In the early 1990s the use of micro-environmental approaches was investigated in an attempt to further postpone the deterioration of acetate materials. The basic idea was to create a moisture-controlled microenvironment surrounding the film as an alternative to controlling temperature and RH in the whole storage area. This can be achieved by adding moisture-adsorbents, acid-scavengers (e.g., molecular sieves) to adsorb deterioration-by-products (e.g., acetic acid), or by moisture-preconditioning the film prior to storage inside a sealed enclosure. Adsorbents such as silica gel and molecular sieves have been tested, as well as conditioning the film at low RH. Although a macro-environmental approach is generally favored, the use of sealed micro-environments can still have its place in preserving film in certain situations. Facts and guidance are summarized below.
Sealed micro-environments |
Macro-environment |
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| Initial moisture conditioning at low RH (20%) | Use of adsorbents (e.g., molecular sieves) |
Temperature and humidity control | |
| Suitability | May be practical for small collections only, or portions of large collections | May be practical for small collections only, or portions of large collections | For large collections, it is the most practical option |
| Requirements | RH-controlled walkin space for moisture pre-conditioning Sealed housing (e.g., closable bag inside or outside the film enclosure, aluminum tape) Time and effort (labor intensive) |
Molecular sieves packets Sealed housing (e.g., closable bag inside or outside the film enclosure, aluminum tape,…) Periodic replacement of the molecular sieves Time and effort (labor intensive) |
Film moisture content will be governed by temperature and RH levels maintained in the storage environment No added labor to prepare film prior to storage |
| Effect on acetate decay at room temperature (68°F) | Life span can be improved by a factor of 3 to 4 if film is conditioned to 20% RH as compared to 50% RH Stability benefits come solely from lowering film moisture content |
By using molecular sieves (5 wt. %) life span can be improved by a factor of 3 to 4 Supplier recommendations: 2 wt.% Stability benefits come mostly from lowering film moisture content |
At room temperature factor of improvement will be similar to those obtained through micro-environmental approaches |
| Effect of low storage temperature | Storing the sealed materials at low temperature will drastically extend the life span of film Film stability benefits come mostly from low storage temperature, and to a lesser extent from the reduced film moisture content Estimate the stability benefits using the Storage Calculator for Acetate and the Storage Calculator for Color (available in Recommendations when logged in). |
Storing the sealed materials in presence of adsorbents at low temperature will drastically extend the life span of film Film stability benefits come mostly from low storage temperature, to a lesser extent from the reduced film moisture content, and even less from the “capture” of degradation -by-products (e.g., acetic acid) |
Low temperature has the greatest potential to maximize film life span To estimate the effect of temperature and RH on fresh acetate, degrading acetate, and color dyes use the Storage Calculator for Acetate and the Storage Calculator for Color (available in Recommendations when logged in). |
| Ease of access to film | Film micro-environment will be disrupted by accessing the materials Preparation procedure will need to be repeated after accessing materials |
Micro-environment will be disrupted by accessing the materials Adsorbents will need to be replaced |
No extra labor should be required |
| Key points for decision making | Viable option for small collections, or for situations where adverse RH levels cannot not be controlled Place sealed materials at subfreezing temperature to maximize film stability Efficient option to minimize the risk of contamination Will entail added labor and the need for a space providing at least temporarily a low RH level For reference, moisture conditioning may require several weeks during which materials should be exposed to low RH without enclosure |
Viable option for small collections, or for situations where adverse RH levels cannot not be controlled Place sealed materials with adsorbents at subfreezing temperature to maximize film stability Efficient option to minimize the risk of contamination Will entail added labor initially and periodically to replace adsorbents |
Most practical option to provide proper storage environment to large film collections Use low temperature to maximize life span of film while maintaining RH between 20-50% No need for “extra” preparation of materials When storing degrading acetate, air quality should be monitored, and controlled as needed to minimize the risk of contamination |