A method of making a security device, comprising: (a) forming an array of focussing elements on at least a first region of a focussing element support layer, by: (a)(i) applying a first transparent curable material either to the focussing element support layer or to a casting tool carrying a surface relief corresponding to the focussing elements, over an first sub-region of the first region and applying a second transparent curable material to a second sub-region of the first region laterally offset from the first sub-region, the first and second transparent curable materials having different optical detection characteristics from one another; (a)(ii) forming the first and second transparent curable materials (205a,b) with the casting tool; and (a)(iii) curing the first and second transparent curable materials (205a,b) in the first region, so as to retain the surface relief characterised in that the first and second transparent curable materials (205a,b) are applied to the focussing element support layer or to the casting tool only over the area corresponding to that of the respective sub-regions (202a,b) and the casting tool carries the surface relief over an area extending beyond that of the first region. (a) forming an array of focussing elements on at least a first region of a focussing element support layer, by: (a)(i) applying a first transparent curable material either to the focussing element support layer or to a casting tool carrying a surface relief corresponding to the focussing elements, over an first sub-region of the first region and applying a second transparent curable material to a second sub-region of the first region laterally offset from the first sub-region, the first and second transparent curable materials having different optical detection characteristics from one another; (a)(ii) forming the first and second transparent curable materials (205a,b) with the casting tool; and (a)(iii) curing the first and second transparent curable materials (205a,b) in the first region, so as to retain the surface relief characterised in that the first and second transparent curable materials (205a,b) are applied to the focussing element support layer or to the casting tool only over the area corresponding to that of the respective sub-regions (202a,b) and the casting tool carries the surface relief over an area extending beyond that of the first region. (a)(i) applying a first transparent curable material either to the focussing element support layer or to a casting tool carrying a surface relief corresponding to the focussing elements, over an first sub-region of the first region and applying a second transparent curable material to a second sub-region of the first region laterally offset from the first sub-region, the first and second transparent curable materials having different optical detection characteristics from one another; (a)(ii) forming the first and second transparent curable materials (205a,b) with the casting tool; and (a)(iii) curing the first and second transparent curable materials (205a,b) in the first region, so as to retain the surface relief characterised in that the first and second transparent curable materials (205a,b) are applied to the focussing element support layer or to the casting tool only over the area corresponding to that of the respective sub-regions (202a,b) and the casting tool carries the surface relief over an area extending beyond that of the first region.