Authenticated item with diffractive-substractive authenticating device

摘要

Sheet material items (100) subject to counterfeiting e.g. bank notes or credit cards have an integral or bonded authenticating device which comprises a substrate (200) having a reflective diffractive structure (206) formed as a relief pattern on a viewable surface thereof, and a transparent material (208) covering the structure. Specified grating parameters of the diffractive structure, obtainable at low cost, result in peculiar, but easily discernable, optical color properties that cannot be copied by color copying machines. ……