Three weeks after Easter in 1961, at Glasgow’s red-brick, resplendent, rococo Kelvingrove Art Gallery and Museum, a 22-year-old man took a rock to Salvador Dalí’s enigmatic 1951 painting “Christ of Saint John of the Cross.” At a red museum in a green corner of a gray city, out of a surfeit of zealous religious conviction, a vandal had torn an eight-foot gash in the body of Christ. It would not be the only act of vandalism perpetrated against the Dalí painting, for a little less than two decades later, another aspiring iconoclast took an air rifle to the canvas, though this time curators had seen fit to seal it behind a thick layer of clear acrylic in preparation for precisely this possibility.…