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Oct.. 1944
PROPERTIES AND BEHAVIOR OF FILM
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during development and shrink back again during drying. Most films also undergo a small permanent shrinkage during processing. However, if the film is not brought to equilibrium with air at the same relative humidity after development as it was before, the permanent processing shrinkage may be completely masked by the temporary expansion or contraction due to change in relative humidity. This frequently happens in the case of motion picture film, which at the time of perforating may have a moisture content equivalent to that at equilibrium with air between 50 per cent and
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TIME WEEKS
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FIG. 16. The effect of relative humidity on the rate of shrinkage of processed Eastman Nitrate Motion Picture Positive film in the lengthwise direction at 70 F. (Film in strips having free access to air.)
60 per cent RH. If the film is removed from the drying cabinet after processing with a moisture content equivalent to that at equilibrium with air between 70 per cent and 80 per cent RH, the permanent shrinkage of the raw stock plus the processing shrinkage will be masked by the humidity expansion, so that the pitch of the film may even be slightly longer than the standard.
The Effect of Storage Conditions on the Shrinkage of Film.— After development, photographic film continues to shrink at a decreasing rate throughout the remainder of its life. The degree of permanent shrinkage which occurs depends on the type of film and the treatment it receives. The effect of several extrinsic variables