Once you have concluded that storage at low temperature is what your collection or parts of your collection need, several options are available depending on your particular situation. First, it is important to underscore that low temperature and low RH have the greatest potential to improve the stability of both old and new films, either nitrate, acetate, or color. In particular, using subfreezing temperature can stabilize acetate film in an advanced state of decay. It is also important to note that while the benefit of RH has its limitation (a minimum of 20% RH is recommended) the potential of low temperature to slow down chemical decay is the greatest, and most importantly, there is no recognized minimum temperature recommendation. Therefore, the coldest possible temperature will always be the best choice in terms of film stability, and essentially, the chosen temperature will for the most part be responsible for the quality of storage you provide to the collection. In the end, controlling RH, or the film moisture content, is more a question of avoiding mechanical damages than controlling chemical decay. To implement such an approach, archivists have a choice between three basic principles. All three can provide proper storage conditions for fast decaying film materials. These options are compared below.
Standing frost-free freezer |
Walk-in cold/frozen vault |
Walk-in cold/frozen vault |
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| Capacity | Typically 15-20 cubic feet. However, for planning purpose consider that only half of the space is usable for storage | Can be customized according to your needs | Can be customized according to your needs |
| Climate control provided by the unit | Temperature only |
Temperature only |
Temperature and Relative Humidity (RH) |
| Temperature | Typically frost-free freezer runs around 0°F (-20°C) Daily defrost cycle involves temporary temperature increase Because of the materials thermal mass temperature increase at the film level is minimum |
Temperature range defined by design |
Temperature range defined by design |
| Relative Humidity (RH) | No RH control inside the unit Wide RH daily cycle Film moisture content must rely on moisture-proof housing |
No RH control inside the unit Film moisture content must rely on moisture-proof housing Passive RH control using moisture buffers (moisture conditioned silica gel) and “sealed” cabinetry have been in use |
Film moisture content is governed by Temp and RH levels maintained in the vault |
| Possible Housing Options | 2 heat-sealed aluminum bags around existing enclosures 2 plastic bags (LDPE) with RH detector around existing enclosures Any other customized moisture-proof systems will work |
2 heat-sealed aluminum bags around existing enclosures 2 plastic bags (LDPE) with RH detector around existing enclosures Any other customized moisture-proof systems will work |
No specific housing requirements Housing providing overhead water protection are preferred
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| Materials Preparation | Prior to being placed inside moisture-proof housing, film materials may have to be moisture pre-conditioned Never seal film during hot and humid conditions. Too much moisture may be trapped inside the sealed packaging Film in equilibrium at 68°F (20°C) and 60% RH maximum can be packaged safely Trapping an excessive amount of moisture inside the sealed packaging can lead to mechanical damage (gelatin softening, blocking) when film is retrieved from storage |
Prior to being placed inside moisture-proof housing, film materials may have to be moisture pre-conditioned Never seal film during hot and humid conditions. Too much moisture may be trapped inside the sealed packaging Film in equilibrium at 68°F (20°C) and 60% RH maximum can be packaged Trapping an excessive amount of moisture inside the sealed packaging can lead to mechanical damage (gelatin softening, blocking) when film is retrieved from storage |
No material preparation is needed Re-housing materials can be done based upon the criteria below Do enclosures provide adequate physical protection, and protect against possible overhead water damage? If not, their replacement should be planned Presence of solid particles from metal corrosion should be an incentive for re-housing At low temperature, replacement of tightly sealed enclosure is less of a priority. Film, however, may not benefit readily from the ambient RH level |
| Moving film into low temperature storage | Once film materials have been sealed inside moisture-proof enclosures there is no need for thermal acclimatization Materials can be placed directly inside the refrigerated unit Thermal equilibration will occur within hours Inside the sealed package RH will actually decrease a bit due to the hygroscopic behavior of film |
Once film materials have been sealed inside moisture-proof enclosures there is no need for thermal acclimatization Materials can be placed directly inside the refrigerated unit Thermal equilibration will occur within hours Inside the sealed package RH will actually decrease a bit due to the hygroscopic behavior of film |
No need for material acclimatization Materials in their common enclosures can be placed directly inside the climate controlled vault Thermal equilibration will occur within hours Moisture equilibration, depending upon the temperature and the type of enclosures, may take from several months to a year |
| Retrieval | Avoid water condensation on the film materials This is easily done because materials are protected by the moisture-proof packaging Materials can be moved directly into a warmer room (e.g., viewing room) Water condensation will occur on the outside of the package Although, thermal equilibration will occur within hours, it is best practice to wait 24 hours, or at least overnight, prior to accessing the film Film moisture content should be the same as it was initially |
Avoid water condensation on the film materials This is easily done because materials are protected by the moisture-proof packaging Materials can be moved directly into a warmer room (e.g., viewing room) Water condensation will occur on the outside of the package Although, thermal equilibration will occur within hours, it is best practice to wait 24 hours, or at least overnight, prior to accessing the film Film moisture content should be the same as it was initially |
Avoid water condensation on the film materials Temporarily placing the film inside a moisture-proof container (plastic tub, cooler, or reclosable plastic bags) while still inside the storage is one option Using a temperature and RH controlled staging room is another. Set points should be such that the dew point temperature should always be below the temperature of the object being moved from one space to another Although, thermal equilibration will occur within hours, it is best practice to wait 24 hours, or at least overnight, prior to accessing the film Depending on the storage environment, film may have to be moisture reconditioned to regain its initial physical properties |
| Key points for decision making | Free-standing freezer provides an efficient, contained low-cost system Best option for storing small quantities of film at subfreezing temperature Moisture-proof housing incurs additional costs Access to materials is somewhat constrained due to limited storage space, and the packaging system which would require seal to be opened This option may not be compatible with the need for frequent access to the collections’ materials As the number of required units increases, the financial benefit decreases. Beyond 10 units this option is not recommended Material preparation prior to storage is labor intensive |
The size of such a vault can be adapted to any need Refrigerated vault (without RH control) incurs lower initial expenses The use of moisture-proof housing, or a combination of cabinetry and moisture adsorbents lead to additional costs Access to materials may be easier Material preparation is labor intensive |
The size of such a vault can be adapted to any need Best option for large collections Ease of access is maximized No extra labor for materials’ preparation prior to storage Initial costs, while rather significant, will be recovered by postponing further decay, and therefore reducing the need for duplication/reformatting to avoid content losses |