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Deterioration of Photographic Materials
Photography can be defined as any method
producing a visible image by the inter-action of light with a
layer of chemicals. Since the birth of still photography in 1839,
photographs have been manufactured employing many different methods.
About 40 of these methods have been used commercially and examples
of the resulting images can now be found in great numbers and
varieties in archives and library collections.
The development of a commercially successful
system for recording and viewing moving images was the result
of work by many people in the latter part of the 19th century.
The first successful public demonstrations were given by Lumi_re
in Paris in 1895. Since then many advances have been made including
the introduction of sound and of colour. Many different frame
rates and sizes of film were devised before the industry stabilised
on to a few "standard" formats. A film collection still
has to be able to handle films on many formats.
Microfilm was developed to secure original
print and image material with special historical, commercial or
scientific value. The use of microfilms can also improve the access
to the information carried by the original documents. The use
of microfilm for access will, as with other forms of access copy,
help preserve the original by protecting it from wear and tear
and from theft.
The most recent developments are as a
result of the computer revolution. New techniques have been developed
using equipment such as ink-jet and thermal sublimation printers
to produce copies of digitised images. These should be considered
as printing techniques and not as photographic materials although
they can provide a good representation of the original photographic
image. Because of the short life expectancy and the sensitivity
to light and heat, these printing techniques cannot be considered
a substitute for photographic materials.
The best practice for photographic materials
is to have several sets of images:
The Original Image kept in ideal conditions and disturbed as infrequently as possible.
A Safety Master used as a reserve copy. It should be stored in a separate place to the original in case of the loss of the original in a fire or some other disaster and also kept in good storage conditions.
A User Copy Master made from the original or the safety master and used to make User Copies.
User Copies
for routine access to the images.
Though photographic images have been
made in a great number of different sizes - from microfilms to
large posters - the deterioration and preservation principles
are dependent upon the chemical process used to make the image
and not the size or purpose of the image. As the production of
photographs has included many different chemical processes in
the capture of the image, photographs also have a wide variety
of ageing properties. Some materials were made of extremely selfdestructive
components, others were very sensitive to physical contact and
almost every photographic material is sensitive to the environment,
not only temperature, relative humidity and air pollution but
also oxidising substances found in emissions from some building
materials, wall paints and wooden furnishing. The cardboard
and paper in boxes and envelopes used for protecting the items
from physical damage may also contain harmful substances.
Deterioration Factors
Deterioration factors can be categorised
in two ways internal and external.
1. Internal Deterioration
Internal deterioration factors are dependent
on the components of a photographic item and the residual chemicals
from developing and post treatment processes. The speed
of the decay processes is related to relative humidity, temperature
and oxidising substances.
The most commonly known example of a
photographic material deteriorating from internal processes is
cellulose nitrate film, which during deterioration emits substances
that both accelerate the deterioration process as well as attacking
materials in the vicinity.
Another materials group exposed to self
destruction is that of acetate film the first safety film.
Until recently, acetate film was considered as very stable but
today the problem of the Vinegar Syndrome the popular name
for the deterioration of acetate film with the emission of acetic
acid (vinegar) vapour as a by-product that acts to accelerate
the rate of decay is widely known. Still another example,
although involving an old process, is the yellowing of albumen
prints, where the egg white in the emulsion bleaches the silver
image.
Colour photographs - negatives, prints
and transparencies - generally have bad ageing properties as
the colourcomponents are unstable unless kept below 0°C.
Photographic colour materials are not only subject to light fading
- fading of the colours and image in the presence of light - but
also to dark fading - fading in the absence of light. Transparencies
are commonly considered to have better colour stability than colour
negatives and prints but ageing properties may differ greatly
due to different chemical properties.
A Few Examples
Collodion, one of the earliest photographic
emulsion materials, was used in several similar photographic
techniques during the midl8th century, e.g. ambrotypes,
collodion wet plates, pannotypes, ferrotypes and celloidin paper.
The collodion emulsion contains cellulose nitrate (also used for
the first "plastictype" film base) and emits nitrous
gases, though far less than cellulose nitrate film. These gases
may attack other objects in the vicinity and, due to the loss
of gas which leads to shrinkage of the emulsion, the emulsion
may eventually crack.
