Patent ID: 8610893

Claim:
A process for detecting a marking on an article, comprising: a. marking the article, by contacting the article with at least one marker, wherein an absorption spectrum of the at least one marker has at least one narrow band with a half-height width of <1500 cm −1 and the at least one narrow band is in at least one wavelength region of an electromagnetic spectrum selected from the group consisting of UV, visible, and IR, b. irradiating the article with electromagnetic radiation comprising a wavelength range which at least partly overlaps with the at least one narrow band of the at least one marker, c. optionally, during step b., effecting a change in a position of the at least one narrow band by a solvatochromic, electrochromic, photochromic or thermochromic effect, d. determining wavelength absorption by the article in a range comprising the wavelength range which at least partly overlaps with the at least one narrow band of the at least one marker, and e. detecting a marking on said article from said wavelength absorption, wherein the irradiation of the article with electromagnetic radiation is performed using at least two narrow-band radiation sources, switching back and forth between a wavelength at which the marker absorbs and a wavelength at which there is no absorption.