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National Library Strategy for Dealing with Cellulose Acetate in the Collection

Introduction

Principles

Strategies generally applicable

Copying

Strategies applicable to specific collection areas

Resource implications

Decision flowchart


Introduction

Cellulose acetate has been a widely-used carrier for photographic film, motion picture film, sound tapes and microform. The NLA has large holdings of cellulose acetate based items, which form a valuable part of its collections.

Cellulose acetate is known to degrade, and to eventually degrade very rapidly, if stored under suboptimal conditions. Degrading acetate needs to be segregated from film in good condition because degradation products catalyse the deterioration of new or fresh material.

At some point it is likely that all information resources on cellulose acetate will have to be copied to other more stable systems.

The goal of this strategy is:

  • to preserve and safeguard important items in Australia's material heritage collection held at the NLA through storage under conditions which will optimise their survival; and

  • to ensure continued access to information stored on acetate based materials via copying information from degrading acetate carriers.

Principles

The following principles provide the foundation for the proposed strategy for dealing with cellulose acetate (hereafter generally referred to as "acetate") in the Library's collections:

  • The acetate-based material in the Library's collection will be identified, retrieved and assessed in terms of its significance, level of deterioration, and level of use.

  • Material considered to have high significance will be copied, and permanently retained.

  • All material of enduring value found to be on acetate will be placed in cold storage and copied. Material of low significance may be placed in cold storage and only copied if and when requested by a user, if the quantity of material in this category is very large and rarely accessed. Cold storage in this document refers to both cold store (8 ºC) and freezer storage.

  • Every attempt will be made to allow ready access to high use materials. Access may be subject to conditions designed to ensure that the material is not put at risk.

  • Following copying, material earmarked for permanent retention will be placed in permanent freezer storage at -18 ºC. The original material will then be accessible only under exceptional circumstances. Users will be directed to the replacement copy.

  • Material considered to be valuable only for the information it contains will be copied and discarded where acquisition agreements permit.

  • All material will be copied according to preservation standards, and copies will be carefully checked to ensure that these standards have been met. Quality checking will be carried out at the time of copying, and over time to detect deterioration in the new copy.

  • Priorities for copying will take account of comparative significance, condition, and level of use of candidate material. · The program of copying will be undertaken in association with the Library's existing digitisation program where practical. · The condition of acetate material in storage will be periodically monitored.

Strategies generally applicable

To manage its acetate holdings, the Library will have to undertake a range of strategies including identification and retrieval, assessment, storage, copying, and in some cases, disposal.

Identification and Retrieval of Cellulose Acetate

Teams comprising staff from Preservation Services and specific collection areas will be formed in order to locate, retrieve and identify acetate materials.

Staff from collection areas will be responsible for broadly assessing the significance of material likely to include acetate (prior to retrieval in the case of Pictorial and Maps, and following retrieval in the case of Manuscripts). Preservation staff will be responsible for the retrieval of items from storage.

Assessment of base material and condition

Retrieved material will be tested to see if it is acetate-based, using the polarization test. This test involves placing the material between crossed linear polarizing filters, and seeing whether or not birefringence patterns can be observed. This test can be carried out quickly, and gives reliable results suitable to the Library's needs.

The test identifies polyester film. Material found to be not polyester can be assumed to be cellulose acetate, with a small chance that some cellulose nitrate may be encountered. Knowledge of the deterioration characteristics of cellulose nitrate will allow nitrate to be distinguished from acetate.

Cellulose acetate will be assessed for level of deterioration using A-D detector strips. These will be placed into a sealed package containing the material and left for at least 48 hrs. Material found to have an A-D reading of 2 or higher will be considered to be in a deteriorated state. Material with a reading of 1-2 will be considered to be under threat, although not yet seriously degraded.

Preservation staff will be responsible for determining whether the retrieved material is acetate, nitrate or polyester, and assessing its condition.

