Input (grade 13): The sculpture was made from the same weathering steel (also known as Cor-Ten) as the Angel of the North sculpture, which gradually develops a tightly adhering oxide layer as it is exposed to the elements.
Output (grade 9): The sculpture was made from the same weathering steel (also known as Cor-Ten) as the Angel of the North sculpture. This slowly develops a tightly adhering oxide layer as it is exposed to the elements.