One of the most catastrophic and widely reported curtain wall failures occurred in January, 1973, when, during construction of Boston's John Hancock Building, designed by Henry Cobb of then I.M. Pei & Partners (now Pei Cobb Freed & Partners), 75-mile wind gusts caused more than 65 500-lb glass panels to shatter and fall.

More panels broke and fell in the following months and, ultimately, all 10,344 panels on the sixty-story building were replaced, at a cost of $7 million. In the interim, exterior openings were covered with plywood, leading to the joke in Boston that the Hancock Tower should be renamed the U.S. Plywood Building.

Jokes aside, Nicholas Isyumov, research director for the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario, says engineers learned from the experience that they must pay attention to the effects of wind not only on the structure, but also on the nonstructural cladding, especially when that skin is of aluminum or reflective glass.

Despite the occasional calamity, the idea of an all-glass skin remained perhaps the most persistent curtain wall theme of the 20th century. Starting with small metal window systems containing relatively small glass panes, and moving towards larger glass sizes with smaller mullion profiles, the most technically advanced glass walls of the recent past managed to eliminate mullions entirely by using the glass itself as a structural material, relying on structural sealant joints, or pinning the glass to elegantly-detailed lightweight steel sub-structures.