Zinc discoloration

[Abyone]

This relates to a discoloration of zinc although not part of a roof but as it's the same material as the zinc on roofs I reckon this is the place for my query.

I have zinc cladding on my windowsills but two of them have discoloured badly. There are pinkish lines and an overall variable tone to the zinc unlike my other windows.

I have tried cleaning but no effect
The only unique thing about the two discoloured windowsills is that one is in a brick wall and the other in a stained cedar clad wall, all my other windows are in a rendered wall and should no signs of discoloration.

Not sure if the lines are brush marks and someone may have wiped a brush on the sill in the last and some chemical reaction happened with what was on the brush. It's only a guess but only thing I can think of.

Would sanding be an option ?

 

[Wayners]

I had to look this up to fact check myself and I would advise phoning the technical helpline for further advice but, you can use patination oil

 

[Abyone]

Do you think I could sand or polish it away - it seems to be the surface of the zinc that is effected not a deposit sitting on top of it.

 

[Wayners]

Try cleaning vinegar maybe.