Security labels which are difficult to counterfeit

A system for tagging articles. A glass is fabricated from (1) a combination of oxides and (2) one or more rare earth elements. The glass is divided into particles or fragments, which are attached to the article. When the particles are excited by specific radiation, they emit a characteristic signature, in terms of a collection of frequencies, each frequency having a characteristic amplitude and decay time. However, the particles cannot be counterfeited, or reverse-engineered, because, at present, no systematic data is available which correlates a particle's characteristic signature with the composition and processing of the particle itself. Thus, at best, a trial-and-error approach must be taken in attempts at counterfeiting, which is considered impossible.