Weird 'patina' on Magnacut

[ptolemy]

Has anyone experienced anything like this? Looks like cloudy patina, not your typical one that you get on carbon steel knives. Any insight to what could have caused it? My thinking it's the onions... but why? magnacut is pretty rust resistant

Any insight would be appriciated!

 

[dehory]

Never seen anything resembling patina with onions on my Bidinger and MSicard MagnaCuts. Who’s the maker of the knife?

 

[ptolemy]

Never seen anything resembling patina with onions on my Bidinger and MSicard MagnaCuts. Who’s the maker of the knife?

I rather keep the marker private for now, because they are very reputable, and this is likely my fault, so I want to figure this out first...

 

[dehory]

I respect your discretion, though I wonder what you could possibly have done “wrong” to cause patina on it — across the four knives I’ve owned, MagnaCut is as stainless as any steel I’ve tried.

 

[ptolemy]

I respect your discretion, though I wonder what you could possibly have done “wrong” to cause patina on it — across the four knives I’ve owned, MagnaCut is as stainless as any steel I’ve tried.

yes, I also have another magnacut and I cut lemons with it and just let it sit overnight and nothing happened... so I def wonder, wtf... it's also sorta cloudy.... which is something I have never seen before!

 

[dehory]

Such a mystery. Does it come off with Flitz/Simichrome?

 

[ehhh]

Sometimes when I cut onions with a polished blade like that it leaves a stubborn cloudy residue that doesn't wash off the first time. Try scratching the cloudy part with your nail. If you can scratch it off, then you probably just need to wash it with a soapy sponge and water again.

 

[ptolemy]

Sometimes when I cut onions with a polished blade like that it leaves a stubborn cloudy residue that doesn't wash off the first time. Try scratching the cloudy part with your nail. If you can scratch it off, then you probably just need to wash it with a soapy sponge and water again.

no, i even used rubber eraser and it didn't do much...
i did use scotch brite and that works but process is very tedious and will make finish obviously different....

 

[dehory]

I don’t know any western makers who use lacquer, but is there any chance it’s some kind of coating on the blade that’s reacting with the onions?

 

[ptolemy]

I don’t know any western makers who use lacquer, but is there any chance it’s some kind of coating on the blade that’s reacting with the onions?

no, no chance, i been talking with the maker, and he would have def mentioned it...

 

[Tekkz]

Very strange. Nothing discolors my MSicard magnacut even if I leave lime juice on it.

 

[jedy617]

Magnacut isn't rust proof. It's very stainless but you can still get stains of course...I have stains that look similar on my s90v. That being said magnacut is still quite a bit more stainless than s90v though. My magnacut in the kitchen has no stains at all through.

What was the longest you let it sit before cleaning?

 

[ptolemy]

Magnacut isn't rust proof. It's very stainless but you can still get stains of course...I have stains that look similar on my s90v. That being said magnacut is still quite a bit more stainless than s90v though. My magnacut in the kitchen has no stains at all through.

What was the longest you let it sit before cleaning?

no more than 1 minute or likely less. I always cut food, then rinse it right after, Maybe i let knife sit while I put food in the pan, but no for more than 1-3 minutes max

 

[ptolemy]

the maker did tests on other magnacut billets he has and different acids + onions and no issues, so we gotta figure out wtf did I do!!!!

i only cut onions, potatoes and carrots.....

 

[DHunter86]

the maker did tests on other magnacut billets he has and different acids + onions and no issues, so we gotta figure out *** did I do!!!!

i only cut onions, potatoes and carrots.....

Could it be stains from carrots? Try a little cooking oil with a kitchen towel to see if it comes off. Carrot stains are notoriouslu hard to clean.

 

[Justinv]

I don’t think its worth worrying about. You can probably fix it in seconds with some flitz. Or rub it on a loaded strop.

 

[ptolemy]

I don’t think its worth worrying about. You can probably fix it in seconds with some flitz. Or rub it on a loaded strop.

ya, not worrying, just wondering, since it's SS and my prev one was very resistant.. i figured someone may have some more insight or experienced same

 

[chiffonodd]

ya, not worrying, just wondering, since it's SS and my prev one was very resistant.. i figured someone may have some more insight or experienced same

i've gotten some weird cloudy water/acid staining on SS cladding before. this looks kinda like that, just .... bigger?

 

[MSicardCutlery]

I might have some insight on this.

Someone who purchased one of my knives had this happen so time ago. I didn't know how to account for it, but according to the internet it is not an isolated phenomenon. My best guess at the time after doing some reading was that there was steel residue left over from the 52100 I had previously used the same finishing belt on, and that, that was what caused it.

Another thing to note, corrosion resistance has two measures. Straight rust resistance, and pit resistance. Those aren't the same. Steels can be higher in one or the other and that will on paper, give that steel a higher overall mark in terms of corrosion resistance. The darkest I have ever been able to etch MC with FeCl, is a very light grey, but it did etch a little. It did start to pit too though. Though the overall corrosion resistance is much higher for MagnaCut, when immersed in FeCl, AEB-L does not appear to etch anywhere near as fast as MagnaCut and does not seem to pit.

 

[TeaThyme]

I had something similar happen to me just today. I was cutting citrus for marmalade and got called urgently. The knife sat there uncleaned for 30-40 minutes. After finishing everything I cleaned the knife and noticed a weird layer. It looked like the polish had changed and but no red rust colour. The surface was coarse if I ran my nail over it. Unfortunately I already scrubbed it away.

Is your patina also coarse?

Has anyone experienced anything like this? Looks like cloudy patina, not your typical one that you get on carbon steel knives. Any insight to what could have caused it? My thinking it's the onions... but why? magnacut is pretty rust resistant

Any insight would be appriciated!

