The design of the architectural scrim which surrounds the building was changed in September 2012. The proposed building itself was a box-like structure. The three-part corona of the building's design was created by a structure only minimally attached to the building. The exterior of this structure, whose frames lean outward to create the corona, consisted of a thin screen or "scrim" perforated by geometrical patterns based on historic iron grilles found in African-American communities in Charleston, South Carolina, and New Orleans, Louisiana. The original design proposed that the scrim be made of bronze, which would have made the museum the only one on the National Mall whose exterior was not made of limestone or marble. Cost issues forced the architects to change this to bronze-painted aluminum in September 2012. The change was approved by the Commission of Fine Arts, but the commissioners criticized the change for lacking the warm, reflective qualities of bronze. Noted architect Witold Rybczynski also criticized the change: "The appeal of bronze is its warm golden sheen and the rich patina that it acquires over time, but uniformly painted surfaces lack these attributes, and over time they don't age, they merely flake. ... At the time of this writing, the African American museum risks compromising its original intention. In architecture, beauty sometimes really is only skin-deep."