The first rule in film preservation is Save the Originals! The original photographic material will always provide the “truest” visual record of events, even if digitally enhanced copies may “look better” in some ways. Fortunately, films do not require elaborate storage solutions to remain viable for many years. Essentially, keep them in a cool but dry environment and house them in containers that allow them to “breathe.”
Firstly, it is best to keep your reels of film in some kind of enclosure so that dust and other environmental substances do not settle on them. These enclosure, however, should not be airtight. The reason is that as acetate film ages, it gives off trace amounts of acetic acid in gaseous form, which is a catalyst to further acetate decay. Therefore if this gas is trapped within a tightly-sealed can, this “autocatalytic” effect will speed the decay of the film. When this happens, you will smell a distinct vinegar odor, and degradation of the film base may soon lead to warping and shrinking of the film, and eventually to disintegration of the image. So, do not use zip-lock bags to store films, as convenient and safe as that might seem. Modern vented cans – or even older ones whose lids easily slide off – are ideal. A show box with a loosely fitting lid can also serve nicely, although you should weigh the possibility of water damage if there are pipes or sprinkler systems nearby.
Outside of a professional archival vault, it will be most natural to store your films in your home, and they will generally be happiest where you are happiest. That is, not stashed in a hot dry attic where the acetate film will tend to dry out and shrink, and not relegated to a garage or basement prone to dampness and cold, where mold will develop and high humidity may hasten “vinegar syndrome.” Films are happiest in a cool, dry environment, protected from high humidity at any temperature.
The National Film PreservationFoundation (NFPF) provides a useful account of Film Decay and How to Slow It on their website, along with links to further preservation resources.