‘Sky Ladder: The Art of Cai Guo-Qiang’ is an Endearing Portrait of an Explosive Artist

Any documentary about an artist needs to show you his or her work and make you appreciate their craft, even if you don’t have a taste for what they do. That’s the minimum of expectation for a film like Sky Ladder: The Art of Cai Guo-Qiang, which focuses attention on the Chinese visionary of the title. Directed by Kevin Macdonald (One Day in September), …