The most serious problems originate from deterioration of plastic film support. Most preservationists are familiar with nitrate film decomposition. As nitrate film decays, it can become highly flammable at relatively low temperatures. The rusting is caused by acid gases emitted by the degrading nitrate film.
Good storage can keep even nitrate film from deteriorating.
This original negative of the 1903 classic, The Great Train Robbery, has been stored in the vaults of the Library of Congress. The original nitrate negative of Edison's 1903 classic, The Great Train Robbery, is in excellent condition, residing happily in cool storage in the Library of Congress film vault.