Sondheim has Seurat sing, or rather woof, a little duet between two dogs meeting on the island of La Grande Jatte; later, Sondheim gives Seurat a pointillist melody as he works, crotchet-dabs of blue, blue, blue, red, red… Seurat’s muse, meanwhile, is called Dot. Seeing the National Gallery’s somewhat overloaded presentation made me long for the light touch of Sondheim. ‘Seurat and the movement’s early adopters such as Paul Signac believed these separate dots of pure colour would fuse in the eye.’ Sounds painful. The masterworks here – by Pissarro, Van Gogh and Seurat – are given context by the lesser paintings, which are interesting, too. I leave thinking of Sondheim, who seems to have noticed so much more about Seurat, and humming under my breath, ‘Art isn’t easy…’