TABLE VI. Shrinkage of EK Nitrate MP Film. 



fiCZ, YEARS 

 Fig. 3. Shrinkage vs. age for triacetate and nitrate prints scrapped afte- 

 normal theater use. Measurements made at 70 F and 50% R.H. 



|Q4 



!„_ o a 



Fig. 4. Average rate of shrinkage of processed triacetate 

 39aim motion-picture positive film at 90 F and 90% R.H. Con- 

 trolled tests on strips freely exposed to circulating air; all meas- 

 urements made after reconditioning at 70 F and 50% R.H. 



Kodak aerial films are now coated on two bases. Kodak Aerographic 

 films, (Type lA) are made on low shrink topographic base, suitable for use 

 in accurate mapping work. Regular Safety Aero base is used for Kodak 

 Ektachrome Aero film, and Recon film. The latter has somewhat higher 

 shrinkage characteristics than the Type lA. A comparison of dimensional 

 changes in the two bases is shown in Table VII. 



Since 1941, Type lA (topographic) film base has been made from 

 cellulose acetate butyrate. Between 1938 and 1941, it was made from cellu- 

 lose acetate propiomate. Both these bases have substantially lower humid- 

 ity expansion coefficients than cellulose acetate, used prior to 1938. 



264 



