IR Metameric Inks
Inks which have similar spectral features in visible light (perceived as having the same color) but different under IR illumination (some inks absorb IR light, others reflect). When examining an image printed using IR metameric inks, only a part of the image is visible in IR light. This security feature is based on the ability of document materials and inks to absorb or reflect IR light.
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b
Fig. 1. Brunei. Passport issued in 2008:
a — back endpaper. Paper substrate. White light; b — the same. Text fragments which absorb IR light look dark. The background image is transparent in IR light. IR light
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b
Fig. 2. Macau. Passport issued in 2009:
a — page 48. Paper substrate. White light; b — the same. Fragments of the image and text are different in the degree of IR light absorption. So, they look semitransparent or dark on the light background. IR light