They’re not hanging from anything. Courtesy of Suyama Space

Every building you're in makes you do things; architecture stages you. Two 20-by-40-foot stage curtains made of ghostly white plaster are the latest installation at Suyama Space, the art gallery in an architectural firm downtown. They're at either side of the gallery facing each other, fragile towers. Incredibly, the curtains stand on their own, without being hung from anything. It took artist Ian McMahon an entire month to build them, and on opening day, a courier caught the edge of one curtain with his delivery and tore off a segment, which crashed to the floor. That was foreshadowing.

Cascade is the title of the installation. McMahon drove his supplies from upstate New York where he lives: scaffolding, compressor hoses, spray bottles, metal track channels, enormous roofing rubber sheets, a homemade winch system with a bicycle pedal for a crank. The 4,000 pounds of bags of plaster dust met him here. To keep the noise and dust from the architects, he worked nights. The architects came in every morning in greater and greater disbelief. They did not believe the curtains would ever stand alone.

Beth Sellars, the white-haired woman sweeping up after McMahon's nights, is the curator who chooses the artists. She founded Suyama Space 16 years ago, and when she tells me one afternoon after sweeping that Suyama Space can't go on forever, I crumple a little inside. Since the first installation in 1998, featuring Lynne Yamamoto's homage to her grandmother's life as a picture bride and a sugar plantation worker, Suyama Space has given numerous artists—Lead Pencil Studio, Alex Schweder, SuttonBeresCuller, Claudia Fitch, John Grade—rare experience working large, and up against a piece of distinctive architecture. Every artist who creates a piece for Suyama Space has to respond to the soaring room with its old wood beams and light raking in through long rectangular skylights. Many of these installations have been extraordinary. Sellars is extraordinary. Cascade, too.

McMahon made a smaller freestanding plaster curtain once before. But it was solid and stood for only a matter of hours. These gigantic curtains have to survive for three months. They are parted in the center, adding structural precariousness in order to form a functional doorway that welcomes a performer. Entering the building, the first parted entrance is before you, directing you to walk through; when you do, you're in the "onstage" area between the two curtains. Because the curtains are mirror images, you can also walk through the opposite parted entrance to enter the architects' office.

Industry never intended these uses of plaster and rubber. McMahon had to invent the process under restrictions: House rules forbid driving nails into the ceiling beams. McMahon developed an elaborate system from which to suspend metal tracks. He hung the heavy rubber curtains from the tracks. When the folds were arranged just right, he sprayed liquid plaster on one side, starting at the top. He did this for weeks. Layer upon layer. The plaster built up on the enormous vertical surfaces, but also oozed down and formed lava-like pools on the floor.

After McMahon decided the plaster was thick enough, he let it dry, then peeled away the rubber by hand like the peeling skin of a sunburn. Now hanging loose, the rubber curtains were detached from the track and gingerly pulled down, rolled onto the winch drum. That left two huge, entirely freestanding, cascading facades of plaster. Their only footing is the plaster pools on the floor, and their only other attachments are small metal tabs at the top to prevent sway.

One side of each curtain is still craggy and gloppy from the spraying, like the bumpy, crawling wall of a cave. This side faces outward, the roughness indicating that you're in the backstage area. McMahon also left his scaffolding there, his own staging materials. The craggy sides of the curtains are recordings of what happened to get to this point. The other sides of the curtains are stage magic.

Between the tall curtains, it's ceremoniously dark. Up top, backlit by natural light coming through the windows, the curtains' pleats have extra-crisp edges. The edges draw white lines in midair that form abstract shapes and inscriptions. The curtains are creamy and liquid all the way down to where each pleat gathers in a silky bunch at the floor. These smooth, trompe l'oeil faces are strangers to their stormy backs. Gravity seems reversed; the curtains stand rather than hang.

If McMahon gets permission, he will conclude Cascade by swinging a single metal bar at the curtains, and they will vaporize in an instant. Most large-scale works are expensive denials that any crash could be coming. These were built to be destroyed. The atomized fragments will float in place for the tiniest moment before they fall to the floor in a heap. Sellars will sweep them away. recommended