Literally thousands of silent films were made in the years leading through the inroduction of sound, but a considerable number of those films (historians estimate between 80 and 90 percent) have been lost forever. Movies of the first half of the 20th century were filmed on an unstable, highly flamable nitrate film stock, which required careful preservation to keep from decomposing over time. Most of these films were not preserved; over the years, their prints simply crumbled into dust. Many of them were recycled, and a sizable number were destroyed in studio fires. As a result, silent film preservation has been a high priority among movie historians.
Because of the fragility of film stock, proper preservation of film usually involves storing the original prints in climate-controlled storage facilities, preferably ones with decent air circulation and refrigeration. The vast majority of films are not stored in this manner, which has resulted in the widespread decay of film stocks.
The problem of film decay is not limited to silent films. Movie industry researchers and specialists have found that color films (especially ones made in less expensive, less permanent processes than Technicolor) are also decaying at a rapid pace. A number of well-known films only exist as copies of their original master prints, because the originals have become unusable.
"Preservation" of film usually refers to physical storage of the film in a climate-controlled vault, and sometimes to repairing and copying the actual film element. Preservation is different from "Restoration". Restoration is the act of returning the film to a version most faithful to it's inital release to the public and often involves combining various fragments of film elements.
In most cases, when a film is chosen for preservation and/or restoration work, new prints are struck from the original negative or composite restoration negative for general viewing and preservation elements, such as fine grain maser positives and duplicate printing negatives, are generated to make duplication masters available to future generations.
Sometimes (when budgets are lower) the images are transferred to video or digital media for easy transport and copying. Film preservationists would prefer that film images be transferred to other film stock, because conversion from film to a digital image results in a loss of quality that can make it more difficult to create a high-quality print based upon the digital image. (However, digital imaging technology is increasing to the point where the human eye has difficulty perceiving the difference between filmed images and digitally transferred images.)
The cause for film preservation came to the forefront in the late 1980s and early 1990s when such famous and influential film directors as Steven Spielberg and Martin Scorsese contributed to the cause. Spielberg became interested in film preservation when he went to view the original master print of his film Jaws, only to find that it had badly decomposed and deteriorated -- a mere fifteen years after it had been filmed.
The film preservation movement has resulted in a number of classic films being restored to pristine condition. In many cases original footage that had been excised (or censored) from the original print have been re-inserted into the films.
In the age of digital television, HDTV and DVD, film preservation and restoration has taken on commercial as well as historical importance, since audiences demand the highest possible picture quality from digital formats.
A number of "lost" movies have become legends in themselves. These movies were either extraordinarily successful or controversial, but all prints of the original films have been lost because they decayed or were destroyed, and thus they were unable to be preserved. Examples of such "lost" films include Greed, London After Midnight, and even the original master print of Citizen Kane.