After $10 Million, Effort to Coat Base of Trade Center in Glass Is Halted

The plan was to drape the base with 2,000 clear prismatic glass panels and welded aluminum screens to create, in the words of the architect, “a dynamic, shimmering glass surface.”

But the glass has proved difficult to manufacture at that scale. In trials, the refinishing required for the prismatic effect has left the glass brittle and prone to shatter. With the steel frame of the building now rising to the 65th floor, the Port Authority of New York and New Jersey has scrapped the idea and sent the architects back for yet another do-over.

“As design moved to the testing phase, it became clear that the prismatic glass simply had too many technical problems to overcome and at a budget that was not cost effective,” said John Kelly, a spokesman for the Port Authority. “We have been finalizing a design that will be far more practical while being both distinctive and magnificent.”

About $10 million had already been spent on the glass. David M. Childs of Skidmore, Owings & Merrill, who designed the tower and the prismatic glass covering, did not respond to phone calls seeking comment.

Douglas Durst of the Durst Organization, which owns a 10 percent stake in the building and is in charge of leasing it, said the switch in plans should have no effect on the timetable for the building, scheduled to open in January 2014. The new facade is likely to be made of more traditional clear glass panels, possibly with granite elements to tie it into the surrounding plazas.

The problem with the glass illustrates the tension inherent in the entire $3.2 billion project: how to create a skyscraper that is at once iconic and defended against terrorism, while also containing costs.

In 2003, Daniel Libeskind, the master planner for the trade center site, designated the northwest corner of the 16-acre property for a 1,776-foot tower, which was named the Freedom Tower by Gov. George E. Pataki and later renamed 1 World Trade Center.

Larry A. Silverstein, who was the building’s developer at the time but later relinquished control to the Port Authority, brought in Mr. Childs, a renowned architect who designed the Time Warner Center, among other notable buildings. But Mr. Childs’s design went back to the drawing board in 2005, after the New York Police Department warned of the dangers posed by a vehicular bomb. Mr. Childs, who friends say sees the tower as a legacy project, redesigned the building, shifting the base away from West Street and inserting a thick concrete podium designed to lift the tower out of the path of a blast.

The plan allowed for a lobby with 50-foot ceilings, but no office space until what is essentially the 20th floor.

But Mr. Childs’s plan for a windowless metal facade for the podium prompted some critics to describe it as a “concrete bunker,” which alarmed Mr. Pataki, who was sensitive to the skyscraper’s image. In June 2006, Mr. Childs unveiled a revised design with the concrete base now clad in prismatic glass welded to aluminum screens, to give the base a feeling of transparency. In the event of a bomb blast, the inch-thick glass panels, each one 13 feet 4 inches by 4 feet, were designed to crumble into small fragments the way automobile windshields do.

To make prismatic glass, wedges are cut into the surface to create a prismlike effect, so that the glass will “reflect, refract and transmit light in various spectrums,” according to the architect, without blinding passers-by or drivers. Prismatic glass has been used as a decorative feature for more than a century in lamps and storefronts.

But the World Trade Center plan was unprecedented, at least in the United States, said William M. Yanek, executive vice president of the Glass Association of North America in Topeka, Kan. “To our knowledge prismatic glass has never been used on a building of this magnitude,” he said. Above the base, workers are installing more than 12,000 more traditional, ultraclear glass panels to the building’s steel frame.

Three companies competed for the $82 million contract to manufacture and install the base facade, and in August 2008 the Port Authority selected a joint venture of DCM Erectors and Solera Construction. In an effort to cut costs,

“I’m not sure a more important symbol of our nation than the Freedom Tower will be seen in my career,” Gary R. Danowski, vice president of PPG Performance Glazings, a Pennsylvania glass manufacturer, told an industry publication in 2009. “The thought that the protective skin of this icon of America will be made from glass sourced on the other side of the planet and not local material is quite a blow.”

But with the Chinese manufacturer unable to produce a glass panel that matched the sample from the architect, DCM-Solera ordered the raw glass last October from PPG’s manufacturing plant outside Carlisle, Pa.

The fabrication was still to be done in China, and some panels were sent there beginning in January. It was a complex undertaking involving cutting, as well as laminating and tempering to create the safety-glass effect. But the glass panels tended to bow after they were cut and tempered, which interfered with the lamination process. The ridges cut into the glass also proved to be too brittle and broke into large pieces, rather than tiny pellets.

It is unclear whether an American factory would have been more successful, but after two years and millions of dollars, the Port Authority decided that further trials would not be prudent, and in March it quietly dropped the idea.