A method of producing a patterned birefringent product, having at least steps (I) to (III) in this order: (I) providing a birefringent pattern builder having an optically anisotropic layer containing a polymer having unreacted reactive groups; (II) heating a region of the birefringent pattern builder; and (III) subjecting the birefringent pattern builder to a process that reacts at least a part of the unreacted reactive groups in the optically anisotropic layer.