Cold Storage of Historic Cellulose Nitrate Negatives at ASM
A National Endowment for the Humanities Preservation and Access Grant of just under $5,000 provided funding for the re-housing of about 7,800 highly volitile nitrate negatives. ASM's photographic collections include about 15,000 cellulose nitrate negatives dating from 1910 to the 1950s.
Former storage conditions for cellulose nitrate negatives at the Arizona State Museum Photo Collections.
Nitrate negatives deteriorate at unpredictable rates over time, giving off nitric oxide and nitrogen dioxide, which are harmful to human health. The gasses emitted by deteriorating nitrate negatives also can cause damage to artifacts stored nearby. Paper exposed to the acidic fumes becomes discolored and brittle, and metals undergo a corrosion process. Moreover, nitrate negatives present a severe fire hazard as they can even burn under water. The burning process, too, produces lethal toxic gases. For these reasons, cellulose nitrate negatives have to be isolated from other types of collections and stored below room temperature in order to be kept stable..
Currently, more than 5,000 nitrate negatives have been re-housed in a new explosion-proof freezer purchased with grant funds. A range of conservation-grade materials were obtained to ensure optimal storage conditions.
New storage conditions after re-housing. The sealed box is ready to be loaded into the explosion-proof freezer.
Each negative was inserted into a polyethylene sleeve. The sleeves were then placed into a zip-locked bag to keep out moisture and the bag was sandwiched between two pieces of archival buffer board. The package was loaded into a labeled, archival quality cardboard box and then sealed into another zip-locked bag. Each box is equipped with a relative humidity indicator attached to the side, making it easy to monitor humidity levels inside. It is important to make sure that the relative humidity inside the box does not rise above 35% in order to avoid condensation. Luckily, this was not difficult to achieve in our dry Arizona climate.
Conservation student volunteer Jennifer Evers working on the nitrate negatives re-housing project
This project could not have been completed without the help of many staff members and volunteers from Photo Collections and the Preservation Division.
Photos by ASM Staff
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