What material is used for Picasso's sculpture in Chicago that creates a rust-like protective layer?

The material used for Picasso's sculpture in Chicago that develops a rust-like protective layer is Cor-Ten steel. This unique alloy is designed to form a stabilized surface layer of rust when exposed to the elements, which acts as a protective barrier and prevents further corrosion. Cor-Ten steel is often favored in outdoor sculptures and structural applications because it combines durability with an attractive patina that evolves over time.

Unlike stainless steel, which is engineered to resist corrosion without experiencing rust, Cor-Ten steel embraces the corrosion process to enhance its aesthetic and protective qualities. Additionally, aluminum and bamboo do not exhibit similar properties regarding rust-like layers; aluminum is lightweight and resistant to rust but does not change color in the same way, while bamboo is organic and unsuitable for large-scale sculptures in harsh climates. Thus, Cor-Ten steel’s distinctive ability to form a protective layer while contributing to the sculpture's visual character is what makes it the ideal choice for Picasso's work.