When I use the blades for anything even slightly messy, I'll wipe down the blades afterward with Windex. So, the vast majority of the time, the patina is the only thing influencing any resistance to rusting.


David
 
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Yes the spring darkens over time. This is my #55 which just developed naturally. No effort was made to force a patina on it, this is just from carrying and using it.

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