WHEN the Metropolitan Museum of Art makes a big curatorial decision, it tends to do so with the kind of grave deliberation that goes into a papal bull. Gut feeling is not a prized consideration. But in the spring of 2009, in a dust-covered basement workshop in Fez, Morocco, a young curator in the museum’s Islamic department sat among a group of artisans — workers in traditional North African tile, plaster and wood ornament whose roots stretched back seven generations in the trade — and asked the company’s chief executive yet again why the museum should enlist them for an unusual mission.