Abstract: A security document including a substrate of transparent polymeric material, and opacifying layers provided on opposing sides of the substrate, the opacifying layers acting to guide light propagating within the substrate, wherein the substrate is formed with at least one micro-prism for diverting light propagating within or entering the substrate.

Abstract: A security device (2) including a substantially transparent material (6) having a first side and a second side. An array of lenses (4) is arranged on the first side of the material (6) and an ablative layer (8), which is reflective or at least partially opaque, is arranged on the second side of the material. The ablative layer has one or more patterns (12, 16) formed by removal of the ablative layer, for example by laser radiation (10, 14). The or each pattern (12, 16) is viewable at a particular viewing angle (?, ?) or range of angles through the array of lenses. Also disclosed is a method of manufacturing a security device.

Abstract: A security document or token such as a banknote (40) is provided which has a transparent portion (42) of plastics material which includes a security device (50). The region (44) surrounding the transparent portion (42) and preferably all the remaining part of the banknote (40) is printed with indicia. The security device (50) includes regions (52, 54, 56 and 58) of embossed lines extending at different angles to each other defining different shapes that are visible to a greater or lesser extent upon transmission and reflection of light as the note is tilted, rotated or viewed from different angles relative to a light source. The embossed lines in some of the regions (52 and 54) are finer than coarser and deeper and more widely spaced lines in the other regions (56 and 58). The coarser, deeper lines are of such a thickness and width to be detected by touch in addition to being visible by the naked eye.

Abstract: A diffraction grating of reflective or transmissive lines is formed by a regular matrix of pixels each containing a respective curvilinear portion of one or more of said lines. When the pixels are illuminated, each generates a two-dimensional optical catastrophe image diffraction pattern whereby the total image diffraction pattern of the grating is optically variable but structurally stable. The invention further provides a diffraction grating of reflective or transmissive lines, comprising a multiplicity of diffraction grating regions which are at least partly separated by multiplicity of grating free regions. Each grating free region has a dimension which is at least large enough to be resolved by the human eye, the total grating free areas not exceeding about 20 to 50% of the total area of the grating. The disclosed diffraction grating is useful as a security device for currency or credit cards.