Mark Stockburger - Administrator
Al Gore - Contributor
As the postal service grew and evolved, the speed and efficiency of the cancelling process became paramount. Automated cancellers required the mail piece to be properly orientated so the cancel could be applied correctly. As a repetitive task, this was well suited for a technology solution. The US Postal Service began experimenting with fluorescent compounds sometime around 1954; these compounds were primarily phosphor based and glowed when exposed to ultraviolet (UV) light. By applying the fluorescent compounds (called tagging) to the stamp, special equipment could then detect the corner the stamp was in and orientate the mail piece properly for cancelling. Tagging is typically invisible to the human eye.
The first regular production US stamp with tagging was the 1963 8¢ Airmail issue #C64a and was followed with the first commemorative stamp tagged stamp: 5 cent City Mail Delivery issue #1238. Since that time hundreds of US stamp have been issued with tagging and some stamp were issued in both tagged and un-tagged versions. This was sometimes due to a stamp first being issued un-tagged but later in the production run tagging was added. These were not ‘errors’ but rather just normal varieties of the same stamp issue. But note that ‘tagging omitted’ errors do exist for stamp which were only issued in tagged form.
The postal service used three basic methods for making a stamp tagged; tagging could be applied on top of the printed stamp, it could be mixed with paper pulp, or it could be mixed with the printers ink. Tagging also was applied to the stamp in several different ways. One method was a continuous tagging where the taggant was applied from edge to edge of the sheet of stamps. Another method is called block tagging where there are untagged gaps between the tagged areas. Block tagging was used to prevent the abrasive taggant from prematurely wearing the perforating pins.
To detect tagging on US stamp an ultra-violet (UV) light is essential. Many UV lights have both short-wave filter or a long-wave filter and these are ideal for most collectors; the short wave detects the type of tagging and long-wave detects paper types used for printing a stamp.
This Stamp Smarter community project tagging database represents the largest online resource for anyone who is interested in this fascinating aspect of philately. To view or search database please click on the button above.