The exterior facade of the Empire State Building was made of a limestone [G 04 / curtain wall], blonde in tone, pierced by [L3 302 / windows] - which can be opened - set flush and trimmed with vertical strips of [L3 203 / stainless steel] running the height of the building. These strips, called [G 10 / mullions], draw the eye upward and make the building seem even [V 005 / taller]. In all, about 10,000 sheets of stainless steel were used. To insure that the metal was rust-resistant, a test strip was cut from each sheet and subject to a salt-water spray for 100 hours. If the slightest bit of rust appeared, the entire sheet had to be rejected.
The interior arches supporting the floors required 62,000 cubic yards of reinforced anthracite cinder concrete. The stone setting and outside wall construction progressed at the rate of nearly a story a day. All of the stonework, except a few ornamental features around the lower floors, was complete in 113 days.
