That's obviously what I suspected - as I wrote:On copper, nah! I can take you to locations where there are miles of pre WW2 copper conductors in the air in ex-industrial areas that was subject to all manner of pollution, that apart from some oxidation on the outside is as good as the day it was put up.
I suppose it must, to some extent, but copper pipes buried in plaster don't usually seem to suffer from more than pretty minor surface corrosion.
Kind Regards, John