I don’t recall rust, copper, or terra-cotta as colors for buildings and ornamental pieces when I was growing up. Do you? Somehow, somewhere, it started happening in my part of California in the the 1980s. I think. It’s certainly a major force in building colors today, almost a neutral or default color acceptable to most people and settings.
The rusty steel look may have started when a material called weathering steel or COR-TEN steel was first used in the building trades. Perhaps the early to mid-1960s. Green Future says the first architectural use of corten steel (external link) was for the John Deere headquarters in Moline, Illinois in 1964.
Architizer.com says that corten steel is a specialty product (external link), not just stabilized rusty steel:
“Cor-ten steel resists corrosion by incorporating less reactive metals such as copper and nickel into the steel during its formation. The new alloys in the steel form a connective matrix throughout. This ‘sticks’ the rust formed to the surface, creating a protective barrier similar to skin.”
“The outer layer of rust is stable, and greatly increases the physical integrity of the steel. Unlike typical steel, cor-ten does not need to be painted, reducing initial construction costs. Also, weathering steel is maintenance-free; once the rust barrier is formed it is stable. Paint used as a defensive barrier against the elements needs to be maintained since it is unstable and flakes off.”
Other copper or rusty steel colors may have come into favor after the rusty steel look proved popular. Just speculating.
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