Magnetic detection

During bank notes printing they use dyes with magnetic properties that appear after adding some ferromagnetic components into a dye. Such a dye can be detected by means of magnetic image visualizers or by testers with magnetic head. They often print serial numbers or fragments of metallographic picture with a magnetic dye.

A monochromatic picture may be done with two dyes of the same hue tone but with different magnetic properties making a discrete distribution of magnetic dye on the picture (for example, a black guilloche frame on USA dollars' face of series of issue after 1988).

Expert's practice testifies that a magnetic picture is not imitated in the over-whelming amount of counterfeits. An exclusion is counterfeit USA dollars (so called "supercounterfeits") having a magnetic picture distribution slightly different from authentic bank notes.