A client asked me to review his architect's specifications for a major restoration of a late 18th century farmhouse. All involved with the project were completely shocked when I suggested they lose the copper porch roofs, valleys and gutters. I recommended that they instead consider terne for roofing and related accessories.
For those not familiar with the material, terne, or terneplate is sheet iron (now steel) dipped in a lead-tin alloy, first produced in the US around the mid 1820s. It was less expensive to manufacture than its predecessor, tin plated iron (similar properties, just less shiny). By 1900 terneplate replaced tin completely and steel replaced iron as the base sheet.
Copper's characteristic green patina, caused by oxidation, is its protective coating. I'm convinced that it doesn't withstand acidic attacks as well as terne. Atmospheric corrosion, most commonly caused by the burning of sulfur containing fuels is likely the most common cause of copper failure. Tannic acid from red cedar or oak shingles of a wall or dormer, lime from the mortar of a chimney, or even bird droppings can also cause local, concentrated damage. I also find a fair amount of copper roofing products or gutter linings failing from fatigue, due to expansion/contraction, that I just don't see as often with terne.
Now I'm sure to pique those in the business of producing and selling copper. I've read several claims from the copper industry that the oldest copper roof in the US is on Christ Church in Philadelphia, installed in 1742. The problem with that statement is that there's documentation that shows the roof was installed in the 1830s and remained until 1967.
There are terne roofs that are documented to be still in service for over 160 years. I was recently involved with one installed in 1848. It needs maintenance, but still has plenty of life.
I also take issue with installing opulent copper details on 200 year old Quaker farmhouse. It'll be a little like seeing William Penn dressed as Mr. T.