Optically Variable Ink (OVITM) chosen for its unique colour shifting properties is applied to the currencies of more than 50 countries. An significant colour difference at viewing angles of 90 degrees and 30 degrees respectively makes colour copying impossible. New manufacturing techniques for the interference pigment (OVP) provide ever better cost/performance ratios. Screen printing presses newly available on the market guarantee production speeds of 8000 sheets/hour or 130 meters/minute in the case of web printing, perfectly in line with the traditional equipment for manufacturing of currency. Specifically developed ink formulations allow UV-curing at high speed or oxidative drying to create highly mechanically and chemically resistant colour shifting prints. The unique colour shifting characteristics together with overprinting in intaglio give design opportunities providing the best protection against colour copying or commercial reprint. Specific designs of OVP together with high security ingredients allow the formulation of machine readable optically variable inks useful for the authentication and sorting of documents.
Anton F. Bleikolm,
"New design opportunities with OVI", Proc. SPIE 3314, Optical Security and Counterfeit Deterrence Techniques II, (1 April 1998); doi: 10.1117/12.304689; https://doi.org/10.1117/12.304689