Abstract: A security document or token such as a banknote is provided which has a transparent portion of plastics material which includes a security device. The region surrounding the transparent portion and preferably all the remaining part of the banknote is printed with indicia. The security device includes regions 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 the light source. The embossed lines in some of the regions are finer than coarser and deeper and more widely spaced lines in the other regions. The coarser, deeper lines are of such a thickness and width as to be detectable 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.