For example, the 1922 film Sherlock Holmes was eventually discovered but some of the footage is still missing.
Much depends on the environment in which it is stored.
Ideal conditions of low temperature, low humidity, and adequate ventilation can preserve nitrate film for centuries, but in practice the storage conditions were usually far from ideal.
When a film on nitrate base is said to have been "preserved", this almost always means simply that it has been copied onto safety film or, more recently, digitized; both methods result in some loss of quality.
In some cases, such as London After Midnight, the surviving coverage is so extensive that an entire lost film can be reconstructed scene by scene in the form of still photographs.
Stills have been used to stand in for missing footage when making new preservation prints of partially lost films.
Most lost films are from the silent film and early talkie era, from about 1894 to 1930.The largest cause of silent film loss was intentional destruction, as silent films were perceived as having little or no commercial value after the end of the silent era by 1930. Harris has said, "Most of the early films did not survive because of wholesale junking by the studios. They simply needed vault space and the materials were expensive to house." Many other early motion pictures are lost because the nitrate film used for nearly all 35 mm negatives and prints made before 1952 is highly flammable.When in very badly deteriorated condition and improperly stored (e.g., in a sun-baked shed), nitrate film can even spontaneously combust. For example, a storage vault fire in 1937 destroyed all the original negatives of Fox Pictures' pre-1935 films.A 1967 MGM vault fire resulted in the loss of hundreds more silent films and early talkies.Nitrate film is chemically unstable and over time can decay into a sticky mass or a powder akin to gunpowder.This process can be very unpredictable: some nitrate film from the 1890s is still in good condition today, while some much later nitrate had to be scrapped as unsalvageable when it was barely twenty years old.