Cold Storage
Cold storage (below freezing) or cool storage (above freezing) can greatly slow or halt the rate of deterioration. It is especially useful for color photographs and cellulose nitrate and cellulose acetate films due to the instability of color dyes and plastic supports.
Because the benefits of cold storage are diminished if frequently used items are cycled in and out, it is best suited for low-use collections or those for which reference copies exist. If only a few items in a collection are frequently used, it is best to duplicate them and then place the entire collection in cold storage. Materials should not be removed more than once or twice per year, nor should they be left out of cold storage for long periods of time. Sources differ on the need for vapor-proof packaging which is essentially plastic enclosures that prevent condensation from accumulating on the materials. If the cold storage unit does not have relative humidity control then it is necessary. Even if humidity control exists, it is advisable to use vapor-proof plastic packaging in case of a system failure. Cold storage rooms should be fitted with alarms that are connected to a 24/7 remote monitoring station that alert staff to a failure. While older literature calls for reformatting before items are placed in cold storage, more recent publications indicate that preservation of the originals should take priority. Instead, duplicate prints and slides can be used as reference copies. Heavily used items should be duplicated to create use copies before being placed into cold storage if at all possible. As digitization projects are commenced, photographs can be removed from cold storage.
In order to safely remove items from cold storage, it is necessary for them to slowly acclimatize or warm up before use. If materials are sealed in vapor-proof packages, the packages can be left at room temperature. Items not in packaging should be immediately placed in a plastic bag and allowed to acclimatize outside of cold storage. If the staging area is excessively warm or materials need to leave the building, they may be placed in a Styrofoam cooler. Loose photographs require 30 to 60 minutes to warm up while boxes may take two to four hours depending on size and quantity of photographs. Materials may be removed from their plastic packaging when they no longer feel cool to the touch. |
Materials that greatly benefit from cold storage at temperatures below freezing:
Materials that greatly benefit from cold storage:
Materials that benefit from cool or cold storage at any temperature but are much less vulnerable to deterioration in normal archival conditions:
Materials that should not be frozen:
If these items are frozen, they may crack or break or their chemical structure may be compromised. |