Storage

Material with an A-D strip reading of 2 or higher has passed the autocatalytic point. It will be placed in a freezer in a vapour-proof enclosure to arrest further deterioration. This material will not be accessible to users until after copying. The Library will purchase a freezer capable of maintaining temperatures of -20 °C, to be located near the LG2 Cold Store. Depending on how much deteriorated material is found, it may become necessary to buy more than one freezer.

Material with an A-D strip reading below 2 has not yet reached the autocatalytic point. This material will be sealed in a polyethylene bag and placed in the Cold Store with silica gel to adsorb moisture and degradation products. Twenty-four hours notice will be required for access, as the material will require acclimatisation to ambient conditions.

Locations of material being cold-stored will be recorded according to existing procedures. Instructions will be posted on the freezer unit detailing acclimatisation procedures.

Teams comprising Preservation staff and staff from the relevant collection area will be responsible for moving material into cold storage and for recording changes in the location of material, in line with existing procedures.

Acclimatisation Procedures

Material placed in cold or freezer storage will require acclimatisation procedures to prevent damage as it passes from one set of environmental conditions to another.

For material going into the freezer:

Photographic material will be sealed in a vapour-tight enclosure at room temperature and low relative humidity. Care will be taken to expel as much air as possible in order to prevent condensation of moisture onto the material as it cools. The item will then be placed inside an esky or similar insulating container prior to being placed in the freezer. This container can be removed after 4-5 days, when the material has equilibrated to the freezer conditions.

For material coming out of the freezer:

On retrieval, material that has been frozen must be allowed to equilibrate to ambient conditions slowly. The material will be insulated and placed in the Cold Store for at least 4 days, and then allowed to equilibrate to room temperature for at least 48 hours, within its sealed and insulated enclosure. The sealing is necessary to ensure that the moisture content of the material is kept constant as the temperature changes.

For material going into the Cold Store:

Material going into the Cold Store will first be placed in the acclimatisation room. After a week, the material will be placed inside a polyethylene bag with silica gel, and the package sealed. Commercially available freezer bags would be suitable for this purpose.

For material coming out of the Cold Store:

Material to be retrieved will be removed from the Cold Store and allowed to equilibrate to ambient conditions in the acclimatisation room while remaining sealed.

Copying

The Library is fortunate in that there are already copying programs in place that either have or will address much of the cellulose acetate material of long term value. The Library has been investing in duplicating its at-risk microfilm holdings and audio collections for some years, and the Library's digitisation programs are likely to cover most acetate Pictorial material over the next few years.

To develop copying programs specifically addressing acetate should only require some attention to priorities in these existing programs, as well as some other relatively modest new programs.

To coordinate acetate copying, teams comprising staff from Preservation Services and relevant collection areas will be formed. Where appropriate, these teams will work in association with the Library's digitisation team.

Because the copying program for acetate material must produce replacement copies for long-term retention, quality control issues will be critical. Procedures for specifying and checking quality will form an integral part of the copying process.

It is proposed that priorities for copying acetate materials be based on value, its level of deterioration and its level of use. The following table summarises a proposed classification scheme and order of copying priorities:

Value of Material High Significance Medium Significance Low Significance
Level of Degradation High Low High Low High Low
High/Low use High Low High Low High Low High Low High Low High Low
Priority for copying 1 2 4 5 2 3 5 6 3 4 6 7

Table 1: Determining priorities for copying

Strategies applicable to specific collection areas

Manuscripts

The Manuscripts Collections contain considerable cellulose acetate in the form of microforms, which may include service copies of material from other sources. These service copies will be treated as masters in situations where the location and/or condition of the original material is unknown. The collections also include some photographic negatives and audio recordings likely to include some acetate material.

Microform held in Manuscripts includes important AJCP material. The Library has an ongoing program of copying any acetate AJCP material to polyester film. This program will need to continue for some years at current resource levels in order to complete the task.

Compared with other parts of the Library, the amount of cellulose acetate in Manuscripts is relatively small, but dispersed and therefore not immediately and easily accessible. It is as yet unclear how much material there is, and priorities cannot be assigned prior to locating the material.

