How to Detect Fluorescence, Phosphorescence and Scandinavian Philately
Understanding fluorescence differences in Scandinavian stamp papers is a rather technical subject, but those who know some basic information about it can pretty quickly learn how to detect fluorescent papers.
Stamps on phosphorescent reactive paper appeared to enhance mail processing productivity and improve the brightness of papers and inks used to print stamps. Fluorescence means reactivity of a substance under ultra-violet light. Phosphorescence has the same effect, but the only difference is that the reactivity is preserved for some period of time after the light source is no longer present.
In philately, these two terms have often been used as synonyms and catalog and album makers of different countries may use them variously. In practice, it is important for philatelists to know whether a reaction is visible when the stamp is viewed under ultra-violet (UV) light.
In the early 1960s post offices were looking for new technologies that would allow canceling and sorting the increased volume of mail. And this is the time when the idea of using stamps that reacted under ultra-violet light appeared. Due to UV-reactive paper or coating automated facer and canceler equipment could quickly detect the side and corner of the envelope with the postage, rotate the envelope as required, and then place the cancellation properly on the stamp. This improvement resulted in huge labor savings.
Also post offices started using fluorescent inks for bar-coding mail sorting data. After a bar code was imprinted, the machine could easily sort and resort the mail. With UV-reactive ink used, the machines could quickly and unmistakably detect the bar code.
For several decades papermakers used to add "paper whiteners" to make their paper look brighter at the daylight. Often, the inks printed on brighter papers became more vibrant and featured more contrast. The "paper whiteners" are usually UV reactive and may look white, bluish or yellowish when viewed under UV light. Such paper is a different from ordinary stamps paper and is thus catalog-listed and is valued by specialists.
The Scandinavian catalogs for Sweden have not listed the so-called whitened papers although issues from the 1950s to the 1980s do exist.
When referring to either fluorescent or phosphorescent stamps catalog publishers and album makers just mean reactivity under UV light while the terms "ordinary paper", "nfl", and "non fluor" are used for stamps which do not react under UV light.
Typically reactive Scandinavian stamps when under UV light are distinguished by white, bluish or yellow colors while stamps of other countries may be orange and sometimes green. The intensity of the color can mean various coatings or papers. Different color can also be the result of extended exposure to light, aging, soaking to remove stamps from envelopes, or contact with other reactive materials. It should be noted that soaking stamps may decrease the fluorescence or even change fluorescence from the other stamps that were soaked at the same time.
When it comes to Denmark, there are many fluorescent stamps of the 1960s featuring both white and yellow fluorescence. As for Norway, even slight differences in appearance are cataloged by Norgeskatalogen.
When trying to identify a UV-reactive stamp make sure you compare both issues in the same viewing. Keep in mind that the terminology may be misleading: it is not a problem to differentiate the "yellow fluor" and "white fluor" when you see both at the same time, but you may feel confused when seeing only one at a time as the "white" may often seem yellowish and visa versa.
All Scandinavian UV-reactive stamps require the use of long wave ultra-violet light for viewing. But the stamps of the U.S. and many other countries must be viewed using short-wave ultra- violet light. So if your collection includes only Scandinavia, you don’t need to splurge on expensive dual light source, but if you collect other countries as well, it will be your must have.
Do remember that short-wave UV light causes much more harm than long-wave. UV light causes "sunburn" and can seriously hurt the eyes so avoid looking into a UV light and reduce the time the light is on to minimum. Make sure you cover exposed skin and never hold stamps in hand when the light is on. The light shouldn’t be used in the room with reflective surfaces because reflected UV light is as harmful as directed light. Never use the light when other people are present.