Film base material—stable until archive heat/humidity spike. Prone to vinegar syndrome in poor storage. Rarely shot on anymore.
You will still encounter acetate films in archives or when purchasing remaining stock—this material was the standard for 16mm and 35mm film rolls for a long time before polyester arrived. The chemistry behind it: cellulose treated with acetic acid to make it more durable than the highly flammable nitrocellulose material of the silent film era. Sounds robust, but it's only so under ideal conditions. The most important thing: acetate ages actively. With improper storage—too warm, too humid, insufficient ventilation—the material begins to release acetic acid. You'll smell it immediately: that typical vinegar odor is not a good sign, but the beginning of the end. This is called vinegar syndrome, and it is irreversible. The film becomes brittle, the emulsion sticks together, and the stock is then practically useless.
On set itself, acetate played a subordinate role for a long time—it was archival material, stock film, or leftover inventory. You deal with it when you have old negatives digitized or work in a film library with existing rolls. Storage is critical here: stable at 13–16 °C, under 30% relative humidity, in metal cans with silica gel packs. Many archives neglected this in the past, which is why a large portion of acetate stock is endangered today. Digital scans are the only salvation here before vinegar syndrome strikes completely.
Practically speaking: do you still buy acetate film today? No. Polyester-based bases (polyester is the modern standard) are more stable, durable, and not susceptible to this chemical decomposition. But if you're dealing with older material—whether for restoration, archival work, or digitization—you need to know the problems. Even a few degrees too much or too much humidity accelerate the process by years. Therefore: don't just store old rolls, but inspect them and—if necessary—digitize them quickly before the material itself becomes a problem case.