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Fluorescence, Phosphorescence, Ultraviolet Light, and Scandinavian Philately
by Jay Smith & Associates

An important note of caution: Ultraviolet light causes "sunburn" and can do serious damage to the eyes. Never, never, never look into a UV light source. Minimize the time the light is on. Cover exposed skin. Do not hold stamps in hand while using light. Avoid using light where there are reflective surfaces; reflected UV light can cause just as much harm as direct UV light. Do not use while other people are present. Short-wave UV light is much more harmful than long-wave.

Detecting fluorescence differences in Scandinavian stamp papers is a subject about which I receive many inquiries. This can be a highly technical subject, however, armed with some basic information it is relatively easy to master detecting fluorescent papers.

Use of fluorescent or phosphorescent reactive papers for stamps has come about for two basic reasons: 1) increased productivity of mail processing and 2) improvement in brightness of papers and appearance of the inks used to print stamps.

Ultraviolet light (200-400 nanometers) is of shorter wavelength than visible light (400-800 nanometers). Fluorescence refers to the emission of visible light from a substance which is being irradiated with ultraviolet light (sometimes called "black light" because it is not visible to the human eye). Phosphorescence is the same except that the emission of light continues for some period of time after the ultraviolet light source is removed. Ultraviolet light is absorbed by a substance, which has been used either in the stamp paper or to coat the stamp surface. This causes the irradiated substance to adopt an excited electronic state which emits visible light of a longer wavelength than the original ultraviolet light. Why some substances phosphoresce and others fluoresce is a function of the dynamics of the excited state and the molecular structure of the particular substance.

Unfortunately, in philately, the two terms have often been used interchangeably and also tend to be used variously by catalog and album makers operating in different parts of the world. From a practical standpoint, however, all we philatelists care about is whether or not we see an emission of visible light while viewing the stamp irradiated with ultraviolet light.

In the early 1960s, when post offices sought new technologies for canceling and sorting the exploding volume of mail, the concept of using stamps that emitted visible light when irradiated with ultraviolet light came to the fore. Using paper made with or coated with a compound which fluoresces or phosphoresces allows automated facer and canceler equipment to locate which side and corner of the envelope bears the postage, rotate the envelope as required, and then place the cancellation properly on the stamp. This resulted in huge labor savings; so much so that in the 1970s Sweden discontinued the use of fluorescent papers supposedly so that more people could be employed in the process of canceling mail.

Likewise, post offices have used fluorescent inks for bar-coding mail sorting information. Once imprinted with a bar code, the mail can be sorted and resorted by machine. By using an ultraviolet absorbing ink to make the bar code imprint, the machines can more easily see the bar code without being confused by the other markings on the envelope.

Papermakers have, for several decades, added "paper whiteners" to make the daylight visible brightness of their paper brighter. In many cases, brighter papers make the inks printed on them appear more vibrant, add contrast, etc. The "paper whitener" compounds, in actuality, absorb ultraviolet light and emit visible light. When viewed under ultraviolet light, the brightened papers may look white, yellowish, or bluish. The use of such brighteners is typically not for postal purposes. In some case the post offices have been completely unaware that there is more than one version of the paper. Papers that includes such brighteners are different papers compared to those that do not and are thus catalog-listed in most specialized catalogs and are sought by specialists.

Scandinavian catalogs listing Swedish stamps have not done a good job (or any job) of listing the so-called whitened papers. From the 1950s to the 1980s a number of whitened paper issues exist but are not listed by the specialized catalogs. It is a great opportunity for further research.

In the case of Denmark, a number of the fluorescent stamps of the 1960s exist with both white and yellow fluorescence. However, I am not aware of any catalog that recognizes this fact. In contrast, very minor differences in the fluorescent appearance of Norwegian stamps (the result of different papers from different papermakers) are all cataloged by Norgeskatalogen.

When catalog publishers and album makers refer to either fluorescent or phosphorescent stamps they are, as a practical matter, simply referring to emission of visible light when viewed under ultraviolet light. In Scandinavian philately, I am not aware of any stamp issues which have been issued in both fluorescent and phosphorescent versions.

The terms "ordinary paper", "nfl", and "non fluor", all refer to stamps which do not emit visible light upon irradiation with ultraviolet light, or for which the emission is dull or insignificant.

The visual appearance of Scandinavian stamps which fluoresce or phosphoresce may range from bluish to white to yellow. (Stamps of other countries also use orange and green, and probably other colors too.) The difference, intensity, or texture of the color can signify different papers or coatings. Differences can also be the result of aging, soaking to remove stamps from envelopes, extended exposure to light (particularly ultraviolet light), contact with other fluorescent or phosphorescent materials (including other stamps, particularly in the case of Canadian stamps). When the difference signifies a different paper, it usually results in a listing in the specialized catalogs; modern Finnish and Norwegian definitive stamps are good examples of well-researched listings.

It must be emphasized that soaking stamps (to remove them from envelopes) may result in the reduction or loss of the fluorescent coating. Soaking fluorescent stamps (or the envelope paper they are on) with non-fluorescent stamps may result in the transfer of fluorescence to a non-fluorescent stamp. For this reason it is a good idea to soak stamps only in small batches. It may also be helpful to pre-check the envelope paper they are on for any that are strongly fluorescent; it is best to soak those separately.

When attempting to identify which of the different possibilities of a fluorescent stamp issue you have, it is usually important to compare both issues in the same viewing. In many cases, particularly comparing examples of whitened papers to fully fluorescent examples, seeing just one of the two possibilities will result in more confusion than answers. Furthermore, the terminology may be relative: the difference between "white fluor" and "yellow fluor" may be obvious when you see both at the same time, but the may be very misleading if you see only one copy of the stamp.

In Scandinavian philately, all fluorescent stamps must be viewed using long wave ultraviolet light. In contrast, the stamps of many other countries (including the U.S.) require the use of short wave ultraviolet light. If you only collect Scandinavia, you only need the less costly long wave light. However, if you collect other countries as well, you will probably be better off buying a dual light source.

There are many sources for UV lights, including both philatelic supply houses and mineral "rock hound" shops. I offer a handy and inexpensive battery-operated long wave UV light which I use myself.

If you are seeking a dual (long wave and short wave) UV light, check with the philatelic supply houses. They have a variety of sizes and models.

After initial publication of this article in my March 14, 2002, Scandinavian Philatelic E-News, I was pleased to receive valuable suggestions and additional information from Dr. John Grunwell, a philatelist and an organic chemist with a professional interest in the field of photochemistry. Holding a Ph.D. from MIT, Dr. Grunwell is a well-published Full Professor of Chemistry at Miami University and has taught photochemistry as a special topic at the graduate level.

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