Last month, at Edinburgh School of Art, I was interested to come across a student who’d chosen Marlowe’s Dr Faustus as her end-of-year degree project. In the wonderful stage costume she’d designed for its central figure were three gloriously embroidered butterflies fluttering around his hat. Bats, yes, moths, maybe, but what exactly was the significance of butterflies to a man bound for subterranean hell? The answer is in Rainbow Dust, Peter Marren’s superbly distilled statement on our national obsession with butterflies.