A good article about an underused resource at the US National Archives:
http://www.archives.gov/publications/prologue/2014/winter/ford.pdf
Coming from the National Archives' "Prologue" magazine, the piece documents the Ford Motor Company's Motion Picture Laboratories. In the thirties, FMC was one of the largest movie production and distribution operations, producing thousands of reels of "Americana in Motion" that covered the early 20th Century. They are now held in the film vault of the US National Archives. Over 95% of the collection is in the public domain and available to view and copy.
