Marks on Worktops

[garash]

Hi, I think I need a Scientist for this; twice after leaving a tin can on top of my (oiled) Worktops I have been left with a ring mark which I cannot get off. The tins were both clean and dry. What is causing a reaction to the metal to make it do this?

 

[RandomGrinch]

Possibly?

https://www.finewoodworking.com/2018/10/10/remove-iron-stains-wood

...and some confirmation for oxalic acid:

https://diy.stackexchange.com/quest...ngs-on-a-wood-kitchen-top-formed-by-a-tin-can

 

[foxhole]

Tannic acid in oak corrodes some metals.