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4. Photographic Materials

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.

Preservation Climate Requirements for Photographic Materials


Temp

±/24h

±/Year

RH

±/24h

±/Year

STILL IMAGES







Negatives

<18°C

±1°C

±2°C

30%-40%

±5%

±10%

b/w Prints

<18°C

±1°C

±2°C

30%­40%

±5%

±10%

Cellulose Nitrate Film

<11°C

±1°C

±2°C

30%­40%

±5%

±10%

Colour Negatives

<2°C

±1°C

±2°C

30%­40%

±5%

±10%

Colour Slides

<2°C

±1°C

±2°C

30%­40%

±5%

±10%

Colour Prints

<2°C

±1°C

±2°C

30%­40%

±5%

±10%

MOVING IMAGES







Colour Films

-5°C

±1°C

±2°C

30%

±2%

±5%

b/w Safety Films

<16°C

±1°C

±2°C

35%

±2%

±5%

b/w Nitrate Films

4°C

±1°C

±2°C

50%

±2%

±5%

b/w MICROFILM







Silver-gelatine

<18°C

±1°C

±2°C

30%­40%

±5%

±10%

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.

Air Quality Requirements in Archives for Photographic Materials

Gas

Active Archive

Passive Archive

SO2

1 g/m3

1 g/m3

NOx

5 g/m3

1 g/m3

O3

25 g/m3

2 g/m3

CO2

4 5 g/m3

4 5 g/m3

Fine Particles

75 g/m3

75 g/m3

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

ISO 4332

Photography ­ Processed photographic black­and­white film for archival records ­ Silver­gelatin type on poly(ethylene terephthalate) base ­Specifications

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.

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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