Embossed optically variable devices

A security device (3) and a method of forming a security device (3) is provided in which a sheet (1) has a substantially transparent or translucent layer (10) and a reflective layer (11) with at least part of the reflective layer (11) being visible through the transparent or translucent layer (10) from a first side of the sheet (1). The sheet (1) is blind embossed from the first side through the transparent or translucent layer (10) and onto the reflective layer (11) to form a transitory embossed image (3). The transitory embossed image (3) may be provided in a window or half-window (2) formed by applying one or more opacifying layers (14) to the substrate (10) except in the area containing the reflective layer (11) and transitory embossed image (3) on one or both sides of the substrate (10). In one embodiment, the reflective layer is a highly reflective metallic ink (11). In another embodiment (not shown), the reflective layer is an optically variable pigment which provides a colour shift between two distinct colours with the colour shift dependent upon viewing angle. In further embodiments, the transitory embossed image comprises macro-embossings with micro-embossings formed on the sides of the macro-embossings. Each of the embodiments of transitory embossed images produces unusual visual switching effects which cannot be reproduced by photocopying and which are difficult to counterfeit.