A Sudden Glimpse to Deeper Things: Mark Cousins’s astonishing portrait of Scottish abstractionist Wilhelmina Barns-Graham

Though she was bad at navigating the art world, the painter Wilhelmina Barns-Graham was remarkable at the art. The 20th-century abstractionist, who worked alongside Barbara Hepworth and Ben Nicholson in post-war St Ives, used to paint tussling rows of identical squares and emphatic black lines that bisected at peculiar and erratic angles. Unravelling – or at least understanding – these mysterious formal arrangements is central to Mark Cousins’s humane portrait of the artist, which also works in part as a petition for a more public legacy for Barns-Graham. But this impressive documentary, guided by Cousins’s rhythmic narration and Tilda Swinton voicing Barns-Graham’s journals, is surprisingly light-touch on biography: Cousins seems less interested in historicising the artist within the canon than in accessing her specific, coded point of view.

The approach works astonishingly well, because the haphazard geometries of Barns-Graham’s work are still so unresolved. From childhood, she seems to have been formidably attuned to forms; she had synaesthesia, associating different colours with letters of the alphabet, as well as a strong mathematical sensibility. Together, these elements allowed her to begin creating her hieroglyphics of emotion. For Cousins, the materiality of brush on canvas is secondary to what he calls Barns-Graham’s “brain-machine” – her alchemical mind, which had a hypersensitivity towards nature that seemed to overwhelm as much as it inspired. With this overarching sense of Barns-Graham’s artistic personality, Cousins avoids the teleology of some films about painters, which obsess over the development of work from juvenilia to masterpiece: the film’s generosity of perspective makes it all seem so rich, so worthwhile.

Throughout, Cousins speculates on the limits of documentary, its inability to offer the proximity to a subject that a filmmaker implicitly craves. The techniques he uses to try to enter Barns-Graham’s experience – slide-shows of archive material, animations of her colliding painted blocks, reconstructions of events – turn elegiac: they are symptomatic of a documentary-maker who can invent modes of access, but never reach the real thing. Cousins may have elaborated too much towards the end of the film, however, which includes a video work imagining a conversation between Barns-Graham’s younger and older selves. It’s a rare moment when the film seems to intervene too heavily. The most sublime sequence has a group of Barns-Graham’s pictures appearing on screen, one after the other, beneath the sound of strings. When Cousins curates lightly enough, the work can speak for itself.

► A Sudden Glimpse to Deeper Things arrives in UK cinemas 18 October.