A method of forming an array of microimage elements that vary in their material composition, the method comprising: applying a first region of a layer of a first material to a surface of a first material carrier (101a, 102a); applying a second region of a layer of a second material, different from the first material, to a surface of a second material carrier (101a, 102a); blending together the first and second regions of the layers of first and second material (1, 2) such that a blended region of the layers of first and second material exhibits a gradual change in relative concentration of the first and second materials along a first direction, the step of blending together the first and second regions of the layers of first and second material comprising bringing a first blending surface (101b, 102b) into contact with the first material on the surface of the first material carrier and moving the first blending surface (101b, 102b) relative to the surface of the first material carrier (101a, 102a) along a direction corresponding to the first direction to spread the layer of first material along the direction corresponding to the first direction, and bringing a second blending surface (101b, 102b) into contact with the second material on the second material carrier (101a, 102a) and moving the second blending surface relative to the surface of the second material carrier along a direction corresponding to the first direction to spread the layer of second material along the direction corresponding to the first direction; bringing the blended layers of first and second material in the blended region into contact with a patterned material carrier (111, 112), the surface of the patterned material carrier defining a pattern corresponding to the array of microimage elements, the patterned material carrier selectively removing the first and second material (1, 2) in at least the blended region in accordance with the pattern; and transferring the blended layers of first and second material (1, 2) defining the array of microimage elements on to a support layer. applying a first region of a layer of a first material to a surface of a first material carrier (101a, 102a); applying a second region of a layer of a second material, different from the first material, to a surface of a second material carrier (101a, 102a); blending together the first and second regions of the layers of first and second material (1, 2) such that a blended region of the layers of first and second material exhibits a gradual change in relative concentration of the first and second materials along a first direction, the step of blending together the first and second regions of the layers of first and second material comprising bringing a first blending surface (101b, 102b) into contact with the first material on the surface of the first material carrier and moving the first blending surface (101b, 102b) relative to the surface of the first material carrier (101a, 102a) along a direction corresponding to the first direction to spread the layer of first material along the direction corresponding to the first direction, and bringing a second blending surface (101b, 102b) into contact with the second material on the second material carrier (101a, 102a) and moving the second blending surface relative to the surface of the second material carrier along a direction corresponding to the first direction to spread the layer of second material along the direction corresponding to the first direction; bringing the blended layers of first and second material in the blended region into contact with a patterned material carrier (111, 112), the surface of the patterned material carrier defining a pattern corresponding to the array of microimage elements, the patterned material carrier selectively removing the first and second material (1, 2) in at least the blended region in accordance with the pattern; and transferring the blended layers of first and second material (1, 2) defining the array of microimage elements on to a support layer.