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National Library Strategy for Dealing with Cellulose
Acetate in the Collection
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.
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.
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.
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
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:
- Use brief survey results compiled by Angeletta Leggio in
June 2000.
- Ask staff where negatives are known to exist.
- Search the catalogue for references to photographic
materials.
- 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 :
- Overlays - these are deteriorating quite rapidly, and are
currently being copied onto polyester.
- Aerial photographic negatives, including Antarctic
material
- Census material
- Photographic negatives of copies of manuscript or rare
maps
- 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.
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.
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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