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Conservation of Photographic Materials

By Susie Clark, Peter Winsor and Stephen Ball

Photographs have been with us since the 1830s, and cinematography is more than a century old. Photographic materials are such mundane and commonplace objects that we sometimes tend to regard them as disposable ephemera or treat them as if they were virtually indestructible, bringing a high risk that we will lose the important cultural and historical information they convey.

Photographic Materials

Every photograph or film is a package of three elements: a base, an image-forming material, and some kind of medium to hold the image on to the base. The light-sensitive image materials and the medium together form the emulsion. Each of these elements - base, image, medium - has its own care and conservation requirements.

Bases

The most common bases are glass, plastic and paper, though metal, wood and fabric are used in some obsolete or special processes. Paper is the commonest base for prints, whereas reversal (positive) slides and cine film use plastic bases.

In some early processes like the daguerreotype the exposed plate also provided the finished picture. Later processes adopted the now familiar negative-positive approach, in which the exposed plate or film becomes a negative that can be used to produce any number of positive prints.
The development of cellulose nitrate in the late 1880s liberated photography from its dependence on the rigid glass negative and also made cine film possible. Unfortunately, higher RH and temperature conditions cause nitrate film to break down into harmful and strongly acidic products that fade silver images, soften gelatine emulsions, corrode metal enclosures and damage other items in the vicinity. Nitrate breakdown products are also dangerously oxidising, and have been responsible for many devastating fires in the past.

Some nitrate film is identified by the word 'Nitrate' along one edge, though the absence of this label is no guarantee of safety film. Any film or negative with 'safety' or 'safety film' along the edge is not on a nitrate base. Another good guide is age: for example, 16mm or 8mm film was never manufactured on a nitrate base, and after 1951 all 35mm film was manufactured on acetate or polyester.

Most films and negatives in museum or small private collections are on an acetate (triacetate, or cellulose acetate) base. Although acetate is safe, like nitrate it degrades under conditions of acidity, warmth and moisture. This degradation is known as the 'vinegar syndrome' after the distinctive smell of acetic acid migrating to the film surface. The acid eventually softens the gelatine emulsion, and may increase the fading of colour dyes. In time the film base becomes brittle and shrinks away from the largely unchanged gelatine emulsion, and the resultant 'channelling' appears as a network of small channels over the film.

Since the 1980s, polyester has been used for most film, microfilm and fiche. The material is strong as well as physically and chemically stable, which means that the life of polyester film is likely to be determined by the durability of the emulsion layer rather than the base. A polyester film looks semi-transparent when viewed from the side against a light, whereas an acetate film appears dense and black, and when sandwiched between crossed linear polarisers produces colour fringes.

Emulsions

Photographic emulsions include albumen, collodion (for wet plate systems) and gelatine. The emulsion layer carries the image materials - silver compounds for black and white and dyes for colour - and in colour stock may also be layered with filters.

The sensitised emulsion is exposed to light in the camera and subsequently processed. Photographic processing first reveals the image (development), and then renders it 'permanent' (fixing). Each process uses its own cocktails of chemicals in a particular sequence, and there are many variations in development and fixing methods and formulations.

The important thing for the collector and museum is that each process has different characteristics and requires different handling and treatments. Unless you are expert yourself, seek advice on identification from a specialist conservator.

Cine Film

Cine films share many aspects of care and conservation with other photographic materials - a film, like a photograph, consists of an originally photosensitive image layer supported by a base.

Cinematography places great demands on the film base material, which must be transparent, strong and flexible. Film is almost universally transported by sprockets (toothed wheels or rollers) or claws that engage in holes in the film base. The larger gauges such as standard 35mm carry holes along both edges; 16mm may carry one or two sets of sprocket holes, depending on whether there is a soundtrack, and the smaller amateur gauges have a single line of holes.

For each film in your collection, you must identify the base material and also the processes used before you can create the right conditions for care and conservation. Unless you are an expert yourself you will need expert help, especially with less common gauges. If the film is a commercial or other 'professional' product, it is almost certainly a print, whereas an amateur film is more likely to be made up from the original film that was exposed in the camera and subsequently processed.

Both amateur and professional films will bear the scars of their projection history - sprocket hole damage, scratches, colour fading and other problems. Commercial films may come in standard reel lengths (typically up to 2000 ft); by contrast, amateur gauges are typically in shorter lengths from 50 ft to about 400 ft. There will probably be splices in various states of repair.

Solvent-cement splicing was the standard joining method for both nitrate and acetate film types. Splicing bonds two pieces of film together by applying a solvent to film ends clamped in a special splicing machine. Although splicing was formerly an everyday activity for editors, projectionists and amateur film-makers, you should regard it as an aspect of remedial conservation. In other words, leave it to the experts.

