The problem with making a film about the making of art—be it a painting, an album, or in this case, a dance work—is that knowing how a piece was constructed often depreciates the work itself, demystifying its core and flattening a more personal meaning the viewer may have otherwise attached to it. Still, this documentary from journalist-turned-filmmaker Maia Wechsler is a gorgeous dissection of RainForest, a 1968 modern dance masterpiece from choreographer Merce Cunningham, and the process of its contemporary restaging. Stephen Petronio and dancers from his eponymous New York-based company toil under the sharp eyes of three dancers from the original ensemble to perfect every move. The final performance ties into a centennial celebration of Cunningham, who died at age 90 in 2009. His presence is spine-tingling throughout, whether in the wild, thrilling contortions of the current dancers; the original performers, luminous against an abstract set designed by Andy Warhol; or Cunningham himself, seen in piquant archival footage. The film may not compare to seeing RainForest in its purest form, live and sans context, but no matter: dance nerds and visual art obsessives will find much to appreciate.