The title of Elvis Mitchell’s tremendous study of black American cinema is taken from Ossie Davis’s 1970 Blaxploitation buddy cop comedy Cotton Comes to Harlem, based on the Chester Himes novel, about a bale of cotton discovered in Harlem, of all the unlikely places: a bale which hides misappropriated cash and is of course a satirical symbol of oppression. Different characters wisecrack: “Is that black enough for you?”, riffing subversively on authenticity in the power struggle.

With a dense and fascinating mass of clips and interviews with figures in the movies such as Whoopi Goldberg, Zendaya, Samuel L Jackson and Laurence Fishburne, Mitchell fights back against cultural erasure and amnesia: there is a rich and vivid history of African American cinema which blossomed in Hollywood’s pioneering golden age, but was siloed in designated “negro” cinemas. (Martin Luther King is shown reminiscing about them.) Mitchell recalls unsung, or insufficiently sung, heroes of black moviemaking such as Oscar Micheaux, the first great African American film-maker who was an independent creative powerhouse from the silent age onwards.

Mitchell makes the interesting point that Blaxploitation was reviving old-fashioned verities of characterisation and storytelling, just as the white New Hollywood was questioning them. Dustin Hoffman, Jack Nicholson, Gene Hackman were playing nervy anti-heroes who didn’t know what to make of the world. But there were also African American stars such as Billy Dee Williams who revelled in their masculinity and old-fashioned handsomeness.

But then Blaxploitation came to an end. Why? Mitchell wonders if the financial calamity of The Wiz, the all-black reimagining of The Wizard of Oz, starring Diana Ross and Michael Jackson, had something to do with it; or whether the problem was the new Reaganite conservatism which also put the brakes on the American New Wave.

Either way, Mitchell leaves us to ponder that as this is where his film ends: he looks ahead to film-makers such as Julie Dash, but his film focuses on the 1970s, without making that the explicit subject of the film. What of the decades to come? Is there a distinctively black culture there to be rediscovered or reclaimed or reinvented? Mitchell makes that question the point of entry for everyone considering this. An absorbing and nourishing documentary.