Rhubarb changing patina?

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LewRob80

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Been using this Konosuke Fujiyama blue 1 240 (new finish) for about a year as a daily driver. Patina has been pretty set, but after chopping a lot of rhubarb the patina on the core is very blue, while the cladding is almost shiny again? I know the acid in rhubarb would react, but I wonder why it reacts so differently! I have cut lots of onions, citrus and even pickled items, all of which patina the soft iron with more colour.
Any chemistry nuts that can explain?
 

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I'm curious to see the chemists respond, but I think taking a little nibble of raw rhubarb might help answer your question. It's strong!
 
I can't answer your question but it is interesting how different foods can cause such different patinas. Strawberry's turn stuff black.
 
Interested more in the specific acid and how that would effect patina colouration.

The leaves are high in oxalic acid which makes them inedible. I'd imagine the stalks have a lower concentration, but still enough to alter the patina.

Oxalic acid is an active ingredient in Bar Keepers Friend, which can be used to remove patina.
 
The leaves are high in oxalic acid which makes them inedible. I'd imagine the stalks have a lower concentration, but still enough to alter the patina.

Oxalic acid is an active ingredient in Bar Keepers Friend, which can be used to remove patina.

Thanks! Would make sense! I guess the lower concentration left the core steel less affected?
 
I know oxalic acid stings my hands when squeezing spinach. It's also in baking powder, so this would make sense. 👍👍
 
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