Plastic base of all classical film stock until ~1990s — flammable, chemically unstable, but the standard. Archive and restoration only now.
Anyone working with archive material or digitizing old film reels will inevitably encounter cellulose acetate – this stuff was the backbone of analog production for decades. The plastic base made mass production of 35mm, 16mm, and Super 8 strips possible because it was flexible enough to run through cameras and editing tables, yet stable enough to last for decades – at least theoretically.
The Chemical Problem: Cellulose acetate is a polyester that decomposes under unfavorable conditions. Storing old reels in heat and high humidity dramatically accelerates degradation. The characteristic acidic smell – often described as "vinegar smell" – is the warning sign: the acetate groups split off, acetic acid is produced, and the process becomes self-perpetuating. Some archives report reels turning from clear to a milky haze within a few years. This is irreversible. Therefore, original reels are stored in climate-controlled rooms – ideally 16 °C, 30% relative humidity – and digitized prophylactically.
Handling During Cutting and Digitizing: Acetate film can be cut more cleanly than modern polyester formats (which were introduced later), but the splices become brittle with age. Handling it isn't about reverence, but pragmatism: aged film tears more easily, attracts dust, and can cause scratches in the scanner. Some digitizers spool old reels slowly multiple times before the actual transfer to stabilize the structure. Others work with special cleaning solutions, which also carry risks.
The Break with Today: Modern film strips use polyester (polyethylene terephthalate) as a base – chemically more stable, less odorous, but less sentimental. In practical work, cellulose acetate today only plays a role in archive restoration. Anyone who still occasionally encounters it – in collections, found footage projects, or documentaries about film history – should know: the material is not eternal. Digitization is not optional; it is emergency medicine.