Tuesday, September 8, 2009

Maintaining Audiovisual Record (Part 1)

By Khairul Izzuan bin Ahmad

Storage Condition

Poor storage condition for audiovisual records impede their preservation. High relative humidity (for an example, above 60 percent) encourages the growth of mold and other fungi on film based materials, whose binders are derived from organic compounds. High relative humidity also causes oxidation of silver content in film and metal compounds in audio and video tape. In addition, it causes deterioration of the oxide coating on magnetic tapes, leading to clogged magnetic tape heads and scratched tapes. Warm temperatures tend to accelerate undesirable chemical and physical changes in audiovisual records (including x-ray photographs), such as shrinkage of film base and emulsion, and fading of colour film images.

In recent years, preservation have become increasingly concerned about the longevity of a major class of safety film composed of cellulose-acetate. Several scientific studies have independently shown how adverse storage condition create a form of hydrolysis in acetate-based film that develops free and the emission of acetic gas, leading to the total degradation of the film.Identified as the "Vinegar Syndrome", this destructive chemical process potentially affects all forms of acetate film.

Polyester-based film, widely used for sheet film since the 1970s, is much less prone to self-destructive tendencies because the base resist chemical and physical changes, although the emulsion is still vulnerable to damage from excessive heat, humidity, and harmful gases.Nonetheless, when there is a choice such as in motion picture stocks, polyester is preferable to cellulose triacetate because of its superior long-term stability.

The fading of colour film images is also of great concern. colour dyes, made of organic materials, are not permanent. Heat, humidity and exposure to light accelerate colour dye fading, resulting in the discoloured images that may be found in many older collections. Cold storage below freezing combined with low relative humidity effectively retards colour fading.

Pollutant gases in urban or suburaban environments are potetntially harmful as are off-gases from newly painted rooms, new furniture or flooring, and chemical storages areas.Agencies should store aidiovisual records in areas not subject to gases and fumes.

Providing proper storage conditions for audiovisuals materials is a materials is a complex problem, one that probably cannot be fully solved in the facilities available to most agencies. Nevertheless, audiovisual records (including x-ray photographs) should not be stored where the temparature exceeds 72 degrees Fahreinheit and the realtive humidity is higher than 50 percents. Even cooler and drier storage conditions are desirable to increase the life expentency of audiovisual records. The storage environment should be cool and dry and relatively free from harmful gases.


Adopted The National Archives

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