Preserving Older Microfilm and Combating Vinegar Syndrome

Many corporate and government archives hold microfilm from the 1930s to the mid-1990s produced on cellulose acetate base. Storage at uncontrolled temperature and humidity exposes this film to a chemical reaction known as vinegar syndrome. This guide covers prevention, remediation and migration to current technology.

Highlights

• Polyester base films replaced acetate from the late 1970s and, when properly processed and stored, last at least 500 years
• Heat, humidity and acid are the main factors that turn acetate into acetic acid
• Once acidity passes 0.5 the reaction accelerates, and above 2.0 the film shrinks and warps
• A-D Strips and Molecular Sieves are tools for monitoring and prevention
• The best solution for damaged film is duplication onto polyester base film

Film structure and the acetate problem

Each film is made of several layers: the light-sensitive gelatin emulsion, anti-scratch, anti-static and antihalation layers, and the base, which is the thickest layer (2.5 to 7 mil). In acetate, acetyl groups split off in the presence of moisture, heat and acid and produce acetic acid. The film base loses its dimensional stability, becomes brittle, and the images are damaged. Even temporarily taking film out of storage into a warm, humid office environment speeds up deterioration.

Assessment steps

• Identify the base type: Films made after 1995 are usually polyester. Acetate tears easily, while polyester is almost impossible to tear. Polyester also conducts light through its edges (light piping).
• Odor: A vinegar smell indicates damaged film; isolate it and contact a service provider to determine the level of deterioration.
• Monitoring: Film without odor should be monitored with A-D Strips placed in the box.
• Prevention: Molecular Sieves absorb moisture and acetic acid but are not a substitute for proper storage conditions.
• Conversion: With high acidity or shrinkage, the only option is duplication onto polyester film, which also allows multiple copies, a change of polarity or digital scanning.

Criteria for choosing a duplication lab

• Provides duplication samples from damaged film, maintains test target levels between generations and produces film free of lines
• Produces consistent contrast and density from image to image and roll to roll
• Documents quality control procedures, inspection and acceptance criteria
• Active membership in the EPM INFOGUARD Quality Monitoring program
• Performs the Methylene Blue test on every shift
• Offers polysulfide toning for oxidation resistance and Molecular Sieves for humidity control
• Provides process traceability (audit trail) if tests fail
• Additional services: expert consulting, film scanning and OCR

Protection against oxidation

Microfilm, both acetate and polyester, is vulnerable to pollutants that oxidize the emulsion silver and create tiny spots on the image. Polysulfide toning converts the developed silver to silver sulfide, which is more resistant to moisture and oxidation.