 

[ptolemy]

I might have some insight on this.

Someone who purchased one of my knives had this happen so time ago. I didn't know how to account for it, but according to the internet it is not an isolated phenomenon. My best guess at the time after doing some reading was that there was steel residue left over from the 52100 I had previously used the same finishing belt on, and that, that was what caused it.

Another thing to note, corrosion resistance has two measures. Straight rust resistance, and pit resistance. Those aren't the same. Steels can be higher in one or the other and that will on paper, give that steel a higher overall mark in terms of corrosion resistance. The darkest I have ever been able to etch MC with FeCl, is a very light grey, but it did etch a little. It did start to pit too though. Though the overall corrosion resistance is much higher for MagnaCut, when immersed in FeCl, AEB-L does not appear to etch anywhere near as fast as MagnaCut and does not seem to pit.

ty for the residue, kinda interesting idea. this did have a perfect satin finish, which I imagine meant that it went through other types of buffing after which should have removed the residue, but I will check

as to other question, no this residue is completely smooth, nail doesnt touch it or rubber eraser, only scotch brite and only after very deliberate buffing

 

[MSicardCutlery]

ty for the residue, kinda interesting idea. this did have a perfect satin finish, which I imagine meant that it went through other types of buffing after which should have removed the residue, but I will check

as to other question, no this residue is completely smooth, nail doesnt touch it or rubber eraser, only scotch brite and only after very deliberate buffing

If it's a residue I imagine that something like BKF would strip it.

A perfect satin finish is usually achieved with a surface conditioning belt such as scotchbrite. They often last for a few blades, unlike grinding belts, of which a few get used making just one knife.

 

[Andrei]

Hi all!
This knife was made by me, I am also at a loss as to what it could be.
I would like to immediately exclude a number of questions.
1. I know about abrasive hygiene and the pre-finish and finishing tapes are different for rusting and stainless steel.
2. There is no varnish or anything like that on the blade, it is finished with Р-320 tape.
3. There is absolutely no doubt that this is a genuine MagnaCut.
In my practice, I encountered something similar on the M390, but these stains were less noticeable, and I did not identify any kind of system. After regrinding the blade, this stain no longer appeared on one knife, but on the second it appeared within the same boundaries and of the same shape.
I decided to do a primitive test of this MagnaCut.
I have this steel in two thicknesses, so I decided to test both strips.
The following aggressive media were involved (from left to right): citric acid solution, salt solution, onion, ferric chloride, phosphoric acid and hydrochloric acid.
I diluted solutions of citric acid and soda until the crystals stopped dissolving, squeezed out the juice from the onion and put a few pieces on top.

Also, the first knife I made from MagnaCut, as an edge retention test, spent about a month in a professional kitchen, and there were no marks left on it, the steel was from the same batch.

Three and a half hours passed and what I saw was that citric acid, salt, onion, orthophosphoric acid did not leave any traces, although I was sure that the brine solution was supposed to harm the steel. The darkest stains were left by ferric chloride, but I must say I applied two drops of ferric chloride to each area, concentrated and a regular etching solution, the stain remained only from the concentrate.
Although hydrochloric acid did not leave such a dark stain as ferric chloride, it caused the deepest damage.
This test did not shed any light on the cause of the stains and leaves open the question of what causes this “patina.”
I'm sure Ptolemy nothing to do with the appearance of this patina, because it is stainless steel. He also has a second small knife and both knives are made from the same strip of steel, which has not tarnished.

 

[Andrei]

One more question needs to be clarified, the “decarbonized layer.” This steel underwent heat treatment in stainless foil bags, I removed 0.5-0.7 mm from the surface of the steel. I think this is enough to remove the decarbonized layer in this situation.

 

[jedy617]

Could it have something to do with the heat treatment? I know that can effect corrosion resistance....that being said this doesn't look like "corrosion" per say and it seems like it's quite stainless still

 

[Andrei]

I think not, but I'm not sure about it.
It seems to me that the only logical explanation is the reaction of something on the surface of the blade with onion juice.

 

[MSicardCutlery]

I considered the possibility of decarb too, but it's pretty easy to see visually. Whatever causes it, it's certainly anomalous and infrequent.

 

[ptolemy]

I got some pro scotch brite (320 800 1200) and spent about an hour on it... First of all, i suck and never done this before and my technique kinda sucks... It's also quite slow process and I have almost no power tools and wouldn't trust it even if I had any.

Seems it made steel more brushed finish and removes some staining but the main park sorta because different (see pic) and this made me wonder if the cloudy stuff I saw (as it looks very similar to what seems to be CLEAN now) somehow changed to there being more staining on other parts... sorta bizzarre. My guess i'd have to go back to 60, and spend a lot of time on that and then progress but that's a 6hr+ process and ill likely screw it up. Other parts would be get motorized polisher or grinder and use a cotton polishing pad with a paste but then it'll sorta kill the nice finish.

I will leave it as in and will lileky update this thread if something changes, but going to use this as a baseline

 

[Keithpaints]

Been using Bradford Magnacut for a while we both use it since it's stainless.
Cut fruits, citris, tomatoes all the time with it. No staining at all. I figured since it was monosteel instead of clad it would stay stainless throughout the blades long life. I wash & dry as a habit using carbon knives so many years. She leaves it around it is low mantainence blade.

 

[Redwax]

I have a knife in LC200N that has similar patches on the face of the primary grind. LC200N has better corrosion resistance to Magnacut. I have used the knife heavily around salt water and cutting lemons and limes and there has never been any sign of any corrosion over years of use. The discolored patches remain on it to this day though.

I always put it down to maybe some contamination during grinding or something but that's a complete guess. It hasn't bothered me that much to look into it further.