Metal use for spiral staircases
To build a spiral staircase, you must use metal and concrete, glass or stone. A spiral staircase requires both flexibility and strength. Metal is the material used most often as it is tough and allows flexibility.
The only downside metal had was it rusted rapidly. This has changed now because of metal treatments and stainless steel development. Metal can be used by itself or be a great addition to a different material staircase.
The most spectacular staircases are made of a combination of wood and steel or wood concrete and steel. Even so, metal remains the material of choice because it can be bent and twisted in many shapes and still keep all its properties.