Our copper guttering arrives glowing with a distincitve warm red tone. Within a couple of years depending on the environment in which it is installed it will have dulled to an earthy tone. After something like 20years it may have reached the equally distinctive Verdigris textured green.
You should not attempt to impede this transformation with abrasive pads or brushes.
The sacrificing of the external molecules to oxidisation creates a hard exterior that protects the core of the metal guttering/downpipe or rainwater system fitting (Stop-end, Gutter Angle, Gutter Union, Downpipe Shoe or Bracket etc).
(9month aged Copper in Cornwall)
Although it is possible to speed up this process by painting with acids – we would not recomend that either.
Just be patient, and enjoy seeing the nature take its course and every age of this stunning metal. It is incredibly resistant to harsh environments and run off from acidic timber cladding.