Shiny Layer Between Cladding and Core Steel?

My stainless clad Takeda gyuto has been developing a patina which allowed me to see something odd with the blade construction. Before the patina you couldn't notice much difference between the core steel and the cladding (non KU part). Now it's almost as if there is some core steel which refuses to develop a patina. I thoroughly cleaned the blade so am certain it isn't some sort of lacquer or coating preventing oxidization. It sort of has a distinct appearance from the cladding too so it isn't jigane (it seems to be between the cladding and core steel). It only really seems to be at the heel and at the tip.

Left side at towards the heel:


Left side at towards the tip:


Right side at towards the heel:


Any idea what it is (flux?) and if it may be problematic? I'm looking into a rehandle for this knife and don't want to "invest" in it if there is risk of an issue like de-lamination or something.

Thanks KKF

Non-KU portion of stainless cladding perhaps?

Edit: nm you mean just those spots. No idea

I'm pretty sure it's carbon migration, some of the carbon from the core steel moved into the stainless cladding during forge welding.

It's also possibly a layer of nickel placed between the core and cladding steels. This would be done to prevent the above mentioned carbon migration.

This happens more dramatically on Hiromoto blades. Thinned ones especially.

this happens more on stainless clad carbon blades... i believe it is carbon migration and its effects on polishing, but someone like devin would know better than i do

Thanks for the responses all, it sounds like this isn't the first time someone's seen this. You can almost see a "lamination line" (if you want to call it that) between the shiny layer and stainless cladding which made me think it wasn't the cladding itself, also you can see the core steel right at the edge.

I'm hoping it isn't a blob of something thru the core steel and rather is just a thin layer between the core and cladding. I'll see about taking a few passes on a stone to see if it'll do anything.

I always thought it's a layer of nickel used to bind the stainless clad to the core steel, I'd be more than happy to find the correct answer here.

carbon migration, nothing to worry about

Good to hear it's not a problem. I did a quick pass over a 1k stone as a test and then forced a quick patina and it seems to be gone, you can actually see that the lamination line hasn't really moved at all:


I wonder if this is what's also going on with my 275mm stainless clad white#1 Funayuki; on the left side it's definitely core steel at the tip, and on the other it looks like a semi stainless or something. Doesn't seem to affect performance at all though

sachem allison said:

carbon migration, nothing to worry about

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Yep

ThEoRy said:

This happens more dramatically on Hiromoto blades. Thinned ones especially.

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Any specific reason why the effect is so awesomely, dramatic looking on the Hiromoto blades?

MadDurrr said:

Any specific reason why the effect is so awesomely, dramatic looking on the Hiromoto blades?

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I believe what you see on Hiromoto blades, especially thinned ones is not a carbon migration; it is a awesome contrast between core and laminated steel. Core carbon steel oxidizes (patinas) while the laminated stainless stays pure. And the deep color of patina is probably due to some properties of AS.