The Viewing Problem

Whether a film is historically important on an international scale or just the ephemeral and personal record of an unknown amateur, its value remains hidden until it is projected. Unfortunately, projection is a source of wear, tear and damage. Films wear out even when run on well-maintained projectors in professional hands.

Projection creates two main sources of danger: light and attendant heat, and mechanical wear and damage from the film transport. Common problems from these sources include torn sprocket holes, broken splices, burnt frames, running scratches, and a build up of dirt and dust over time. During its normal projection life a film probably succumbed to mechanical wear and damage before it showed marked signs of fading, which is more likely to result from chemical changes in storage.

Never be tempted to show an original film on a projector from the same period in the name of authenticity. Projectors are beyond the scope of this fact sheet, and should be treated as separate working objects whose operation must be managed in line with a carefully defined policy.

Film itself is a form of working object. Accordingly, each 'working' copy of a film, whether on conventional film stock or videotape, should be accompanied by an operating log that is updated whenever it is viewed (or perhaps on a daily or weekly basis in the case of a videotape that is shown continuously as part of an interactive display). Whatever your policy on viewing, there is one overriding principle: always run a copy of the film, never the original.

A Safe Environment

As for all museum objects, create a stable environment for photographic materials. Aim for an RH of between 20 and 50%, with the 20-30% range best for gelatine emulsions. This should be combined with cool temperatures of not more than 2ºC where possible (but see 'Storage and Display' below).

Excess moisture promotes chemical change in the emulsion layer and encourages mould; too little moisture causes emulsions, paper and plastics to crack and become brittle. High temperatures also promote chemical change, and are particularly bad for colour film manufactured before about 1980.

Some pollutants can affect photographic materials, mainly by promoting chemical changes in the emulsion layer. The biggest dangers are unsuitable materials coming into contact with the film; building or decorative works, treatment or cleaning materials and solvents nearby; dust and dirt; ozone from older types of laser printers and photocopiers; and food, clothing and smoking.

Light

Light is both the source and the worst enemy of photographic images. None of the materials used to create photographic images is truly permanent, so continued exposure to light will result in the image losing contrast, colour, stability, and ultimately information content. Yet for the public, a photographic collection only has value when it is viewed. Conventional paper photographs require reflected light; and slides, filmstrips, fiche and motion pictures require transmitted light.

Do not overlook simple solutions. There are many ways to control the light falling on an object. Photographs only need to be illuminated when visitors are looking at them, so consider curtains, blinds and screens for windows, visitor-operated time switches for electric lights, and curtains for display cabinets. Never leave a photograph in full sunlight. And wherever possible, show copies of photographs and films rather than the originals (see below).

Try to reduce both the duration and the intensity of light falling on photographs. Ultraviolet (UV) light is especially damaging and must be filtered out. The special UV filters and varnishes applied to windows and lamps need regular checks because they become ineffective within a few years.

Storage and Display

You may safely cold store most roll and cut film negatives, paper prints and transparencies, and all types of cine film. The exceptions are tintypes and collodion wet plate negatives and positives, and other collodion and albumen photographic materials; these could be harmed by low temperatures, so avoid storing them below 5ºC.
Keep items in tightly sealed bags and containers to protect them from the high humidity in some freezers and refrigerators. When taking photographs out of cold storage for research or display, allow them to acclimatise at room temperature for about three hours before taking them out of the bags, to stop condensation forming.

Glass negatives and slides are obviously vulnerable to mechanical damage. Protect the image layer and plate surface by wrapping the glass in suitable paper, then store the wrapped plates in padded boxes or museum board boxes. Add a board separator or a purpose-made metal divider at every fifth plate. Large plates
(10×8 inches or bigger) are better stored horizontally, separated by museum board dividers at no more than four per box. Lantern slides may be kept in their original wooden box provided the box is in good condition and not freshly varnished or polished.

Nitrate, acetate and polyester negatives from roll films usually occur as singles or, in the case of 35mm roll film negatives, short strips of 4-6 frames. Cut film, which supplanted glass plates for most comparable purposes, produces single negatives in a variety of sizes. Keep each strip or negative in its own envelope to prevent abrasion and deterioration in one negative spreading to others. Unstable materials should never be stored near stable ones, and nitrate stock creates special problems of its own (see below).

Always store negatives and prints singly in museum-quality paper or plastic - ideally polyester - sleeves. (Never use PVC anywhere in the store.) These allow the contents to be viewed without direct contact, and can be boxed or suspended in a stove enamelled or powder finished filing cabinet.

Unbacked prints may have curled over time as the image layer and the paper base expanded and contracted at different rates. Never force a photograph flat, which could cause the image layer to crack or even flake off. Store the sleeved prints like negatives in cabinets, and never in large piles.