Supports that are subject to self-deterioration
include cellulose nitrate film, acetate film and some of the modern
resin coated or so called plastic paper. The main ingredient of
nitrate film is cellulose nitrate which emits nitrous gases. The
gases are not only oxidative but also toxic and explosive. In
a selfaccelerating deterioration process, the support
the film base and the emulsion are eventually completely
destroyed. What is left is a sticky substance. Cellulose nitrate
film is flammable at fairly low temperatures and rolls of film,
like motion picture films, might even self ignite at a room temperature
as low as 41°C
when kept for an extended period of time in a badly ventilated
environment, for example in the traditional metal film can. Cellulose
nitrate film sheets do not self ignite in the same way because
the mass per volume is much less and normally the emitted gases
slowly evaporate away from the negatives when they are kept in
envelopes and open boxes.
Acetate film was introduced in the l920s
as a substitute for the flammable cellulose nitrate film. It was
labelled "safety film" as it was less flammable than
its predecessor. The early acetate film lacked dimensional stability
which made it shrink and loosen the emulsion from the support.
The acetate base was improved and was considered more or less
stable until the vinegar syndrome was discovered during last decade.
PE or Resin Coated papers are made from
paper fibres covered with polyethylene with the gelatine emulsion
outside the polyethylene layer. Until about the mid 1980s this
photographic print paper had bad ageing characteristics. The paper
base contained optical whiteners which absorbed light energy.
An oxidising substance was formed which attacked the resin coating
resulting in cracking. The oxidant also attacked the silver image
and bleached it. During the last decade an antioxidant has
been introduced and thus the resin coated papers now have improved
longevity.
Microfilms have been and are produced
using a variety of processes but the silver-gelatine developing-out
film is considered to have the best long-term stability. Diazo-
and vesicular processes are commonly used for making access copies
but they do not have long-term stability and are not recommended
for preservation copies.
2. External Deterioration Factors
External deterioration factors are harmful
substances in the preservation environment. Among the many contaminants,
a few should be particularly mentioned. Lignin, alum rosin sizing
and oxidative residual chemicals in paper and cardboard used for
envelopes, boxes and mounting boards as well as plasticisers in
PVCfolders and similar storage media are the most common
together with air pollutants. Furbishing in repositories should
not consist of materials emitting oxidising gases. Oxidising gases
react with photographic materials in a similar way as common air
pollutants. High temperature and relative humidity accelerates
these processes.
Synergetic Effects of Internal and
External Deterioration Factors
The external deterioration factors may
cooperate with the internal factors to increase the reaction
speed of the internal deterioration factors.
Materials with good initial ageing
properties i.e. with few internal deterioration factors
may last longer in a bad environment than an object with
bad ageing properties i.e. with many internal deterioration
factors kept in a good preservation environment.
Good storage conditions will counteract
deterioration of materials with bad ageing properties to a certain
point, while bad storage conditions will always accelerate deterioration
processes.
Recommended Measures for Improving
Preservation Conditions
The best way to preserve photographic
materials is to emphasise measures on preventive care. The necessity
of proper storage materials envelopes, boxes, archive furbishing
etc. and storage climate cannot be over estimated.
If possible a photographic collection
should be divided and stored in two archives; an active and a
passive. The active archive is for frequently used material
mainly copies of originals and the passive archive is for
long term keeping of the originals. The passive archive should
have a stable climate with low temperature and relative humidity.
A number of recommendations exist but they do not differ significantly
from the requirements listed in the following table. These are
weighted for a good cost/effectiveness ratio. The requirements
can be difficult to achieve but must always remain the target.
The target temperature and humidity readings can be relaxed provided
that the conditions are kept stable and with the proviso that
the humidity level is kept above 25% and below about 65% - the
level above which moulds are encouraged to grow. The penalty in
most cases is, however, a shorter life expectancy for the carriers.
STILL IMAGES | ||||||
Negatives |
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b/w Prints |
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Cellulose Nitrate Film |
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Colour Negatives |
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Colour Slides |
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Colour Prints |
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MOVING IMAGES | ||||||
Colour Films |
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b/w Safety Films |
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b/w Nitrate Films |
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b/w MICROFILM | ||||||
Silver-gelatine |
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Basements and attics are usually not
suitable for storing photographic materials. Basements are usually
very humid and often accommodate plumbing which, if it starts
to leak, may cause irreversible damages. Attics, if not properly
insulated, will have an uncontrolled climate affected by the outdoor
conditions.
High temperature and high relative humidity
(RH) accelerates most deterioration processes. The cooler the
temperature the slower the deterioration rate. The control of
relative humidity is even more important in an archive with photographic
materials.
