The Volatile History of Film
From the birth of cinema in the 1890s until around 1951, virtually all professional 35mm motion pictures were printed on a film base made of cellulose nitrate. This early plastic was prized for its transparency, strength, and flexibility, making it an ideal medium for capturing and projecting images. However, nitrate film possesses two infamous and dangerous characteristics that have had a profound impact on film history and preservation.
Flammability and Decomposition
- Extreme Flammability: Cellulose nitrate is chemically similar to guncotton. It is extraordinarily flammable, capable of burning even when submerged in water, and requires less oxygen than normal fire to combust. This made projection booths incredibly dangerous, and numerous catastrophic theater and vault fires were caused by nitrate film ignition.
- Inevitable Decomposition: Nitrate film is chemically unstable and begins to decompose from the moment it is created. As it ages, it releases nitric acid, which acts as a catalyst for further decay. The film becomes brittle, sticky, and gives off a noxious odor. In its final stages of decay, it can auto-ignite at temperatures as low as 40°C (106°F).
Because of this inherent instability, it is estimated that over 75% of all American silent films, and 50% of all sound films made before 1950, are lost forever. The urgency of transferring surviving nitrate prints to modern, stable ‘safety film’ is the central mission of film archives around the world.