Conservation treatments for motion picture films are complex processes that require a thorough evaluation of the film's condition and stability before any advanced treatment can be performed.

This is critical to ensure that the treatment will not cause further damage, especially when dealing with older films or films suffering from deterioration.

For films with unstable emulsions or bases, particularly those exhibiting significant physical or chemical degradation, advanced conservation treatments should be undertaken with great caution.

When considering treatments such as aqueous solutions, it is essential to assess the possible risks involved to avoid irreversible damage to the film.

Common problems with film deterioration

Two of the most common film deterioration issues, particularly for films stored under high relative humidity, are ferrotyping and blocking. Both occur as a result of moisture absorption and improper storage conditions for the film.

Ferrotyping

This happens when films are tightly wound, and the gelatin layer absorbs moisture, causing it to swell. The softened gelatin layer then presses against the adjacent layer in the film reel, leading to a glossy, shiny surface known as ferrotyping.

This surface alteration can degrade the visual quality of the film and affect light transmission during projection.

Blocking

Blocking occurs when the emulsion layers of the film adhere to one another, often due to high humidity and tightly wound film.

This results in the film being 'stuck' or blocked, making it difficult to unwind without damaging the emulsion. Blocked films are particularly susceptible to physical damage during unwinding, and if the adhesion is too strong, it could even tear the film.

Risk of advanced conservation treatments

Most advanced treatments require the use of aqueous solutions or solvents, which can pose risks to deteriorating films. The older the film, the more susceptible it is to damage during treatment.

The treatment of film should always begin with a stability test on an inconspicuous area of the film. This test must allow for some time equal to or longer than the proposed treatment duration to ensure that no adverse reactions occur.

Some risks to be mindful of during these treatments include:

• Extreme shrinkage: Poor handling, particularly during rewetting or rewashing, can cause films to shrink dramatically, potentially resulting in irreversible damage to the emulsion and base.
• Gelatin disintegration: Many films, especially those with older emulsions, are prone to gelatin disintegration when exposed to aqueous solutions.
• Base weakening: Moisture absorption can weaken the film base, resulting in brittleness and an increased risk of physical damage.

In some cases, the emulsion may dissolve completely, or the film base may shrink dramatically, making it unusable.

Therefore, extreme caution must be exercised during these processes to prevent further damage to the film.

Detailed considerations before treatment

Before treatment, consider the following:

Documentation

Before any treatment, accurate and comprehensive documentation is essential. This should include an initial condition report, noting the film's physical and chemical state.

Proper documentation ensures that all changes during the treatment process are accurately recorded, which helps assess the treatment's success and allows for future evaluation of the film's long-term stability.

For example, a case study from the National Film and Sound Archive (NFSA) in the 1990s demonstrated that ethanol swabbing for mould removal resulted in localised shrinkage along the edges of some films.

Further analysis led to the discontinuation of ethanol swabbing in favour of using isopropyl alcohol, which did not interact with the triphenyl phosphate (TPP) additives in the film base (McCormick-Goodhart, 2019).

Tracking conservation treatments

Tracking systems are essential when working on multiple films, especially when they are treated in batches. Traditionally, minilabs used 'twin checks'—pairs of adhesive labels with matching numbers for each film. These labels ensured that films could be tracked through each stage of processing.

A similar system should be used in conservation treatments to ensure films are correctly identified throughout all stages. This system is particularly crucial when different technicians handle films or undergo various stages of treatment. It ensures the proper matching of films to their original reels, sound components, or other production elements.

Rewashing to reduce surface blemishes

Rewashing is the process of running a film through a washing cycle to remove water-soluble dirt and stains and to reduce the appearance of minor scratches.

During rewashing, the gelatin emulsion swells, which can help diminish the appearance of surface damage, although deeper scratches will remain visible.

This technique is beneficial for cleaning films that have collected surface dirt over time, particularly from handling or storage conditions.

What can be treated?

Rewashing is effective for films that have accumulated soluble dirt and mild surface scratches. However, it is important to note that rewashing will not remove oils, fingerprints, or grease from the film surface.

