Abstract: The invention provides a plurality of substantially same planar pigment flakes, each formed of one or more thin film layers. Each flake has a face surface and a flake border delimiting the face surface; the flake border undulates in the plane of the flake. The flakes have a pre-selected shape, may have a symbol or a grating thereon. A method of manufacturing of these flakes including the steps of: (a) providing a substrate having a plurality of one-flake regions and a plurality of depressions or protrusions disposed therebetween and not extending into the one-flake regions, (b) coating the substrate with a releasable coating, and (c) removing the releasable coating and breaking it into the flakes; wherein two adjacent of the one-flake regions are separated by at least three of the depressions or protrusions for facilitating the breaking of the releasable coating into the flakes.

Abstract: A tubular main frame (2) for an aeroplane, bridge, or pressure vessel, for example, comprises a honeycomb structure with cells (4) thereof distributed round the periphery of the frame and along the frame, the cells each being at least pentagonal, preferably largely hexagonal.

Abstract: A holographic technique for the detection of position of known items so as to be able to reject those samples which do not lie within certain defined spatial parameters. A plate which contains a single exposure of the three dimensional holographic image of an object is illuminated by parallel reference beams from a laser to allow the reconstruction of a real focused image of the object. A displacement translator supports the object and permits displacement thereof in three directions all at right angles to one another. The coincidence of the object and its holographic image are detected either optically by means of a stereoscopic microscope, or electrically by means of a stereoscopic microscope and a photo-diode.