Weird patina problem

M

mdsmith

Joined
Jan 7, 2009
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Well, I guess it's the patina. Every time I use my chestnut swayback to cut something like fruit, it gets this weird blue stuff on it that almost looks like ink. It actually comes off on whatever is being cut. I have other carbon knives that have nice patinas on them, but never saw anything like this. I washed the blade with warm soapy water, but it still seems to happen. Anyone else experience this? I assume it's something on the blade, but what is the best way to remove it?
 
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Is there already a patina on the blade, or is it still shiny and polished? Either way I suspect it has to do with the high polish of the blade (at least when you first got it). Rust and corrosion likes to find little nooks and crannies to form in. The rougher the blade, the more prone it is to corrosion, and the harder it is to get rid of. A mirror polished blade like that on the SBJ might get corrosion, but simply wipe away since there's very little for it to grab onto.
 
It has a patina on it. Nothing really dark, but the blade is no longer shiney. It is a light grey, with the normal blueish undertones. But the stuff I'm talking about actually looks like blue ink. I'll slice up a bananna, and there will be the ink like spots on the blade, which do wipe off, and it will also be on the bananna. Pretty weird, huh?
 
I've experienced a similar blackish residue while cutting apples with a few of my carbon steel blades. Others, never seemed to have the problem.
The big difference that I can see would be the level of patina. The ones with less, or a thinner layer, are the ones that have the reaction. It's as if the fruit is interacting with the metal, under that patina, and cleaning off the exposed metal. Weird question, do those blades have a metalic smell to them, especially when cutting fruits? Mine do. The answer might be adding more patina, and oiling the blade after use.
The best patina I have ended up in mutliple layers, adding oil after each cleaning. It is "thick" and slick, with no odor or colors, that I can see or smell.
Good luck, and maybe someone else will have some more insight.
 
That does sound kinda weird.Could it be a soap residue that has dried?Or do you polish it after the soap wash?Something is obviously there on the blade if if come off on fruit.Ive never seen a regular patina do that although many times it will have a nice blue hue to it.I like shiny myself so i dont have much direct experience.:D
 
That is very interesting. It sounds like the acids in the fruits are reacting with something on the blade; maybe not the blade itself. All the carbon steel knives I have will discolor some when cutting fruit (apples, oranges) but I've never had color come off on the fruit itself. With a brand new blade, I have had a metallic taste the first couple of times I used the knife on fruit, but not after a patina began forming.

I think there must be something on the blade. - Ed J
 
Could it be oil/grease residues from the joint?

You could try cleaning the blade with a scouring pad/Scotchbrite type of thing and giving the blade a matte finish, this tends to enhance even patina. You could also use it more in the kitchen cutting veggies and even meat, this will bring on the patina a treat and hence reduce any staining due to oxidation.
 
This would be very interesting to look at, if you could post a pic or two (of the blade AND the fruit, with the blue stuff on it). Very odd.

A normal 'patina' can be removed by polishing. Don't know if you've tried that, already. But, if not, might use some Simichrome/Flitz to polish the blade thoroughly, then wash it thoroughly afterwards. Try again with the fruit, see if the blue stuff still shows up.
 
My new 2010 chestnut sbj has the terrible metallic odor and even taste (on the apple). It is brand new (2 days) and I am glad to hear that others have had the same experiences. Thanks/
 
all my CV knives to it and some of my other carbon knives do it, never much questioned it, but my case cvs are worse than lets say the 2010 forum moose w/1095
regards
gene
 
I'll run a test on mine tomorrow and post results and photos. I just ate dinner and am not in the mood for an apple right now and it will be too late in the day for me to take the necessary photo documentation later this evening. This is an interesting issue and I don't think I've cut an apple with my SBJ to date although I have used it on other food. - Ed J
 
I have experienced this with other carbon steels. I have a Condor "kephart" that looks like a cross with a kephart and muck design that I use in the Kitchen every day.

