The last quarter century has been an extraordinary and turbulent period in the art world. It was a time of creative intensity during which a handful of artists, like Julian Schnabel, Jeff Koons, Keith Haring, and Jean-Michel Basquiat, managed, in their different ways, to cross over from the rarefied world of high art into popular culture. It was also a time when other promising careers and even whole movements, like Graffiti, spurted to life and...