Importance

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Abstract

A hard to simulate, readily distinguishable from counterfeits, optical interference authenticating device comprises a substrate, and two optical interference coatings in interfacial contact on one side of the substrate, one of the optical interference coatings being a contrast coating, the other of the optical interference coatings being a form depicting coating for depicting a form relative to the contrast coating. The optical interference coatings each comprising at least one optical interference layer the material and thickness of which has been selected for the coatings to have different, particular, known spectral reflectance and spectral transmittance characteristics from one another when viewed at a particular angle, such that the form depicting coating is visible by reflected or transmitted light of particular coloration, when viewed at the particular angle, at least in part by optical interference of light partically reflected or transmitted at the interfacial contact. A further optical interference contrast coating may be provided on the substrate and the form depicting coating may be sandwiched between the contrast coatings. The substrate may be transparent, semi-transparent or opaque, depending how the spectral characteristics are to be observed. A marginal edge portion of the form depicting coating may taper in thickness to provide a multicolored auriole around the form. A plurality form depicting coatings may be provided which overlie one another to provide a more complex pattern.

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First Claim