Film conservation treatments are integral to preserving the longevity of film materials.

These treatments can be categorised into several processes that address the physical, chemical and aesthetic degradation of films over time.

Cleaning, repairing, and safeguarding film materials requires a thorough understanding of the materials' characteristics and degradation patterns to ensure that conservation efforts are both practical and minimally invasive.

Cleaning film

Over time, films accumulate dust, dirt, and grease on both the emulsion and the base due to handling and exposure to environmental factors such as static electricity.

Not only does dirt diminish the projected image quality, but it also can cause physical damage through abrasion and attract chemicals that accelerate deterioration.

The most common form of cleaning film involves the use of perchloroethylene, a chlorinated solvent. This solvent is employed in combination with ultrasonic agitation and buffer rollers that remove dirt and grease without damaging the film. The ultrasonic waves cause cavitation, producing microscopic bubbles that implode and dislodge contaminants.

Safety

All cleaning activities must be conducted with proper ventilation and the use of protective equipment to ensure the safety of both the conservator and the film.

Organic solvents

Historically, 1,1,1 trichloroethane ('Genklene') was a popular solvent until it was banned due to environmental concerns related to ozone depletion (Montreal Protocol, 1989).

Its replacement, perchloroethylene, is less efficient and poses higher health risks, particularly in vapour containment. Other alternatives, such as isopropyl alcohol and ethanol, are commonly used for specific cleaning tasks but come with their own set of risks, including dissolving plasticisers from the film base or adversely affecting the dyes used in the image-forming process.

Hydrofluoroethers (HFEs) have emerged as a safer alternative with low ozone-depletion potential; however, they remain costly and require specialised cleaning machines capable of efficiently capturing the vapours.

Naphtha, a petroleum fraction, is also employed due to its efficiency in grease removal, although it is highly flammable and requires specialised equipment.

Water-based cleaning

Water and mild surfactants are occasionally used in cleaning, although they present challenges for archival films, especially those with cellulose ester bases, such as acetate.

Water can penetrate the gelatin emulsion of a film quickly, potentially exacerbating the degradation of the base material. Drying films after aqueous cleaning becomes critical, as any residual moisture left in the film can contribute to further chemical breakdown.

Drying marks (also known as shell marks) are often a by-product of water-based cleaning methods, resulting in blemishes visible on projections or copies.

Lacquers and other post-processing coatings

Lacquers and protective coatings have been applied to films over the years to prevent abrasion during handling and projection. Some early colour negatives, particularly in laboratories, were lacquered to protect against scratches.

However, cleaning these coated films with organic solvents can be problematic, as some coatings may dissolve or become cloudy when exposed to certain chemicals.

Beeswax was commonly used as a protective coating on film edges to help projectors handle freshly processed film more effectively. This wax was applied to the outer edges of the film, and over time, it could spread into the image area, potentially impacting preservation.

Spot cleaning

Spot cleaning involves treating specific areas of dirt, grease, or residue using a cotton swab moistened with an appropriate solvent.

This method is most effective when applied delicately from the outer edges of the spot toward the centre, preventing the spread of contaminants.

Dry dust back

For light dirt removal, the dry dust back technique is a simple method that uses a clean cloth (usually made of cotton or polyester) to remove loose particles from the film surface gently. The cloth must be free of dirt and contaminants to prevent scratches.

This method is most suitable for surface dust and requires great care to avoid damage to the film.

Wet dust back

The wet dust back technique involves using a dampened cloth to remove dirt.

This method requires careful management of solvent use and is typically carried out with machines that provide consistent solvent application, such as the ECO Film Cleaner. These systems use felt pads to deliver solvents to the film surface.

Particle transfer rollers

Particle transfer rollers (PTR) cleaners employ slightly sticky urethane-coated rollers that attract dust particles as the film passes through. PTRs are effective for light surface dust but have limited success in removing grease or dirt stuck by adhesive residues. These systems require regular cleaning to prevent damage to the film, especially when working with flaking emulsions.

Ultrasonic film cleaners

Ultrasonic cleaning utilises high-frequency sound waves (typically at 20 KHz) to create cavitation bubbles in a solvent, which effectively loosen dirt and grease.

The film is transported through a tank of heated solvent, and the cavitation phenomenon dislodges contaminants without damaging the film.

However, ultrasonic cleaning machines require frequent maintenance to ensure they function correctly, and poorly maintained machines can lead to film scratches. It is also important to manage the tension applied to films during cleaning to prevent damage.

Buffer roller film cleaners

Buffer roller cleaners are used for removing deeply embedded dirt or sticky oils. The buffer process utilises soft rollers and a continuous flow of solvent to clean the film gently.

This method is more effective than ultrasonic cleaning for older films with stubborn grime but requires ongoing maintenance and testing to ensure the rollers remain clean and free of dirt that might be transferred onto the film.

Case study: cleaning mould off film

Caution: Mould and mould spores are potentially hazardous to human health. It is crucial to implement adequate health and safety precautions before attempting to clean any mouldy film. Always wear proper protective gear, including gloves, masks, and goggles, and work in a well-ventilated area to minimise exposure.

