Security device and authenticatable item

A security device for mounting to an authenticatable item, the security device carrying a number of symbols identifiable to the naked eye, there being at least two sets of at least three symbols, wherein all the symbols within a set are substantially identical, are positioned in a non-overlapping, regular geometric arrangement, and at at least one common viewing angle of inclination, exhibit substantially the same optical performance, the optical performance varying with inclination viewing angle.

A method of manufacturing a security device carrying a number of symbols identifiable to the naked eye, there being at least two sets of three symbols, wherein all the symbols within a set are substantially identical, are positioned in a non-overlapping, regular geometric arrangement, and at at least one common viewing angle of inclination, exhibit substantially the same optical performance, the optical performance varying with inclination viewing angle, the method comprising providing on a substrate a number of symbols identifiable to the naked eye, there being at least two sets of at least three symbols, wherein all the symbols within a set are substantially identical, are positioned in a non-overlapping regular geometric arrangement, and at at least one common viewing angle of inclination, exhibit substantially the same optical performance, the optical performance varying with inclination viewing angle.

A shim for use in manufacturing a diffractive security device, the shim having a surface relief pattern which can be impressed into a substrate and is constructed so as to impress a corresponding surface relief pattern in the substrate and define said diffractive security device which carries a number of symbols identifiable to a naked eye, there being at least two sets of at least three symbols, wherein all the symbols within a set are substantially identical, are positioned in a non-overlapping, regular geometric arrangement, and at at least one common viewing angle of inclination, exhibit substantially the same optical performance, the optical performance varying with inclination viewing angle.