The series of alloys made use of is magnificent: weathering steel for aging, marine-grade aluminum for weight savings

https://www.scribd.com/document/1039869947/Salvo-Metal-Works-and-the-Truth-of-Copper-Personalized-Chimney-Shrouds-that-Endure-183965

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