US Tagging & Luminescence Database

Mark Stockburger - Administrator
Al Gore - Contributor
Don Denman - Developer

Types of UV Light
Ultraviolet light (UV) is form of the electromagnetic spectrum that is adjacent to and greater in energy than visible light. The ultraviolet spectrum ranges from 180 to 400 nanometers (nm) and is divided into three categories: shortwave, mediumwave, and longwave.

Shortwave UV light extends from 180 to 280 nm with a peak in energy at about 254 nm. For best results the shortwave UV source should be appropriately filtered (not  unfiltered). Ultraviolet equipment that produces light in the shortwave region is typically used for toxicology, fluorochemistry, and germicidal applications. It is also used for identifying US stamp tagging.

Mediumwave UV light extends from 280 to 320 nm with a peak in energy at about 312 nm. Mediumwave UV lamps are generally used in electrophoresis documentation procedures and to identify minerals by their fluorescent response.

Longwave UV light, or black light, extends from 320 to 380 nm with a peak in energy at about 365 nm. Longwave UV is often used in leak detection (in conjunction with fluorescent dyes) and is useful for mineral studies. This is best for identification of Great Britain Machins and for US papers.

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.