Volume 19, Number 4
Sep 1995

Cost-Benefit Analysis for B/W Acetate: Cool/Cold Storage vs. Duplication

This paper has been revised and condensed for publication in the Abbey Newsletter. It was originally given at the March 1994 National Archives Annual Preservation Conference, "Cellulose Acetate Films: Magnitude and Nature of the Preservation Concerns."

Generally, the preservation of black and white acetate film collections will require an approach that combines the use of cool/cold storage, to extend the usable life of original acetate film materials, with systematic duplication onto polyester based film. Often it is hard for collections managers to weigh the relative benefits and costs of an improved storage environment against those of duplication.

Institutions should perform a cost-benefit analysis to determine the most cost-effective approach or combination of approaches to preserve their holdings or collections of acetate film based photographic materials. Cost-benefit analyses can be conducted for specific collections or for an entire institution. Also, a cost-benefit analysis can be used to compare the cost of storage at current environmental conditions, and the corresponding life expectancy of the acetate film at those conditions, to storage at colder temperatures which will provide a longer life expectancy for the film. Generally, for small collections it will be most economical to duplicate the collections, while large acetate film collections will require a combined approach of cool/cold storage and a long-term plan for duplication.

The intent of this article is to provide basic guidance for deciding how best to approach the preservation of photographic film collections. The intent is to provide a framework that can be used to conduct a cost-benefit analysis comparing duplication with cool/cold storage. The same basic approach to cost-benefit analysis can be applied to other preservation management issues.

Duplication Considerations

Duplication is an essential part of any preservation plan for collections of photographic materials. One has to implement long-term duplication projects using available resources. Usually, resources will be limited and most duplication projects will be long-term.

Duplicate only those materials that truly warrant duplication, evaluate collections/holdings, and prioritize materials to be duplicated. The selection and planning for duplication should be based on three priorities: high value, presence of active deterioration, and frequent use. Select the most economical method of duplication that meets all archival/technical requirements, including value of originals, quantity of materials to be duplicated, condition of materials to be duplicated, and the level of use/access required for the materials.

Use polyester based duplicating film for all applications, including motion pictures. Polyester based duplicates are important to reduce the need for cool/cold storage. Polyester film is significantly more stable than acetate film, even at higher storage temperatures. Maintenance of a collection on acetate based film will always cost more for storage because of the need for cool/cold storage.

Costs

Generic duplication and storage costs given here are based on price quotations from vendors and are provided for various photographic formats. Since the cost analyses listed here do not take inflation into account, an inflationary factor should be added to the formula for more accurate estimates. The generic estimates should be used for an initial analysis only. Pricing specific to a particular collection or institution should be used for more accurate analyses.

The cost to duplicate a collection included the actual cost to duplicate each item, the cost to inspect the duplicates, and the cost to store the originals while they are being duplicated.

The cost for inspection can be estimated by multiplying an hourly rate by the approximate time to inspect the material by the number of items to be inspected. To minimize the cost it is recommended that a technical inspection be conducted on a random sampling of up to 10% of the duplicates. Some materials, like legal records on microfilm, may require a comprehensive inspection and 100% verification. Use the following time estimates for inspections.

The cost to store a collection at a specified set of environmental conditions included the cost to build or lease a vault at the desired environmental conditions and the energy costs to run the vault at those conditions.

The first step in determining the cost for storage is to estimate the volume of storage space required. The following estimated storage volumes for selected formats can be used by multiplying the number in the chart by the quantity of negatives/rolls in a collection.

Next the following generic estimates of the cost per cubic foot of material stored per year can be used to determine the storage cost for the estimated volume of material. Multiply the cubic footage of materials by the cost in the following chart.

Now multiply the cost per year by the number of years needed to store the film. This lets you estimate the cost to store materials while they are being duplicated, or the cost to store the materials to reach their life expectancy at specific environmental conditions.

Life Expectancy for Acetate Film

The IPI Storage Guide to Acetate Film can be used to estimate the life expectancy of acetate film materials. The following chart illustrates the predicted life expectancies for the previously cited storage conditions. The first number of years in each storage condition is for new film and the second is for film that has begun to deteriorate.

With all this information it is possible to estimate the cost to duplicate a collection, compare it to the cost for storing the collection for a specific number of years (years to duplicate, years to reach life expectancy, etc.) and estimate the life expectancy of acetate film materials stored at a specific environmental conditions.

Examples

The following are two examples of cost-benefit analyses, one for deteriorating microfilm and one for deteriorating still photo negatives.

The first example is 6400 rolls of 35mm microfilm that show the initial signs of deterioration. The estimated cost to duplicate the 6400 rolls is $63,780 or $152,240. The lower price is for a simple technical quality inspection of the duplicate microfilm, and the higher estimate includes a frame-by-frame verification of every roll of duplicate microfilm. The 6400 rolls could be stored for approximately 40 years (the estimated life expectancy at the following conditions for film in the initial stages of deterioration) at 55°F and 30% RH, for an estimated cost of $33,600. The estimated life expectancy can be increased to 140 years by storing the 6400 rolls at 40&$176;F and 35% RH for an estimated cost of $313,600. In this example it is probably most practical and economical to duplicate all of the film. The theoretical life expectancy of the new polyester based duplicates is 500 years.

The second example is 3 million still photo negatives, a small percentage of which show the initial signs of deterioration. The estimated cost to duplicate all 3 million negatives by contact printing is $39.9 million, including $2.4 million to store the originals at conditions that will extend their life expectancy to the 75 years it will take to complete the project. An alternative approach would be to use a large format, long-roll camera system to duplicate the negatives. The estimated cost of this approach would be $15.4 million and it would take approximately 30 years to complete the duplication; this includes $360,000 to store the originals while they are being duplicated.

Obviously, when a collection is this large, improved storage to extend the usable life of the acetate film negatives is essential to complete the project. The project could be completed in a shorter period of time, but it would require significantly more money and staff to do this. Storing the film at 55°F and 30% RH will provide an estimated life expectancy of 40 years at an estimated cost of $480,000; storing the film at 40°F and 35% RH will provide an estimated life expectancy of 140 years at an estimated cost of $4.48 million; and storing the film at 20°F and 30% RH will provide an estimated life expectancy of 400 years at an estimated cost of $24.3 million. For this size collection, storage at 40°F and 35% RH for 140 years is significantly less expensive than either duplication option and it could be combined with prioritized duplication of only the actively deteriorating negatives, the negatives that are of high value, and the negatives that are requested frequently.

Acknowledgments

Thank you to Sarah Wagner, Photograph Conservator, National Archives, for all the input and editorial assistance. Thank you to Paul Zimmerman, Harris Environmental Systems, to Carl Krotine, Environmental Growth Chamber, to Andy Shelter, Cargocaire Engineering, and to Jill Anderson, Norlake, Inc. for pricing and information on cool/cold storage vaults. Thank you to Anthony Fantozzi, National Archives, to Ed McCarter, National Archives, and to Donna Collins, Library of Congress, for all the information and assistance provided. Thank you to Henry Wilhelm, Wilhelm Imaging Research, and the Image Permanence Institute for all of the information they have published on the stability of photographic materials that was used in creating this cost-benefit analysis system. The complete cost-benefit analysis, with all forms and information, has been published in Topics in Photographic Preservation, Vol. 6, Photographic Materials Group, American Institute for Conservation, 1995.