Regina Construction III

[Treesplease]

[QUOTE=Stormer;6750264]Sorry to beat this to death but it seems that in environments with low humidity and low air pollution, the green patina will never form and the roof will stay black:

haha - I also nerded out earlier and read the architectural copper page on wikipeida and was going to post it. It is one of those issues that just leads to more questions the more you look into it.

I also read on some installer forums that there may be galvanic properties at play - if the copper on the roof is in direct contact with any other metals of a lower galvanic number (zinc, aluminum, iron etc) the other metal will corrode first and the copper will stay black. One installer said even something as small as a galvanized (zinc) nail would do it. There are also variants in material other than 99.9% copper. Some copper is actually copper alloy with zinc and lead in small amounts and if so they will corrode to dark brown and not turn black. Most sources said the black to green transition takes many years, 10 to 30 yrs and if we are a low pollutant area and relatively lower humidity we are likely on the long end of that scale.
But you can see the roof starting to turn green on the horizontal parts in the pic you posted earlier. And I talked to others that also vaguely remember that the roof used to be green years ago.