ARTICLE TO BE CERTIFIED OF TABULAR MATERIAL AS OBJECT OF FORGERY AND ARTICLE CONTAINING CERTIFYING DEVICE JOINED TO SAID ARTICLE

摘要

An improved authenticating device comprises a substrate bonded to the sheet material, the substrate having a reflective diffractive structure formed as a relief pattern on a viewable surface thereof, and a transparent material 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.