The Isabella Stewart Gardner Museum, vexed for decades by one of the art world’s most dramatic mysteries, cracked a case of less but still some significance when conservators identified the original fabric for a set of chairs in need of restoration in the museum’s Dutch Room—the site of the greatest art heist of all time. That mystery derives from the still unsolved case of three invaluable paintings—by Vermeer, Rembrandt, and Manet—that were stolen by thieves who broke into the Dutch Room in 1990 and made off with artworks whose whereabouts remain unknown. The newer mystery involves the question of how best to spruce up a set of 17th-century chairs to a period-faithful state as part of a three-year restoration of the Dutch Room. Related Articles As reported by the Boston radio station WBUR, “Much of its restoration has consisted of relatively straightforward tasks, like cleaning the painted Italian ceiling and refinishing the floors. But the set of 14 chairs posed a unique challenge. They had been reupholstered multiple times over the years, and the old …