Step 1: Work on one film at a time

If multiple films are included in the work order, handle only one film at a time, leaving the other films in their enclosures to prevent cross-contamination. This ensures that mould spores do not spread between films.

Step 2: Check film packaging

Inspect the film's packaging for signs of mould. If the box is integral to the film's provenance or valuable as part of the collection, retain it for further conservation work. Otherwise, please dispose of the box by sealing it in a plastic bag to prevent the spread of spores.

[Example: 16 mm cardboard film box]

Step 3: Use a HEPA filter vacuum

Using a HEPA filter vacuum cleaner (High-Efficiency Particulate Arrestor), lightly vacuum all surfaces of the film and reel, including any loose film around the film pack. This step will remove much of the loose mould, dirt, and rust particles that could cause further scratching of the film during handling.

Note: HEPA filters capture 99.97% of airborne particles as small as 0.3 microns. Mould spores typically range from 2-8 microns in diameter (Meyer et al., 2021).

Step 4: Secure loose film

Wind any loose film onto the film pack and secure the loose end with splicing tape. Ensure that the tape is only applied to the base of the film to prevent potential damage to the emulsion.

Step 5: Removing and cleaning the flange

Carefully remove the reel flange by prising the locking tabs using a thin, flat-blade screwdriver. Be gentle to avoid damaging the delicate metal tabs. Only work the screwdriver away from your hands and body to prevent injury in case of slippage.

Once the flange is removed, use the HEPA filter vacuum to clean both the film pack and the inside of the flange.

Step 6: Cleaning the film and flange with Isopropanol (IPA)

After removing as much mould and debris as possible, use a cotton bud lightly moistened with isopropyl alcohol (IPA) to wipe the film's surface gently. Repeat this process on the flange. IPA helps remove residual mould spores and contaminants from the film.

Step 7: Reassemble the film

After cleaning, replace the flange and ensure the locking tabs are re-secured without excessive pressure to avoid bending or creasing the metal. If necessary, use a flat-blade tool to flatten the tabs carefully.

Step 8: Rehousing the film

If the original packaging is in good condition (i.e., not mouldy or contaminated), rehouse the film in its original enclosure. Clean the work area and any equipment used with methylated spirits to ensure no residual mould or contaminants remain.

Repairing film

Film repair is essential to ensure films can be safely handled, transported, and projected through film-handling equipment, such as printers, scanners, or projectors. All repairs should meet the following criteria:

• Durability: Repairs should be long-lasting and stable over time.
• Thickness: The repair should not be too thick, maintaining the film's focus when it passes through the film gate.
• Shrinkage: The repair should account for any shrinkage along the length of the film, as the film tends to shrink over time.
• Clean Edges: The repair should be neatly trimmed, with no overhanging pieces that could catch on the equipment.

Perforation maintenance: Repairs must maintain the correct number of perforations per frame (e.g., four perforations per frame for 35mm film).

Splices

A splice is used to join two sections of film in such a way that the join is invisible when projected. Traditionally, film splices are made using film cement. Ideally, cement is used for all film repairs, as it provides a more stable, long-term solution compared to adhesive film splicing tape.

• Cement splices v tape splices: When done correctly, film cement repairs have fewer long-term issues than splicing tape. Over time, film splicing tape may dry out, lose its adhesive strength, or form a sticky residue that attracts dirt, ultimately leading to deterioration. Polyester-based films should be spliced with tape or ultrasonic welders as film cement cannot be used effectively on them.
• Ultrasonic splicing: Ultrasonic splicing is a process used for polyester films. The ultrasonic splicer uses high-frequency sound waves to generate heat that melts and fuses the polyester. This method is not typically recommended for cellulose acetate films, as heat can cause additive migration and create voids in the polymer, thereby weakening the splice.
• Splice testing: The durability of a splice should be tested for tensile strength (resistance to separation under force) and peel strength (resistance to separation under twisting). A minimum of 2.5 kg for tensile strength and 500g for peel strength is typically required.

Repairing a damaged splice

When repairing a broken splice, the first step is to gently separate the two sections of film and remove any dried cement that may be present. If shrinkage is significant, the splice can be made manually by carefully aligning the film and applying cement.

• Butt splice: For splicing two pieces of film where there is insufficient area in the frame to create a standard splice, a butt splice can be used. This involves aligning the perforations of both pieces and reinforcing the joint with an "I" shaped scrap of film.
• Hand-built splice: In cases where frames are missing or too damaged, a hand-built splice may be necessary. This process involves carefully trimming the damaged section, scraping the emulsion, and aligning the perforations before applying film cement.

Special considerations for 16 mm A and B rolls

For 16 mm films, the frame lines are fragile, making it difficult to make robust splices without intruding into the image area.

The A and B roll system is used in 16 mm editing, where splices occur in black spacer areas between scenes. When repairing such films, it is critical to preserve the integrity of the spacer and maintain proper synchronisation between the image and sound elements.