Almost all conventional acid filter dyes can be rendered nondiffusing in emulsion or thin auxiliary layers, without lowering their phys.-mech. properties or interference with their bleachability or washing-out during processing by a small amt. of a mordant (I; R1,R2 = C1-4 alkyl; n = 300-600; and X- = anion). Added as storable 5-10% soln. they have a low water absorption and have little effect on the viscosity of gelatin coatings. Thus, 2 solns. were made both contg. gelatin 100 and a pentamethine dye 8, and as mordant soln. A an imide of maleic anhydride interpolymers of US 3,048,487 (CA 59; 7726b) 4 g, and soln. B I (R1,R2 = Me, n = 300, X = Cl-) 4.15 g. A Yielded a 2.3m filter layer having an optical d. of 1.09, and B one of 2.0m and 0.98, resp. The water absorption of the layers was 4.1 and 3.0 g H2O/m2, and the dye diffusion after 2 wet contacts with a layer of unhardened gelatin 43 and 2% (as optical d.), resp. [on SciFinder (R)]