"The supports can be sub-coated with known subbing materials such as: copolymers and terpolymers of vinylidene chloride; and acrylic monomers, such as acrylonitrile and methyl acrylate; unsaturated dicarboxylic acids, such as itaconic or acrylic acid; carboxymethyl cellulose; polyacrylamide, and similar polymeric materials." . . . . . . .