The steel is 1075 if I remember correctly. It will do this as well. In fact, just today, I was cutting up some yellow peppers. I put the knife aside for a minute and then sliced some more. dark grey/bluish residue on a slice of pepper!

The knife has a very heavy patina on it. It used to be an almost black finish patina, but I recently dinged the edge on a wire and had to touch up the edge on my belt sander. So I re applied the patina because the edge was all shiny again, so it is not quite as heavy as it was.

I wonder if it has to do with that particular knife having a higher carbon content. Steels will vary a bit even within each steel type category.
 
I have to apologize because I did not get to do the test today as expected. We don't have any apples at home here and I did not get to the grocery store to pick any up, so maybe tomorrow. Sorry guys. - Ed J
 
i've never experienced anything like that with my carbon steel kitchen knives and i cut lemons, tomato's, onion's ,etc (both san mai construction and full carbon). my carbon steel kitchen knives are not the same steel as your chessnut, maybe thats what's going on :confused:.
 
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Could be the steel content yes. However, I'm wondering if the knife having brass liners plays any role here? Brass 'bleeds' and will create verdigris, perhaps it gasses and reacts with the carbon blade. But then, I'm no metallurgist.
 
Finally, I have had an opportunity to do the little test I spoke about earlier in the thread. The materials used - one Case Chestnut bone CV swayback jack lightly used and one golden delicious apple (all I had available). The first picture below is the mark side of the knife before the test. Unfortunately, I didn't have the foresight to photograph the other side. More about that later. Here is the knife before the apple adventure:

knives1104-009.jpg


I rinsed the knife and the apple before I began the experiment. This next photo is the knife and half of the apple after the first cut:

knives1104-010.jpg


I cut the apple in six wedges and ate each wedge as it was cut and prepared. The next picture is a photo of the last cut on the apple.

knives1104-012.jpg


At this point the test had basically been completed and I went to the water hose and rinsed the apple juice and fiber off the knife. These two pictures are of the blade after the test, both sides. There is more tarnish patina on the pile side of the blade because the juices ran around the blade when it was sitting on the plate while I ate the previous slice. Unfortunately I did not get a "before" picture of that side. Anyway, here is the "after" photos which are not different from what I expected to see:

knives1104-014.jpg


back side:

knives1104-015.jpg


Notice that I did not get any "black spots" on the blade or any discoloration on the fruit, nor any metallic taste in the apple either.

This is not definitive, just a data point.

Ed J
 
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TLARbb said:
Finally, I have had an opportunity to do the little test I spoke about earlier in the thread. The materials used - one Case Chestnut bone CV swayback jack lightly used and one golden delicious apple (all I had available). The first picture below is the mark side of the knife before the test. Unfortunately, I didn't have the foresight to photograph the other side. More about that later. Here is the knife before the apple adventure:

knives1104-009.jpg




I rinsed the knife and the apple before I began the experiment. This next photo is the knife and half of the apple after the first cut:

knives1104-010.jpg


I cut the apple in six wedges and ate each wedge as it was cut and prepared. The next picture is a photo of the last cut on the apple.

knives1104-012.jpg


At this point the test had basically been completed and I went to the water hose and rinsed the apple juice and fiber off the knife. These two pictures are of the blade after the test, both sides. There is more tarnish patina on the pile side of the blade because the juices ran around the blade when it was sitting on the plate while I ate the previous slice. Unfortunately I did not get a "before" picture of that side. Anyway, here is the "after" photos which are not different from what I expected to see:

knives1104-014.jpg


back side:

knives1104-015.jpg


Notice that I did not get any "black spots" on the blade or any discoloration on the fruit, nor any metallic taste in the apple either.

This is not definitive, just a data point.

Ed J
Click to expand...

Looks like you've got the beginning of a really nice patina on that swayback. I have one too; now I'll have to go 'speramint a bit !! :D
 
Best money I ever spent on a pocketknife. The apple wasn't particularly good - too hard and not much taste. Ed J
 
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