The series of alloys utilized is magnificent: weathering steel for patina, marine-grade light weight aluminum for weight cost savings

https://www.scribd.com/document/1040872073/Finials-That-Finish-Well-100-Years-of-Copper-Integrity-143726

The range of alloys used is spectacular: weathering steel for aging, marine-grade aluminum for weight savings, and duplex stainless for rust resistance in extreme environments.