Currency producers are facing dual marketplace demands to increase bank note circulation life and to employ increasingly effective security features against counterfeiting. Diffractive optically variable devices such as foil patches, stripes and windowed thread have become popular security features used for bank notes throughout the world, but historically have suffered in their ability to match the durability of the bank note substrate itself. A study to find a durable, diffractive OVD led to the development of a windowed-thread feature designed to pass stringent durability criteria for laundry, chemical soak and other performance tests. Diffractive-film production methods, demetallization techniques, thread construction and applied coatings were key factors in achieving this durability.
William J. Bartz, William J. Bartz,
"Durability of optically variable devices on bank notes", Proc. SPIE 4677, Optical Security and Counterfeit Deterrence Techniques IV, (19 April 2002); doi: 10.1117/12.462737; https://doi.org/10.1117/12.462737