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Several years ago, the National Building Museum in Washington D.C. decided to put on a show to explore both traditional and modern building materials in innovative ways. Stanley Tigerman was curator of the exhibit, and he picked Jeanne Gang to be one of the four participants. “She's good,” he says in explaining the choice. “It's that simple. She's talented, she's very intelligent and she's real Chicago, which means it's about structure and construction. It's not about just the arbitrariness of design.”

The materials in the 2004 exhibition, Masonry Variations, were stone, brick, terrazzo, and AAC, a form of concrete made lighter by being injected with air. Each material was assigned a team composed of an architect and a craftsmen who would have in depth of traditional materials that most modern architects lack. In Gang's case, she was paired with Matthew Stokes Redabaugh, a master stonemason with the International Masonry Institute.

“When Stanley Tigerman told me our material was going to be stone, I was really disappointed. I really wanted that high-tech AAC material.” Tigerman, however, was unrelenting, and Gang was soon confronted with the limitations of the National Building Museum itself, originally Montgomery C. Meigs' 1887 Pension Building. “When we toured the gallery,” she recalls, “we found the floor loads could only take 60 pounds per square foot, equivalent to the visitors who are coming in to the gallery. It was immediately apparent that there was not going to be this heavy stone thing sitting on the floor.”

“I looked up, and there's a vault. That's going to be strong. The building had amazing brick vaults in it. If we could hang it from the ceiling somehow, that could take almost all the load off the floor. So the whole project became about how to hang this stone -to get it off the floor”

Stone works best in compression, big blocks of it piled up one atop another. Hanging stone puts it in tension, the forces pulling at it laterally. This is just not done. When you see a building faced in stone, it's not just hanging there - each individual piece is supported by its own brackets.

“Luckily we had the access to the IITMaterials lab,” says Gang. “They have all of these books about stone, that have big beautiful color photographs, with all kinds of figures on the back,” all kinds of specs describing a particular stone's properties, but strength in tension was not even measured.

“You guys are nuts,” Gang recalls lab professsor Sheldon Mostovoy telling them at the beginning, but that didn't stop Gang's from devising an intricate testing process to arrive at the right stone.

Master mason Redabaugh help guide them to the right choice. “Masons know how stone is going to perform by thumping the stone,” says Gang. If you thump a piece of granite, it will emit a dull, dead sound. "It has little crystals in it,” explains Gang, “Granite is not homogenous so it has a lot of possibilities to fracture. Marble is more fluid - it sounds more like a bell." And so marble it was. But in tension, how much weight could even marble carry?

Professor Mostovoy's lab had a testing device that was like a medieval rack for stone . He originally thought that a piece of stone would be unlikely to bear more than 250 pounds before breaking. “I think the first one broke at about 750 pounds,” recalls Gang, “ and that was good news, because the whole piece was very thin and lightweight, so we knew that if we could hold that much,” they'd be home free. By the end of the tests, they came up with stone pieces that held up to 1,750 pounds before fracturing.

To keep the curtain light, Gang's team turned to state-of-the-art waterjets. “You can't believe how thin, how close you can cut with these things,” says Gang. The individual stone pieces were cut to a mere 3/8 inch in thickness.

The next question would be what shape the individual pieces making up the curtain would take. “How are you going to hold it up?,” Gang recalls asking. “ How does one stone hang from another? You could do a dovetail, I guess, but that would have sharp corners, so we thought of this soft, puzzle-like, interlocking thing.”

Then there was the issue of safety. If one of the 619 interlocking pieces got smashed, how do you keep the rest of the curtain from crumbling like fractured safety glass? “We knew we wanted this redundancy” recalls Gang, “ and we were very interested in the properties of glue. Usually architects are really embarrassed about using glue. They try to deny it, but it's actually one of those materials that's doing a lot of work and never gets any credit, so I like it.” Eventually a fiberglass resin was used, and squeezable bearing pads placed between the stones to avoid direct stone-to-stone connections.

Assisted by modeling studies by the engineering firm of Thorton-Tomasetti, the Gang team arrived at the curtain's final form. A temporary tower of wooden formwork went up to support assembly, beginning with the aluminum anchors that hung the curtain from the vault's ceiling. For Redabaugh, it was all a little different. “How many masons do you know,” asks Gang, “that start from the top going down?”

“Spectacular,” is how Tigerman describes the final result - a stunning hanging curtain made of super thin translucent marble, tapering out like the foot of a snail as it made its way to the floor. The entire structured weighed only 1,500 pounds. “The material that was the strongest“ concludes Gang, “ was incrtedibly beautiful and had a lot of variety to it. We lit it from behind. Mark [Schendel] picked out the lighting that would bring out the most color, difference in color - incredible differences all out of the same stone.” In the nearly seven months that the piece was on the display, the only mishap was a single hairline fracture on a single piece along the bottom. Gang's installation won the $10,000 Grand Prize in the 2004 PRISM Stone in Architecture Awards.

Architect Louis Kahn used to famously posed the question of, “What does a brick really want to become?” “I want an arch,” was the somewhat anti-climatic answer Kahn heard. Gang's marble curtain suggests that, when talking to materials, we may want to listen a little harder.

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© Copyright 2006 Lynn Becker All rights reserved.