Turn on the glowing stamp magic with an ultraviolet lamp

Oct 11, 2010, 1 PM

By Janet Klug

Use ultraviolet light equipment safely

This article discusses the use of ultraviolet (UV) lamps. Shortwave ultraviolet light can harm and burn eyes and skin. Never look at a UV lamp light bulb when it is on. During normal use of the UV lamp, proper UV-blocking eyewear is recommended. Protect skin from exposure to UV rays. Gloves can be worn to reduce the risk, but avoid exposing skin to light from the UV lamp. Children should never use a UV lamp without proper informed adult supervision, and need to be protected from exposure to UV light. Follow all warnings provided by the lamp manufacturer.


Here is a magic trick you can do. Pick a United States stamp — just about any U.S. stamp issued after 1967 will do.

Shazam! Magic happens. The stamp begins to glow an eerie greenish color, perfect for the approaching Halloween season.Using the proper protection for your skin and eyes — as described in the box on this page — grab a shortwave ultraviolet lamp and take both the stamp and the lamp into a dark room. Turn the lamp on and shine it onto the stamp.

So what are these magic lamps and glowing, spooky green stamps all about?

We have to go back about 50 years to the late 1950s, when mail volumes were ballooning for postal services all over the world. The postal services of many nations began experimenting with ways to sort and postmark mail in a faster, more efficient way.

The U.S. Post Office Department turned to private sector companies such as Pitney Bowes for help developing equipment that could locate the stamp and flip the envelope (a process called "facing") so the postmark would be struck in exactly the right place.

In order to do that, the stamp had to send a signal to the machine that effectively said, "I am here."

And that is why stamps got a coating that is invisible — or nearly so — unless subjected to ultraviolet (UV) light, which, when switched on, makes the stamp glow the eerie greenish color. The glowing process is called "luminescence."

The very first U.S. stamps tested for the effectiveness of the new facing/cancelling equipment did not glow eerie green, but instead glowed a wicked pinkish orange when struck with UV light.

The USPOD set up a test of the equipment and the stamps in the summer of 1963, in Dayton, Ohio.

The stamps involved in the test were the 8¢ Jet Airliner over Capitol airmail stamps (Scott C64a).

An overprint using a phosphor compound called "taggant" was applied to the airmail stamps that would be sold primarily in the Dayton area. The taggant was invisible to the naked eye, but glowed pinkish orange when the new high-speed facer-canceller equipment switched on the UV light.

The glow was picked up by the equipment, which flipped the airmail letter and applied a cancel at lightning speed. The test was successful. More successful tests were conducted, leading to the point where today, most commonly used U.S. stamps have taggant added and are thus referred to as being "tagged."

There is a good amount of science in the process of triggering facer-canceller equipment using UV light that senses the glowing material on a postage stamp. That luminescent glow can be either phosphorescent or fluorescent.

A phosphorescent taggant will continue to glow for a short time after the UV light is turned off. When a luminous (glowing) stamp ceases to glow immediately after the UV light is turned off, it has a fluorescent taggant.

The fact that you cannot see most taggants with the naked eye makes collecting and identifying tagged stamps a little more challenging. And yet, all you need is a UV lamp — and the proper protection for your skin and eyes.

Subscribers to Linn's receive a discounted price on a dual-wave UV lamp by ordering through The dual-wave feature means that the lamp provides both longwave and shortwave light. The shortwave light is used to see most tagging. Longwave light is useful when checking for thins, repairs or other kinds of damage or alterations to stamps or covers, and for detecting tagging on some stamps from other countries.

To check luminescence with a UV lamp, set out the stamps you want to check in a work area that can be darkened.

Once the stamps are arranged on the work surface, turn off all the lights in the room and, if daylight is a problem, draw the drapes. Turn on the UV lamp. Make your observations quickly, and jot them down. Little sticky notes work perfectly because they will stick to the work surface rather than float to the floor on an errant breeze.

When the observations have been made and noted, switch off the UV lamp and turn on the ordinary lights. Working in short spurts is better for your eyes and will help keep the UV lamp in good operating order for a longer period.

One fun aspect of collecting tagged stamps is that many varieties, freaks and errors have occurred in the tagging process. These varieties, of course, cannot be detected unless the stamp is viewed with a UV lamp, so you might have rare and interesting stamps masquerading in your albums as common varieties.

Tagging can be shifted, splashed, smeared or missing. It can appear in blocks, bars, patterns or all over.

The U.S. Postal Service has had some fun of its own by adding creative design elements to the tagging process in some instances, such as the glowing flags in the 33¢ Stars and Stripes pane of 20 issued in 2000 (Scott 3403), and the star pattern that matches the stars in the center of the 45¢ Universal Postal Union stamp from 1999 (Scott 3332).

A 33¢ Easton Flag stamp from the Stars and Stripes pane (Scott 3403j) is shown photographed under UV light in Figure 1.

The United States is not the only country using facing/cancelling machines and tagged stamps.

Canada's tagging is extraordinary. If you take a handful of tagged Canadian stamp into a dark room and shine UV light on them, they will nearly light up the room with a brilliant yellow glow, most of which will be in bars along the two sides of the stamps, or in a frame that goes all around the outer edges of the stamps.

Many Australian stamps glow pinkish under UV light, while Hong Kong stamps are a little brighter yellow but nowhere near the brilliant yellow from Canada.

Hungary uses stamp paper impregnated with luminescent materials. The paper is very white and glows brightly under UV light in the unprinted areas of the stamp.

Figure 2 shows one stamp each of Canada, Hungary, Hong Kong and Australia glowing under UV light.

Stamp tagging and the corresponding high-speed machinery used to cancel mail is now old but still effective technology. Using luminescence to properly flip and cancel mail is both a neat trick and a real treat.

Just be careful with those eerie green glowing stamps when the lights are out.