A method of forming an optically variable security device is provided. In the method, a photonic crystal material is provided and a process is performed upon the material which causes deformation of the material so as to form a first region (A) for which incident light received by the crystal material is selectively reflected or transmitted to generate a first optically variable effect, and a second region (B) for which incident light received generates an optical effect, different from the first optically variable effect. Corresponding devices having first and second regions are also disclosed.