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ScreenSound Australia

Screensound Australia is constantly undertaking research in areas relating to cellulose acetate materials. Below are descriptions of four such projects they are currently working on. For more information, please contact Mick Newnham, email Mick.Newnham@screensound.gov.au.

Motion Picture Film Collection Risk Assessment Survey

The most common method of preserving film is by controlling both temperature and relative humidity. It is high cost operation requiring expensive to run and maintain plant. At best, this slows down the decomposition. However, without benchmarks it becomes theoretical as to how successful the established conditions are at controlling the rate of decomposition.

The National Collection maintained by ScreenSound Australia holds over 300 000 reels of film. Assessment of each object is clearly impossible due to time and resourcing implications. A statistical approach was needed, as was a non-destructive and repeatable method of assessment for the selected objects.

A project was established to provide a bench mark from which the effectiveness of the current storage conditions could be measured. The project tested a statistically useful number of objects in specific populations of our collection for a pass/fail result in relation to Vinegar Syndrome by using IPI AD Test Strips. Then by using statistical analysis the test results were extrapolated to the whole collection.

Once a benchmark had been determined an ongoing program of repeatable testing over time to monitor the rate of change in these populations was established. This provided management information regarding the relative risks and rate of change of these risks.

Ventilated film cans, their effect on the diffusion of the decomposition by-products from motion picture film.

One of the major issues in film preservation is the decomposition of the cellulose ester polymers used as the film base. In short acid by-products formed during decomposition tend to catalyse and accelerate the reaction. Apart from using controlled low temperature and relative humidity storage to slow the reaction, passively removing the acid by-products from the decomposing film is another approach. In particular encouraging diffusion of the acids away from the film base is considered an effective control method.

Film cans are comparatively well sealed and provide a buffering effect for the internal microclimate. This sealing also reduces the ability of the decomposition acids to diffuse from the film. Punching holes in the sides of film cans to allow ventilation of the diffused gases is often practiced. ScreenSound undertook research to determine how effective this strategy is for the long-term storage of motion picture film.

Results showed that the "leading edge" of the can slows the airflow and increases the pressure and the "trailing edge", with higher airspeed, creates a proportionally lower pressure area. The air flows through the can to equalise this pressure differential. The simple arrangement of two holes aligned in the airflow proved to be the most efficient location for creating the desired airflow through a film can and thus aid in diffusion.

Danweb testing

In investigating the airflow through a ventilated film can it was observed that in order to maximise airflow around the film, and thus diffusion, space was required underneath the film pack. DanCan International, in consultation with ScreenSound, undertook a project to design a structure that would both raise the pack and improve airflow. The result of this project is the "Danweb". ScreenSound is currently undertaking research to determine wether this approach is effective in reducing the acid content within the film.

Investigation into the mechanism of reducing the free acid level inside decomposing motion picture films using a low tension "preservation" wind.

Acid by-products are known to accelerate the decomposition of cellulose acetate films. One of the methods believed to aid in the removal, or increased diffusion, of these acids from the film is that of a low tension or "preservation" wind.

It is commonly believed that such a wind allows for an increased airflow and thus diffusion of acid by-products from the film. Previous research has shown that airflow, even in a ventilated can, is minimal. An almost saturated steady state concentration of acetic acid within the film can may be reached, impairing the ability of the acetic acid to diffuse from the film.

Other research suggests that gelatin acts as a buffer to the acids escaping from the deteriorating base. The stabilisation of the base then can be influenced by the degree to which the gelatin can absorb these acids. It is hypothesised that as shrinkage of the film occurs over time even the current preservation wind standards still place a great deal of pressure on the gelatin which is believed to restrict the emulsion's ability to absorb the acid as it is formed.

ScreenSound is investigating whether it is the restrictions in the uptake of acetic acid by the emulsion due to pressure on the emulsion or the ability of the film pack to more readily diffuse acidic decomposition by-products in more loosely wound films that has the greatest impact in lowering the rate of decomposition.

Last updated 17 June 2002


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