Thankyou for posting that.colin54 wrote: ↑13 Mar 2022, 10:45am Possibly the colour change happens on black anodised surfaces for various reasons, some possible causes explained here :-
https://www.finishing.com/158/25.shtml# ... %20process.
I've seen it happen many times on black anodised surfaces but never known why. That discussion focusses on sealing, and shows that the effect depends on exposure to light. But why does it looks coppery?
Jonathan