Surely only a double-act of the stature of Philippe de Montebello, the director of the Metropolitan Museum of Art from 1977 to 2008 but also a colossus of the art world more generally, and Martin Gayford, the eminent critic who has doubled as the recording angel of the pensées of Lucian Freud and David Hockney, could have sold the idea of producing a record of conversations about looking at works of art to a publisher.