Various people, including Shearer, have tried to follow Duchamp's protocol, but they have consistently failed to duplicate his results, even roughly. "Something was very wrong," Shearer insists. Moreover, threads of comparable diameter and elasticity laid down on top of Duchamp's mounted threads wouldn't hold those shapes.

When Shearer and her colleagues examined the artwork itself, now at the Museum of Modern Art in new York, they were shocked. Visible through the glass base were the ends of the threads, poking through from the side normally open to view, and they were glued to the back.

In effect, each thread forms a stitch. Ironically, the French word stoppage also refers to invisible mending or sewing.

No one before seems to have noticed or paid attention to this detail, Gould says.

Rather than simply recording chance events, Duchamp apparently manipulated his materials to create a convincing illusion of chance. Yet by putting the canvasses on glass bases, he didn't hide that manipulation. The clues were there for anyone who looked closely.

Indeed, Herbert Molderings of the University of the Ruhr in Bochum, Germany, argues that Duchamp's artwork is not the result of a physical experiment. "It does not propose any new standards for observing and measuring the material world but establishes the standards of a certain intellectual attitude," he says.