Which material became so synonymous with architect Frank Gehry's brand identity that he later designed a collection of jewelry using it?

In architecture, certain materials have become synonymous with specific architects' brand identities, creating instant recognition of their work. These signature materials often define an architect's aesthetic philosophy and approach to design. This trivia tests your knowledge of the relationship between famous architects and the materials that have become central to their brand identity and recognition in the architectural world.

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Titanium
Corrugated cardboard
Brushed aluminum
Twisted stainless steel