Home movie footage donated by metro Detroiters provides the spine of “12th and Clairmount,” which looks back at the Detroit riot of 1967 — and its causes and aftermath.  Those five days in July were among the most pivotal — and divisive — in the city’s history, with the turmoil leaving 43 dead. While the impending 50th anniversary of the summer of ’67 was the impetus for the film, the home movie footage in “12th and Clairmount” captures a wide spectrum of Detroit life, from proud streetscapes to dance parties to neighborhood sporting events.  Drawing from more than 400 reels of donated home movies from the era, other unearthed footage and newly recorded oral histories, the documentary is being produced by the Free Press in collaboration with Bridge Magazine and WXYZ-TV (Channel 7) and a group of metro Detroit cultural institutions, led by the Detroit Institute of Arts.