preheated electric oven for approximately 10 minutes at 120 u00b0 125 u00b0 c the release promoting ability of the surfactant containing film is evaluated using the procedure described hereinafter under the subheading 34 determination of release and readhesion values 34 a surfactant whose aqueous test solution yields a dry film that demonstrates a release value less than that obtained from unmodified polyvinyl alcohol film is a migratable release promoting agent for purposes of the release coating compositions of this invention release layers were prepared from a 10 aqueous solution of the appropriate polyvinyl alcohol to which was added 5 based on weight of polyvinyl alcohol of a release promoting agent zinc ammonium carbonate boric acid and sodium chloride were added where indicated in the following examples as 0 5 m solutions all solutions were adjusted to ph 10 with concentrated aqueous ammonia wet films were cast on clean 4 u00d7 6 inch 10 2 u00d7 15 2 cm glass plates using a 0 004 inch 0 1 mm bird bar and the films were dried immediately in a 255 u00b0 f 125 u00b0 c forced draft oven for 10 minutes heating up of the 1 16 inch 1 6 mm thick plates required a significant portion of the time the coated plates were evaluated within 12 to 24 hours of preparation according to the following procedure a 5 inch 12 7 cm region at the end of a 12 u00d7 1 inch 30 5 u00d7 2 54 cm strip of highland masking tape 3m company was gently placed in.