Film emulsion pre-1951 on unstable cellulose nitrate base — highly explosive, shrinks and yellows over time. Archive nightmare; why old films burn.
Anyone dealing with archival material or undertaking restoration will inevitably encounter this material question: cellulose nitrate was the standard for film emulsion until the early 1950s. The stuff is chemically unstable — it shrinks, yellows, develops an acetic acid odor, and can ignite spontaneously. When handling original reels from the 1920s to the 1940s, you are literally holding a safety hazard in your hands.
The problem lies in its molecular structure: cellulose nitrate is highly oxidative and self-accelerating during decomposition. Once the process begins, it speeds itself up — a self-amplifying effect that causes old nitrate film archives to become veritable fire hotspots under unfavorable storage conditions (heat, humidity, poor ventilation). Film museums and archives therefore store nitrate material in special, cooled vaults with monitoring. The reason: a fire is not caused by external ignition — the reels can ignite themselves.
Practically, this means for restoration: nitrate film must be digitized and transferred to stable triacetate or polyester to be preserved long-term at all. The scan itself is not critical as long as the handling temperature remains low. Many classics — silent films, early sound films — only exist as nitrate originals. A large portion of the cinematic heritage of the silent film era has been lost or irreparably decayed because nitrate material is simply not storable. Studios and archives from the 1960s to the 1980s destroyed tons of material or left it to decompose unattended — partly because the operating costs for safe storage were too high.
When cutting nitrate film (if you are still working with originals — rare today), you had to be extremely careful: the material is brittle, splinters easily, and had different running characteristics in the cutting machine compared to acetate. For modern work, nitrate material is irrelevant — all historical sources are transferred to digital or safe triacetate. But for archivists and restorers, it remains a constant challenge: time is running out against chemistry.