Baby, It's Cold Inside: Freezing Film for Long-term Preservation
In 2011 the Missouri History Museum installed a state-of-the-art freezer for long-term preservation of deteriorating nitrate and acetate films and still photography. Over time, old film bases begin to decay. Nitrate film causes one set of problems, acetate another, but both sets of problems can be resolved by proper preservation assessment and cold storage. Frozen storage halts the deterioration process for both film base types, giving us decades in which to find funding to perform further preservation and duplication of these relics.
The process begins with a “triage” inspection of a film collection. One of the first steps is the acid detection strip test, which tells us how much acetic acid is off-gassing from the film, also known as vinegar syndrome. The off-gassing correlates directly to the amount of deterioration the film has experienced. The films in the worst condition were usually stored in less than optimum conditions and have been exposed to high heat and humidity.
Depending on the inspections, we classify films into three groups. In the worst cases the “patient” is too decomposed for us to ever recover either image or sound, so it is documented as thoroughly as possible and scheduled for deaccession and appropriate disposal. In the best cases the “patient” is in good condition, so we make it comfortable in a new archival film can, document it, and store it in our film vault at about 64 degrees F and with 45% relative humidity.
The films that fall between best and worst are candidates for freezer storage. These films usually have high subject value and have not degraded to the point where images or sound cannot be recovered. They are put through a secondary inspection in which the film is more thoroughly identified, documented, cleaned, and repaired. It is also wound onto an archival film core and stored in an archival film can. Then it is bagged, labeled, and placed in the freezer at 35.6 degrees F and 30% relative humidity. Humidity control is part of what makes the Museum's film freezer “state-of-the-art.” Outstanding air circulation and moveable, compressed shelving also contribute to the excellence of this large, dynamic appliance.
Earlier this year, Museum staff began loading the freezer with the first 200 cans of film, which have been through both the triage and secondary inspections. These films have been on a very long journey, from their beginnings in their poor-quality original film containers, jumbled together without order, to their new, tidy home, properly bagged and tagged in the Museum's freezer.
—Klara Foeller, Curator of Moving Image & Sound Collections