What were the circumstances under which the museum acquired the Louis Sullivan metalwork?
The pair of balusters on view on the 4th floor were gifted to the museum by Carson, Pirie and Scott Co. in 1971.
I'm not certain why pieces of the architecture were removed from their flagship store in 1971. Perhaps they were just remodeling. I do know that in the 1960s and 70s many historic buildings were being demolished and or significantly renovated. These losses to architectural history led to the creation of "landmark status" and other preservation measures.
I did happen to find a slideshow published by the Chicago Tribune that includes an image of these balusters on a staircase!
Thanks for looking!