Terra Cotta had the benefit of being a factory produced material. And the Railway Exchange is covered with it. Still there was flexibility for special conditions. Like this one at the mainstair. A border of 26 layers (depending on whose counting) transitioning from arc to angle. DID I SAY TWENTY-SIX LAYERS.....???
I can't help but notice that islamic geometry at the return air grill. I first saw this in John Root's work and the Rookery. But it is pervasive in early Chicago School architecture.
One more story to uncover.