The effectiveness of rewashing depends on the severity of the damage to the emulsion. Light scratches may become nearly unnoticeable, while deeper damage will still be visible.

Risks and considerations

Rewashing poses several risks, such as:

• Weakening of the film base: Moisture absorption during rewashing can weaken the film base, particularly for older films or those that are already brittle.
• Damage to perforations and splices: Splices and perforations may become fragile or damaged during the rewashing process.
• Decomposition and image dye solubility: Rewashing may cause decomposition of the film, particularly when there is a significant build-up of acid in the base, which can increase the solubility of the emulsion and image dyes.

Rewash solution

A typical rewash solution consists of:

• Sodium polymetaphosphate: 500g/100L
• Sodium sulphite: 840g/100L
• Sodium metabisulphite: 1,000g/100L.

The chemicals should be dissolved in a small amount of warm water and then diluted to the working strength.

Cautions

The rewash solution and film processing machine must be monitored carefully. If the temperature in the rewash tanks changes too drastically, the emulsion could undergo reticulation, where it swells and folds, resulting in a distorted image.

Older emulsions are more prone to this damage due to the loss of stabilising properties over time (Hunter & Chapman, 2021).

Reducing ferrotyping

Films subjected to high humidity and tightly wound for extended periods may exhibit ferrotyping, where the gelatin surface takes on a glossy appearance due to pressure from adjacent film layers. This glossy surface is undesirable, as it affects the film's light transmission and will be visible during projection.

What can be treated?

Ferrotyping can be reduced in films that have been tightly wound and have developed a shiny appearance due to pressure from adjacent layers. However, the film must not be significantly blocked, as excessive adhesion between layers could complicate the treatment.

Treatment method

To reduce ferrotyping, a soft nap paint roller can be introduced into the film path during the rewash process. This roller helps to roughen the emulsion surface and restore the film's original matte finish, improving its light transmission qualities.

Unblocking wet-blocked film

Wet-blocked films occur when the emulsion layers become adhered to each other, often due to high humidity and tight wind tension. When this occurs, the film becomes very difficult to unwind without damaging the emulsion.

Unblocking treatments work by reducing the adhesion between the layers, allowing the film to be safely unwound.

What can be treated?

Films that are wet-blocked due to high humidity or tight wind tension can benefit from unblocking treatments. Films exposed to high heat, such as those damaged by fire, may also be treated using this method. However, films that have severely decomposed may not respond well to this treatment, and extra caution is needed before applying it to decomposed films.

Unblocking solution

A typical unblocking solution includes sodium polymetaphosphate (15g/L).

This solution should be replaced daily to prevent bacterial contamination, which can lead to further damage to the gelatin emulsion.

Redimensioning or de-shrinking shrunken film

Cellulose acetate films may experience shrinkage over time due to the loss of residual manufacturing solvents and additives. Shrinkage can lead to issues with perforation pitch and overall film distortion, making it difficult for the film to be transported through equipment that relies on sprockets.

Treatment options

• Water vapour treatment: The film is placed in a sealed chamber above a dish of distilled water for 24 hours. This treatment aims to soften the emulsion, making the film more flexible and reducing shrinkage.
• Acetone-glycerol-water solution: A mixture of acetone, glycerol, and water can be used as an alternative to water vapour. This solution is particularly effective for more resilient films.
• Camphor treatment: Camphor, often dissolved in olive oil, can be used to increase film pliability by releasing vapours that soften the emulsion.

Risks

The primary risk with redimensioning treatments is the potential for mould growth, especially when the film is exposed to moisture for extended periods. Additionally, some films may become opaque, resulting in a loss of transparency and making duplication impossible.

Conclusion

Advanced conservation treatments are crucial for maintaining the integrity of motion picture films. These treatments are often necessary to preserve the film's physical and chemical properties, especially in the face of environmental degradation, such as high humidity or chemical decomposition.

While these treatments can be highly effective, they must be carried out with extreme caution, ensuring that each step of the process is thoroughly tested and documented.

The goal is to ensure the preservation of the film's image quality while minimising the risk of further damage.