When I visited Phoenix to write about Will Bruder’s Agave Library for our March 2010 issue, I took another look at the architect’s Burton Barr Central Library, his masterwork right downtown. Completed in 1995, the muscular building flexes its architectural biceps—a pair of corrugated-metal-clad wings flanking an inward-curving glass entry. To break down the mass of the grand façade and respond to different functions inside the building, Bruder created vertical bands using two types of corrugated copper: perforated and solid. On its short north and south ends, bravado gives way to sensitivity as the architect and his team used ribbons of sail-like shades and other devices to control daylight into the five-story, 280,000-square-foot structure.

The library was packed with people on the mid-week evening I dropped by and the place still looked great. A lot of modern buildings don’t age well, but this one has the rugged good looks of a Western movie star whose box-office appeal stays strong long into his career. Staring at the great swath of weathered copper facing Central Avenue, I noticed, however, a lot of pigeon poop on the perforated bands but none on the solid ones. In Phoenix, where copper doesn't normally turn green, the bird droppings had achieved what the local air couldn't--a lovely patina that added a chromatic rhythm to the elevation.

The next morning when I met with Bruder to tour the Agave Library in the city’s suburbs, I mentioned the excrement on the Central Library’s main façade. “Yes, isn’t it great!” he exclaimed. “It really helps emphasize the different bands.” Seems as though the pigeons hang out on the perforated bands because they can hold onto the holes with their claws. “I must admit, we hadn’t thought about that, but we like the results,” said the architect.

For the next 10 minutes, he waxed poetic about the history of excrement in architecture, noting the way ancient Romans would bury copper near latrines to add patina to their building materials and Frank Lloyd Wright used horse urine to the same effect. I never learned any of this stuff getting my master’s in architectural history at Columbia, but I’m sure Bruder could give a fantastic, hour-long lecture on the topic.