The University of Arizona
 

Cold Storage of Historic Cellulose Nitrate Negatives at the Arizona State Museum

The Arizona State Museum Photographic Collections include about 15,000 cellulose nitrate negatives from 1910–1950s.

Former storage conditions for cellulose nitrate negativesFormer storage conditions

Former storage conditions for cellulose nitrate negatives at the Arizona State Museum Photo Collections.

Nitrate negatives deteriorate at unpredictable rate over time, giving off nitric oxide and nitrogen dioxide, which is harmful to human health. Gasses that are emitted by deteriorating nitrate negatives can cause damage to artifacts stored nearby. Paper exposed to acidic fumes becomes discolored and brittle and metals undergo a corrosion process. Moreover, nitrate negatives present a severe fire hazard—they are highly flammable and can burn under water. The burning process produces lethal toxic gases. For these reasons, cellulose nitrate negatives have to be isolated from other types of collections and stored below room temperature.

The NEH Preservation and Access Grant provided funding for re-housing of about 7,800 nitrate negatives. Currently, over 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-housingThe sealed box is ready to be loaded into the exposion-proof freezer

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 came 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 of moisture.  Luckily, this was not difficult to achieve in our dry Arizona climate.

Volunteer working on the nitrate negative re-housing project

Conservation student volunteer Jennifer Evers working on the nitrate negatives re-housing project

The project could not have been completed without the help of many staff members and volunteers from Photo Collections and the Preservation Division.