A Barometer for Film Health
Motion picture film is a physical object made of a plastic base (historically cellulose nitrate or acetate, now polyester) coated with a light-sensitive emulsion. Over many decades, the chemical components in the film base slowly break down, causing the film strip to lose moisture and plasticizers. This process results in the film physically shrinking from its original dimensions. A shrinkage gauge is the tool used to precisely measure this decay.
Function and Application
The device itself is simple but highly accurate. It consists of a small plate with two pins. One pin is fixed, and the other is connected to a sensitive dial indicator. The film’s sprocket holes (perforations) are carefully placed over these pins. The gauge is calibrated so that a fresh, healthy piece of film of a specific length reads as 0% shrinkage. If the film being measured has shrunk, the perforations will be closer together, and the dial will indicate the exact percentage of shrinkage.
Measuring shrinkage is one of the very first and most critical steps an archivist takes when assessing a film element. The reading from the gauge provides vital information:
- Handling and Safety: Severely shrunken film is brittle and its perforations will no longer align with the sprockets on standard film equipment. Attempting to run shrunken film on a conventional projector, printer, or scanner can cause the perforations to tear, catastrophically damaging the film. The shrinkage measurement tells the archivist which specialized equipment is safe to use.
- Condition Diagnosis: The degree of shrinkage is a direct indicator of the film’s chemical stability. For acetate film, a high shrinkage percentage is a key symptom of ‘vinegar syndrome,’ an irreversible form of chemical decay. This alerts the archivist that the film needs to be prioritized for digitization before it deteriorates further.
In essence, the shrinkage gauge acts as a thermometer for a film’s health, providing the essential data needed to plan a safe and effective strategy for its long-term preservation.