The third cause of permanent dimensional change is release of 

 strain, or recovery from deformation. If film base is stretched daring 

 manufacture under conditions which do not permit reorientation of the 

 molecules, deformation, or creep, occurs, resulting in lengthwise 

 extension and widthwise contraction. Rapid cooling retards recovery 

 of the deformation (primary creep) due to "freezing in of strain". This 

 strain may be released at some time during the life of the film, with con- 

 sequent lengthwise shrinkage, and widthwise expansion. Where such a 

 strain exists, the rate of recovery is increased by both heat and moisture. 



Table TV shows the effect of temperature on the rate of shrinkage 

 of an earlier film base, EK16 mm safety reversal. Shrinkage was mea- 

 sured in the lengthwise direction, on processed film strips exposed freely 

 to air at the indicated temperatures, and 20 percent relative humidity. 



TABLE IV 



262 



