On 29 February 1972 the English artist Keith Vaughan went to see an exhibition of Mark Rothko paintings. Vaughan recorded the occasion in his diary: "To Hayward Gallery in the afternoon to see Rothkos. Feeble stuff. Large décor. Boring to paint and look at. Not surprising he killed himself if that was all there was to do." This is both ironic and shrewd. Ironic in that Vaughan was also to kill himself five years later (though for reasons unconnected with his art) but shrewd in that, even in this throwaway remark, he gets to the crux of our responses to Rothko and his huge, darkly luminous paintings.