The work of William "Bill" Turnbull is not easy to get along with. It challenges, not becuase it shocks and awes, but for the opposite reason: becuase it is wieghty, quiet, and constant. Yet, as an insightful new documentary reveals, Turnbull's reputation and influence in the art world and among the few who have taken time to get to know his body of work, is profound. Now approaching 90, the modernist sculptor is a relic from an era when art was considered a noble enterprise. In the 1940s the Dundee-born artist assumed the pose of humble, hard-working artisan and - in spite of the acclaim that followed - has remained unchanged ever since. It’s thanks to the dogged persistence of this film’s director, Turnbull’s son Alex, that this documentary can unearth the curiously individual story of such a secretive artist. Perversely, given Turnbull's reluctant celebrity, the film is narrated by Jude Law and received a glamorous reception in Los Angeles earlier this year. 'Beyond Time' presents Turnbull as an artist’s artist. Among familiar interviewees are Peter Blake and Antony Gormley (Turbull “unhitches the relationship between scale and size… makes a very small thing [inspire you to] think of something enormous”). There’s also a poignant interview with his late great friend and close collaborator, the pop artist Richard Hamilton with whom he set up The Independent Group in the 1950s, along with the sculptor Eduardo Paolozzi. Nicholas Serota, the director of the Tate galleries, also a friend of the artist, features heavily. “People are always suspicious of polymaths,” he says, explaining why Turnbull's body of work which varied from figurative sculpture to Anthony Caro-esque steel-based minimalism and abstract painting, is less easily recognisable than, say, a Henry Moore. Turnbull has lived and worked through the art world’s multiple 20th-century reinventions, sometimes at the very forefront of change. He was among a small group of sculptors who represented Britain at the Venice Biennale in 1952, in a groundbreaking show which introduced the world to Brtiain's post-war "geometry of angst", as the critic Herbert Reed described it. Despite a major Tate retrospective of his work in 1973, Turnbull never became a household name like contemporaries such as Barabara Hepworth. Moving in the right bohemian circles in London and Paris Trnbull developed good friendships with colossal figures including Giacometti and Rothko, but never courted the establishment. Far from it. He comes accross in this film as a badger-like presence in the 20th century’s art history, stubbornly immune to limelight or trends. He emerges quietly from his burrow at well-timed intervals, producing still, statuesque monuments that seem to have come from somewhere earthy and timeless, serving to remind us of art’s very origins. That the documentary was made by Turnbull’s son, the DJ Alex Turnbull, is its unexpected strength. There are some wonderful personal insights: his overriding memory of his time as an RAF pilot during the war is that being alone in the clouds was “absolutely beautiful”, for example. Another highlight is the whole chapter on Bill’s second wife, the beautiful Singapori artist Kim Lim, who died of cancer aged 59, in 1997, but seems to have had a profound influence on Turnbull at a crucial stage in his career. “Bill was the man who stuck to his guns,” the director told his audience at a London screening. For all its irreverence, there's a palpable sense of purpose which makes this film feel somehow timely, larger than its own story.