Opal's iridescence inspires anti-counterfeit cash

0 Comments | AFP, July, 2007

PARIS (AFP) — The next generation of banknotes may incorporate an iridescent shimmer inspired by the opal that changes colour when you turn or twist the note, New Scientist reports in next Saturday's issue.

The iridescence comes from polyester film with photonic crystals, whose layered structure blocks certain wavelengths of light at some viewing angles, but lets other wavelengths through.

Until now, iridescence in plastic sheets comes through etching patterns into the film, but the result is often poor, with dull colours and a "milky" effect if viewed from the wrong angle.

The new film, devised by the University of Southampton in Britain, the German Institute for Polymers in Darmstadt and the pharmaceutical giant Merck, "shimmers from every angle" and...