This was something I discovered accidentally … once the copper has
been buffed shiny …mix a very weak solution of any liquid dip
silver cleaner and water …paint on watch it over a matter of
minutes to an hour … first it will turn “brighter” , then if the
solution is not removed , it will start to oxidize to varying shades
of red. The trick is to seal it at the proper degree of coloration ,
as it will continue to darken into brown then black if the air is
allowed to continue to oxidize it.