Tagging (stamp)

The luminescent features of the stamps are generally invisible or barely visible to the human eye in normal illumination.

The luminescent substance ("taggant") can be printed over the whole surface of the stamp, the main design, the margins only, single bands or bars or other patterns, or can be added to the paper itself.

[1] It is achieved by adding optical brighteners that usually re-emit light in the blue region of the spectrum, making the paper appear whiter by compensating a perceived deficit in reflected colours of these wavelengths.

In 1972, fluorescent general tagging was introduced, initially as vertical bars, now normally on all four sides of the stamp.

[3] Deutsche Bundespost started issuing stamps on fluorescent Lumogen paper in 1960 in connection with trials for automated mail processing in the Darmstadt area.

Luminescent tagging has been added to postage stamps of the United Kingdom since the Wilding issues of 1959 in the shape of vertical bands.

[6] Due to the presence of optical brighteners in many printing papers, phosphorescent materials were chosen for stamp tagging in the UK.

Red light was used for this purpose, giving a good contrast to ordinary writing ink colours and enabling machine reading of postcodes.