It is suggested that material be located using leads as follows:

  1. Use brief survey results compiled by Angeletta Leggio in June 2000.
  2. Ask staff where negatives are known to exist.
  3. Search the catalogue for references to photographic materials.
  4. Manually search through finding aids for the terms 'negative' under the 'scope and contents' portion of the entry.

On a long-term basis, users could also be asked to report any photographic negatives they come across.

The location of any audio materials found in the course of looking for acetate will be noted. (A sound preservation project is currently underway to find and process audio and digital materials currently located in Manuscripts.)

Maps

The Map collections contain five categories of material likely to include some cellulose acetate. In descending order of significance, these are :

  1. Overlays - these are deteriorating quite rapidly, and are currently being copied onto polyester.
  2. Aerial photographic negatives, including Antarctic material
  3. Census material
  4. Photographic negatives of copies of manuscript or rare maps
  5. Microforms

The microforms are in the highest use category.

It is estimated that locating material and testing to see if it is acetate will take four person weeks. It is suggested that the first step should be to identify priority material based on significance, prior to searching for acetate amongst those priority groups.

Microform Service Copy collection

There are a large number of service copies of microform held by the Library which may be acetate. While their status as service copies suggests they should not be of preservation concern, their importance to the Library is often complicated by difficulties in finding where the preservation masters are held, and even whether they still exist.

A simple exercise of identifying which material is acetate-based, and arranging for it to be copied, is inappropriate for this collection. On the other hand, the loss of this material would be significant issue for the Library's users.

It is recommended that the issues in ensuring the Library can replace service copies of significant microform collections should be the subject of a separate project.

Music collection

The Music collection contains sound recordings that may be on cellulose acetate. This material is currently located in the Nmt run and in specific sections in the Music collection. Sound Preservation will approach Music to formalise procedures for identifying and forwarding sound recordings to SPATS for optimal storage and preservation copying.

Oral History collections

The Oral History collections contain many reel-to-reel tapes on acetate base. This material is adequately documented on the Sound Preservation Database, and is already given priority for preservation attention. No additional strategies are needed.

Pictorial Collections

The Pictorial Collections contain a large quantity of acetate material, mostly consisting of negatives. Some of this material has already been prioritised for digitisation in 2001/2002.

It is estimated that it would take one full-time person up to 3 months to locate all the cellulose acetate within the collection.

The attached flowchart illustrates the process which will be followed.

Resource Implications

It is estimated that it will be necessary to recruit the equivalent of one full-time person at APS 3 level for a period of 18 months to carry out the location, retrieval, identification, assessment (using the polarization test) and storage of cellulose acetate for the Library's collections.

The Library will need to purchase freezers to store deteriorated cellulose acetate prior to copying. A storage area, close to the Cold Store will need to be identified to house these freezers. Packaging supplies will be needed to house materials. Long-term freezer storage (possibly off-site) will also need to be obtained.

While it is difficult at this stage to estimate the funds required for copying, substantial additional funding will be required over the next 10 years to digitise, or copy to polyester, all cellulose acetate identified. Following the completion of the identification of cellulose acetate in the Library's collections, a clearer budget estimate will be possible. It is anticipated that most of the material of high significance will be copied under the Library's existing digitisation program.

While copying is in progress, resources for monitoring the condition of material in cold storage will be required.

Resource implications for collection areas will include: participation in location/retrieval/identification teams, principally to provide information about the significance of material; participation in copying and storage teams; altered retrieval procedures.

Decision flowchart

This flowchart aims to help collection managers make decisions about their collections, and which storage option should be followed for each material type.

For more information about the work at the National Library of Australia, contact:

Mr Colin Webb
Director, Preservation Services Branch
National Library of Australia
Canberra ACT 2600
Telephone: +61 (0)2 6262 1662
Facsimile: +61 (0)2 6273 4535
Email: cwebb@nla.gov.au
www.nla.gov.au


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