iron
A staircase supported by cast, wrought, or other iron members, distinguished from a steel staircase frame.
An iron staircase is a set of steps in a built object whose supporting framework is built of cast, wrought, or other iron distinct from steel. The form and mechanical properties of the iron influence the suitable stairway configuration, and iron is used for freestanding staircases (like many helical stairways for example). It is also useful for staircases that bridge a wide space without supporting columns in the middle.
Iron forms the supporting stair members. Cast and wrought iron are included, although their mechanical properties differ.
A surface coating or floor finish does not determine the frame material. A steel supporting frame belongs to the separate steel staircase definition.
