Could this be rust?

[Thpp9]

Hey everyone,

I polished my knife yesterday and cooked some dinner today. I diced some peppers, cut some onions in half and put my knife down without wiping till I peel the onion skin. I would say I left the knife with onyoh juice for about a minute and when I picked it up I came across this:

At first look it definitely seemed like rust to me. Washed and dried the knife to assess the situation. I ran my finger threw the brown area but it didn't feel like rust. I rubbed some paper towel hard on it and it came out clean. At this point I was convinced it was an extremely ugly patina.

I rubbed some stone powder and it disappeared in seconds, leaving me with this:

Judging from all this, could it be actually be rust or some nasty patina on the freshly polished bevel? I firmly believe that it was patina, but I am curious to hear what it seems like to you.

TIA

 

[Troopah_Knives]

looks like rust to me.

 

[HumbleHomeCook]

It does look like rust.

Is that a Manaka? The kasumi finish on mine was pretty reactive at first.

 

[Thpp9]

It does look like rust.

Is that a Manaka? The kasumi finish on mine was pretty reactive at first.

Yes that a Manaka. Cladding is pretty reactive indeed. Honestly it seems like rust, no doubt about that, but what's makes me sceptical is the fact that it left no residue at all on the paper towel. Each other time I had some issue with rust, paper towel came out slightly brown. Also it felt super smooth to the touch, not flaky or rough at all, but that's probably because I caught it pretty early (relatively speaking at least lol)

 

[HumbleHomeCook]

I noticed that on mine early too. I did some light "polishing" on the kasumi of mine and it's been fine since.

 

[Thpp9]

I noticed that on mine early too. I did some light "polishing" on the kasumi of mine and it's been fine since.

Mine is polished as well. The core isn't really reactive, the cladding is reaching Mazaki levels tho
Tbh, polishing it didn't make a huge difference for me, reactivity wise (definitely improved performance by reducing drag, but that's a totally different topic of discussion). In general, I find my knives pretty reactive after fresh kasumi. It's taking a few onions till they settle down a bit.

 

[bahamaroot]

It's patina, if it was rust it would have came off on the paper towel, period.

 

[miggus]

Hmm... my tip is that it was a super thin layer of rust.


This post might contain more details than you wanted in the first place I mean, the differentiation between two terms is a bit complex from a chemical standpoint as far as I (chemical ignorant person) understand that. The main characteristic is that rust is harmful / destructive, while patina isn't. But they're both oxidations. Rust usually is bright red, which means the reaction is active and will continue with further humidity added. Darker brown or other colors usually mean the reaction is not active and will not continue.

At least this is how I know it from handling tetsubin (cast iron water kettles). These always rust, but what one wants to look out for is bright red spots, these are dangerous. Darker brown is not an issue. Also, it's possible to deactivate the rust with boiling it in strong green tea - it will turn from red to brown then.

What is passivation?​

Passivation, generally associated with stainless steel, is a treatment method to protect the metal from corroding through—making the material “passive” to the surrounding environment. Passivation, perhaps counterintuitively, encourages corrosion to occur on the surface, creating a thin layer of a new, non-reactive chemical. This top layer stays tightly bound to the metal, creating a natural seal that blocks the elements from corroding subsequent layers of the metal. A metal is passivated when every surface is covered with a tightly bound layer of corrosion. This layer may build naturally (passively) over time, but manufacturers can also actively induce it.

https://www.reliance-foundry.com/blog/passivation
Unless I'm mistaken, a patina is basically a passivation.

As I said, I don't understand the precise chemical background. But bright red is very often rust. But if the layer is thin and you clean it off not too late, it shouldn't matter.

 

[Benuser]

It's patina, if it was rust it would have came off on the paper towel, period.

Agree. If it feels rough, it's rust. Rub on it with a thin towel — I like linen. Get it smooth. Rinse with it a lot of hot water. Once it doesn't stain the towel it is for sure a patina.

 

[tim huang]

Hey everyone,

I polished my knife yesterday and cooked some dinner today. I diced some peppers, cut some onions in half and put my knife down without wiping till I peel the onion skin. I would say I left the knife with onyoh juice for about a minute and when I picked it up I came across this:

first look it definitely seemed like rust to me. Washed and dried the knife to assess the situation. I ran my finger threw the brown area but it didn't feel like rust. I rubbed some paper towel hard on it and it came out clean. At this point I was convinced it was an extremely ugly patina.

I rubbed some stone powder and it disappeared in seconds, leaving me with this:



Judging from all this, could it be actually be rust or some nasty patina on the freshly polished bevel? I firmly believe that it was patina, but I am curious to hear what it seems like to you.

TIA

Hey everyone,

I polished my knife yesterday and cooked some dinner today. I diced some peppers, cut some onions in half and put my knife down without wiping till I peel the onion skin. I would say I left the knife with onyoh juice for about a minute and when I picked it up I came across this:

View attachment 201242

At first look it definitely seemed like rust to me. Washed and dried the knife to assess the situation. I ran my finger threw the brown area but it didn't feel like rust. I rubbed some paper towel hard on it and it came out clean. At this point I was convinced it was an extremely ugly patina.

I rubbed some stone powder and it disappeared in seconds, leaving me with this:

View attachment 201253

Judging from all this, could it be actually be rust or some nasty patina on the freshly polished bevel? I firmly believe that it was patina, but I am curious to hear what it seems like to you.

TIA

the blue colour tells me it's more likely a patina rather than rust.