A photosensitive composition used in forming patterns for colour picture tubes comprises (a) a copolymer of acrylamide and diacetoneacrylamide and (b) a water soluble aromatic bisazide compound. This composition is improved by incorporating a sulfonated vinyl monomer such as sodium-p-styrene-sulfonate in the copolymer. This composition has the advantage that it follows a reciprocal failure law; i.e. the degree of cross linkage of B is related to the intensity i and exposure time t of irradiation by the equation B =f(i.t.P) where p is Schwarzschild's constant, which is in the range 0