RE: Plasticized dope mixture
Modern dope does not need the plasticizers; they already have them. There was a small revolution, chemically, when Dacron was first used in the 50's to cover real airplanes over cotton; they had to change the formulas to make it more pliable. The EPA made them change it again in the 90s, so now it is even softer than it use to be as a byproduct.