This is a fascinating article about the “Mostly Lost Films” festival at the Library of Congress theater. Experts of all kinds come together to try to identify the films through the smallest details indicating a time or place.

he “Mostly Lost” film festival, which has become a pilgrimage for a subset of movie fans who revere the era long before the advent of computer-enhanced animatronic dinosaurs.

For four years, the event at the State Theatre on the Library of Congress’ Packard Campus has attracted historians with advanced degrees, old men with stacks of even older film tins in their basements and self-taught aficionados who can quickly determine a car’s model year or identify a never-famous actor by the shape of his posterior. This year, an 11-year-old boy, who has appeared on Turner Classic Movies to introduce Charlie Chaplin’s “Modern Times,” missed two days of school to be here.

What they all had in common was an obsession with a time when movies were made without color, sound or social media campaigns.

The Packard Campus, about 90 minutes from Washington, D.C., near the foothills of the Blue Ridge Mountains, houses the largest and most comprehensive film collection in the world.

The 125 films screened over three days in June were mere fragments — five- to 10-minute clips — mostly from movies so obscure that even top film archivists could not decipher the titles, name the actors, or determine the year they were made.

The clue from the 1922 calendar turned out to be a clincher. It matched the film to a publicity photograph — found in an online database called Lantern — from a film called “Small Town Hero,” which involved a woman who works alongside a chimpanzee at a general store. (Chimpanzees show up often in silent movies, as do men in bowler hats.)