Abstract: A method of forming a film of photonic crystal material. A first process is performed upon a material capable of having a photonic crystal structure, this process causing deformation of the material so as to form a film in which incident light received by the material is selectively reflected or transmitted to generate a first optical effect in the film. A second process is performed upon substantially all of the film which applies a shear stress to the film. This causes a change in the material structure so as to generate a second optical effect in the film, different from the first optical effect, in response to incident light. Security films, devices, articles and documents formed using the method are also discussed.

Abstract: A method is provided of detecting a region of raised material on a document surface. A surface of the document is illuminated with at least one angled radiation beam such that any raised material on the document surface reflects the radiation. The surface containing the raised material is imaged using at least one radiation detector. The image is then processed to detect the existence on the document surface of the raised material. The illuminating step causes a reflection and/or shadow to be generated from at least one edge of the raised material. The processing step detects the location of the material using the said reflection and/or shadow from the at least one edge.