Metameric Ink Pair
Special security inks (usually a pair of inks) which look similar in one type of illumination (e.g. in visible light) but show a noticeable difference in another type of illumination (when using a light filter).
a
b
c
Fig. 1. Japan. Passport issued in 2013: back endpaper. Paper substrate
a — data page. Paper substrate; b — the same. Parts of the image are printed in different inks (metameric ink pair). In visible light there is no difference in the colour of image parts; c — the same. Image parts differ in colour. Viewed through a red optical filter
a
b
c
Fig. 2. Qatar. Travel document issued in 2016:
a — back endpaper. Paper substrate; b — the same. Parts of the image are printed in metameric inks. Offset printing; c — the same. A dark profile of a bird is clearly visible. Viewed through a red optical filter
a
b
c
Fig. 3. Japan. Passport issued in 2013:
a — page with an RFID chip. Hybrid substrate. The text DO NOT STAMP THIS PAGE is printed in metameric inks; b — the same. In the text DO NOT STAMP THIS PAGE the words do not differ in colour. White light; c — the same. The words STAMP and THIS differ in colour. Viewed through a red optical filter