Abstract: The invention relates to a security document 10 and a method of making the security document 10. The security document 10 has an optically transmissive region with a first surface and a second surface on an opposite side to the first surface. On a portion of the first surface is a first opacifying layer 14, with an area B of the optically transmissive region not being covered by the first opacifying layer 14. Similarly, on a portion of the second surface is a second opacifying layer 16, with an area A of the optically transmissive region not being covered by the second opacifying layer 16. The uncovered area B of the first surface does not substantially overlap the uncovered area A of the second surface. Further, the uncovered area B of the first surface and uncovered area A of the second surface appear to be substantially contiguous when viewed in transmitted light.

Abstract: A moiré magnification device for authenticating security articles, the moiré magnification device comprising: an array of micro focusing elements; and an array of micro images; wherein the array of micro focusing elements and the array of micro images are correspondingly aperiodic such that the micro focusing elements generate moiré magnifications of the micro image when viewing the device at predetermined viewing angles. A device such as this raises the complexity and difficulty of the task facing would-be counterfeiters. The use of an aperiodic micro focusing element array and micro image array is not immediately apparent, as the moiré magnifications observed by the viewer appear the same as that of a regular device with periodic arrays. In this way, the aperiodic aspect of the design remains covert until the moiré device is more closely and deliberately analysed.

Abstract: An optical security device is disclosed which includes a diffraction layer having a plurality of diffraction elements and a high refractive index layer, wherein the high refractive index layer is applied on the diffraction layer such that selected regions of the diffraction layer have the corresponding diffraction elements partially uncovered by the high refractive index layer and other regions are substantially covered by the high refractive index layer. Accordingly, the optical security device has a first security feature associated with the diffraction layer and a second security feature associated with the high refractive index layer. An image is viewable from the regions of the high refractive index layer, either, covertly by placed an index matched item over the device or, overtly, through selection of the thickness of the high refractive index layer.

Abstract: An optical device including: a first surface; and an arrangement of pixels on the first surface, wherein a plurality of the pixels includes a zero-order diffraction element, such that each zero-order diffraction element is configured for providing a zero-order diffractive effect.

Abstract: An optical device for authenticating articles of value, the optical device including: a first diffractive structure for generating a first diffractive image; a second diffractive structure for generating a second diffractive image; and a non-diffractive structure; wherein, the first and second diffractive structures, and the non-diffractive structure, are positioned relative to each other such that when viewed from a first angle, both the first and second diffractive images are visible, and when viewed from a second angle, the first diffractive image is visible while the second diffractive image is not visible.

Abstract: A security element, security device and method of forming a security device wherein the security element includes focusing elements, a first group of image elements, and a second group of image elements, each image element being located in an object plane to be viewable through a focusing element, and being located a distance from the focusing element such that the focal point width of the focusing element in the object plane is substantially equal to the size of the image element or differs from the size of the image element by a predetermined amount.