Many old photographs were firmly mounted on board or card. If the mounting is clean and stable, and the photograph has survived in this form for many decades, there is no reason to remove it. Only strip off the backing if it is harming the photograph - use a scalpel, and ideally call in a conservator. The same applies to an album containing photographic prints, which is a museum object in its own right. Store albums flat, preferably singly in boxes or chests, or wrap them in washed unbleached calico if they have no fragile external decoration. Avoid stacking or book-style shelving that could damage decoration, hinges, clasps and keys.

Some photographs, such as daguerreotypes and collodion positives, are protected by a close fitting case or frame with a hinged cover. The case is an integral part of the object. Store daguerreotypes and other cased photographs horizontally in boxes or cabinet drawers.

Cine Film and Materials

If you have many films and can justify the cost of special-purpose shelving, use metal racking or shelves and store the film cans flat. Avoid large piles of cans, and beware of overloading the shelf system. If you improvise film storage in an area used for other objects, do remember the low-temperature storage requirements of film, especially colour stock.

Good film storage must be backed up by good documentation and housekeeping. Film cans must be clearly and fully labelled, and also reel-numbered if they contain parts of multi-reel films. Be sure to keep originals and copies separately, and to identify them as such on cans and film leaders.

Film copies for viewing must be properly rewound - the right way round - and checked for breaks and other faults immediately after projection. Old-fashioned hand rewinding machines - used gently - give operators a chance to check the film as it is wound back. Keep films wound emulsion side inwards on plastic reels, and store them in archive quality polypropylene or clean metal cans. Store paper wrappings or card liners separately.

Nitrate: A Special Case

Cellulose nitrate film and negative stock pose special storage hazards; only specialist archives should consider keeping them. If you can justify the high costs of nitrate film storage in the light of your museum's acquisitions policy, you must build a separate store that is approved by the local fire authorities. Do not store even small quantities of nitrate stock in the same area as other types of film: decomposing nitrate film affects other material.

Check your insurance: many policies specifically exclude risks associated with cellulose nitrate film.

Handling Photographic Materials

Do not touch photographic materials, especially on their image-bearing surfaces. Always wear cotton gloves. The sweat and natural oils from human skin can initiate or accelerate chemical changes and attract dust and dirt, or directly degrade an image such as a daguerreotype by creating a blemish.

Use only copies of photographs for display and access: most visitors and researchers are probably interested in a photograph's content, and are satisfied with a good print. Transparent sleeves and envelopes help to reduce the risk of handling because the item can be viewed while it is still safely inside.

Work in a clean space, and always use two hands to hold a photograph. Remove envelopes from photographs - never the other way around - and gently slide the item on to a stiff board if it is fragile. Ask a conservator to separate prints or negatives that appear to be stuck together.

Copying

In nearly every case, it is the content of a photograph or film that is of interest to visitors, not the specific instance or materials. This means that a copy is the natural choice for display.

Copying is not without its wider problems. For example, you should always check copyright issues before making a copy. There is also a choice of available processes for both photographs and motion pictures. Whatever the medium, however, the aim of copying is to reproduce the original as accurately as possible in all salient respects without damaging or changing the original.

Photographs and other flat originals can be photocopied, scanned (and thus digitised for computer storage and manipulation) or re-photographed. Important considerations here are minimal light exposure during copying, and adequate support for the original - never use document feeders on photocopiers, for example, and always ensure any glass or other contact surface is scrupulously clean. Remember that curved originals must not be forced flat, so there may have to be a compromise on image quality or accuracy.

Film copying options are broadly similar, with copy prints, video and digitisation the choices: film no longer has to be copied to film. Video may be the best option for those with limited resources: a new print is expensive, and digitisation demands substantial computing storage resources. You may face difficult choices if you have many films in your care: which should you copy? You may not want to keep uncopied (and unseen) films in archival storage indefinitely; one option may be to offer or loan them to another institution.

Take as much care of your copies as you do your originals. The more rapidly a copy wears, the sooner you must return to the original. It makes sense to borrow the approach of film studios and distributors: when copying, make at least one new master rather than a succession of ad hoc copies. Then, when the copies wear out, you can return to the new masters for the replacements. If the original film or photographic print is worth keeping, it remains untouched in safe cold storage.

Sources of information and advice

For more information about caring for photographs see:

Ball, S. et al, The care of photographic materials and related media, MGC, London, 1996.

The North-East Document Conservation Centre website contains a number of useful factsheets.

http://www.nedcc.org/

For more information about private conservation work please contact:

Conservation Register
Tel: 020 7721 8246

Conservation Register (Scotland)
Tel: 0131 668 8668

Copies of this fact sheet can be provided in alternative formats. Please contact Viola Lewis, Information Officer at MLA for further information.

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