Technology and art often combine in philately. The art aspect is obvious to the naked eye. But sometimes the technology is invisible, as in the case of fluorescent stamps.
Beginning in the 1960s several countries around the world, most prominently those in Scandinavia, employed a curious property of certain compounds in ink.
They used the ability of some molecules to glow under the influence of UV light. Shining an ultra-violet light on those materials causes them to produce variously colored light, sometimes even after the light is removed. Under those conditions, the phenomenon is called phosphorescence.
That property allowed engineers to develop sensors that could detect the presence and orientation of stamps on envelopes. That makes possible an automated system in which machines ‘sense’ where the stamps are, rotate the envelope to the needed position and automatically sort and postmark.
The technology was so efficient that the socialist government of Sweden in the 1970s stopped using it so more people would be required to process mail. As a result, certain issues from that country are now considered relatively rare, and thus a valuable collector’s item.
In order to find and research those stamps, collectors can employ a simplified version of the same technology used by the postal systems around the world. All you need is a good UV light source and a slightly darkened room.
Along with postmarks across stamps, UV can allow the collector to discover interesting information on covers (envelopes, etc) and similar postal materials. The papers themselves vary, sometimes giving off a yellowish light, other times green-blue.
These differences can help identify the year and location of the issue. Finnish catalogs in particular are helpful for research, but catalogs exist for Danish, Norwegian and Swedish issues too.
That fluorescent property can be altered from its original condition by aging, soaking and other causes. Keep in mind during research that the eye is a better color comparer than it is an analyzer. So, it can be helpful to have an issue side by side with another.
Also, know that there are different kinds of UV light – which vary by wavelength. Some materials fluoresce at longer wavelengths, others at shorter ones. So, you may need more than one lamp, or one with the ability to change settings. Scandinavian issues all use long wavelength inks, but many other countries use short wavelength material.
During the examination take care not to expose your hand to UV radiation for long periods. It’s the UV in sunlight that produces sunburn and UV lights can produce the same effect.
A momentary skin exposure is harmless, but you should never look into the UV light. The lens of the eye will focus UV light and the cells in the eye are extremely sensitive and can be permanently damaged. But used wisely, UV light is a safe and effective tool to add to your philatelic toolkit.