These types of damage may occur when
the RH is TOO HIGH:
The following damages may occur when
RH is TOO LOW:
It may be difficult to keep the air in
an archive clean since most major archives usually are situated
in the centre of major cities. But it is nevertheless of the utmost
importance to keep the areas free from air pollutants as possible.
They are very reactive with substances in both b/ w and colour
photographs. Listed in the following table are the requirements
for clean air in photographic collections.
Other harmful substances exist in the
air but good chemical filters customised for the substances listed
in the table will control these as well.
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If the collection includes any
nitrate moving films, seek advice from the local fire authorities
about the storage requirements, the maximum quantity of film that
can be kept in one storage area and any other restrictions that
they may require. This action is not merely good advice - it is
essential. Nitrate movie film is considered to be an explosive
by the fire authorities in many countries.
Conclusion
Photographic objects belong to a very
delicate category of our cultural heritage which need special
attention by trained personnel. Materials are susceptible to air
pollutants, both fuel generated and emitted from furbishing and
protective materials in repositories, as well as high humidity
and temperature. It is important, therefore, to be in control
of the preservation environment. It is also important to be able
to identify the photographic methods represented in a collection
and thus be aware of specific preservation problems.
Specifications, methods and measures
for improving the preservation environment for photographic materials
can be found in special literature and standards. Some of these
are listed below.
Standards
ISO 417 | Photography Determination of residual thiosulfate and other related chemicals in processed photographic materials Methods using iodineamylose, methylene blue and silver sulfide. |
ISO 543 | Cinematography Motion picture safety film Definition, testing and marking |
ISO 3897 | Photography Processed photographic plates Storage practices. |
ISO 4331 | Photography Processed photographic blackandwhite film for archival records Silvergelatin type on cellulose ester base Specifications |
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ISO 4332 | Photography Processed photographic blackandwhite film for archival records Silvergelatin type on poly(ethylene terephthalate) base Specifications |
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ISO 5466 | Photography Processed safety photographic films Storage practices |
ISO 6051 | Photography Processed reflection prints - Storage practices. |
ISO 6200 | Micrographics - First generation silver-gelatine microforms of source documents - Density specifications |
ISO 8126 | Micrographics - Diazo and vesicular films - Visual density - Specifications |
ISO 9718 | Photography Processed versicular photographic film Specifications for density |
ISO 10214 | Photography Processed photo graphic materials Filing enclosure for storage. |
ISO 10602 | Photography Processed silvergelatine type blackandwhite film Specifications for stability. |
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ISO 51 | Photography Density measurements Part 1: Terms, symbols and notations |
ISO 52 | Photography Density measurements Part 2: Geometric conditions for transmission density |
ISO 53 | Photography Density measurements Part 3: Special conditions |
ISO 54 | Photography Density measurements Part 4: Geometric conditions for reflection density |
Reference Literature
Garry Thomson
The Museum Environment
ButterworthHeinemann, Oxford 1986
ISBN 07506 2041 2
Preservation of Microfilming does it have a future?
Proceedings of the First National Conference of the National Preservation Office, at the State Library of South Australia, 46 May 1994, Canberra 1995
ISBN 0 642 10639 8
Guidelines for Preservation Microfilming in Canadian Libraries
National Library of Canada for The Canadian
Cooperative Preservation Project (In English and French) ISBN
0 660 57970 7
Henry Wilhelm & Carol Brower
The Permanence and Care of Colour Photographs: Traditional and Digital Colour Prints, Colour Negatives, Slides, and Motion Pictures.
Grinnell, Iowa, 1993, ISBN 0911515003 (hardcover)
ISBN 0 911515 01 1 (paperback)
Imaging Processes and Materials
Ed. by John M. Sturge, Vivian Walworth & Allan Shepp, New York 1989
ISBN 0 442 28042 6
James M. Reilly
Care and Identification of 19thCentury Photographic Prints
KODAK Publication No. C25, CAT 160 7787
ISBN 0 87985 365A
Schrock, Nancy Carlson
Preservation and storage
In Picture Librarianship ed. By Helen
P Harrison, Library Association, London 1985
The Conservation of Photographs
Eastman Kodak, Rochester, New York,
1985
Brown, Harold Godard
Basic Film Handling
FIAF Preservation Commission, Brussels
Brown, Harold Godard
Problems of Storing Film for Archive Purposes
British Kinematography No. 20, 1952
The Book of Film Care. Publication F-30
Eastman Kodak Ltd, Rochester, New York,
1983
Handling, Preservation and Storage of Nitrate Film
FIAF, Brussels, 1987
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