Optically Variable Ink
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Optically variable ink (OVI) is an anti-counterfeiting measure used in modern currency, used on many major banknotes.
The ink displays two distinct colors depending on the angle the bill is viewed at. The United States fifty-dollar bill, for example, uses color shifting ink for the numeral 50 so that it displays copper at one angle, and bright green in another.[1]
OVI is particularly useful as an anti-counterfeiting measure as it is not widely available; the major manufacturer is a Swiss company called SICPA.
Optically variable inks (OVI) - Color-shifting inks reflect various wavelengths in white light differently, depending on the angle of incidence to the surface. An unaided eye will observe this effect as a change of color change while the viewing angle is changed. A color copier or scanner can copy a document only at one fixed angle relative to the card’s surface.[1]
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