IR-detection

In modern bank notes they widely use dyes which are perceived at sight as dyes of the same colour but have different reflection in infra-red spectrum range. Such an effect is called as IR-metamerism of dyes. If a drawing is made with two dyes identical in hue but different in properties, than in IR-range of spectrum one will see only a part of the whole drawing corresponding to the zone coated with the dye reflecting IR-rays.

By now, there has not been revealed any imitation of such an effect on counterfeited bank notes. It is technically impossible to imitate IR-protection by a primitive way, while the use of special equipment makes counterfeiting too expensive and economically unprofitable.

Some parts of imprint on some counterfeit bank notes are still visible in IR-light. However, these fragments are made with dyes that differ in hue from dyes in other elements of the picture, that is why one can say that these dyes do not have metamerism properties though they are revealed in IR-light.