Film preservation, or film restoration, describes a series of ongoing efforts among film historians, archivists, museums, cinematheques, and non-profit organizations to rescue decaying film stock and preserve the images they contain. In the widest sense, preservation assures that a movie will continue to exist in as close to its original form as possible. For many years the term "preservation" was synonymous with "duplication" of film. The goal of a preservationist was to create a durable copy without any significant loss of quality. In more modern terms, film preservation includes the concepts of handling, duplication, storage, and access. The archivist seeks to protect the film and share its content with the public. Film preservation is not to be confused with film revisionism, in which long-completed films are modified with the insertion of outtakes or new musical scores, the addition of sound effects, black-and-white film being colorized, older soundtracks converted to Dolby stereo, or minor edits and other cosmetic changes being made. By the 1980s, it was becoming apparent that the collections of motion picture heritage were at risk of becoming lost. Not only was the preservation of nitrate film an ongoing problem, but it was then discovered that safety film, used as a replacement for the more volatile nitrate stock, was beginning to be affected by a unique form of decay known as "vinegar syndrome", and color film manufactured, in particular, by Eastman Kodak, was found to be at risk of fading. At that time, the best-known solution was to duplicate the original film onto a more secure medium. A common estimate is that 90 percent of all American silent films made before 1920 and 50 percent of American sound films made before 1950 are lost films. Although institutional practices of film preservation date back to the 1930s, the field received an official status only in 1980, when UNESCO recognized "moving images" as an integral part of the world's cultural heritage. The problem of film decay The great majority of films made in the silent era are now considered to be lost forever. Movies of the first half of the 20th century were filmed on an unstable, highly flammable cellulose nitrate film base, which required careful storage to slow its inevitable process of decomposition over time. Most films made on nitrate stock were not preserved; over the years, their negatives and prints crumbled into powder or dust. Many of them were