Identification Series: Luminescence and UV Lighting
Jan 6, 2024 14:24:38 GMT
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Post by ClassicPhilatelist on Jan 6, 2024 14:24:38 GMT
For those of you who know me, you will know that I tend to focus on classics (hence the "Classic Philatelist"). But the topic of tagging recently came up, and I do think this is a great point to talk about.
First, tagging is the process of applying a specialized ink (that is usually invisible or near invisible) on a stamp for the purpose of directing mail with automatic sorting machines.
There are two types of tagging: Florescence and Phosphorescence. Each responds to a different wavelength of UV lighting, so for detection, the right wavelength light is required or the luminescence won't be visible.
Phosphorescence will luminesce at a wavelength of 254nm - 266nm (nanometer), while Florescence will luminesce at 359nm - 380nm. If your UV light is not within these ranges, you will see nothing. So first, you need to determine what type of UV light you need to see the result, and then apply that UV source to the target. Fluorescent tagging on stamps, unlike phosphorescent tagging, emits light only while under ultraviolet light and stops glowing immediately when the light source is removed. Phosphorescence however, may continue to emit visible light for serval second (5 to 20) after the UV light source is removed. (However, I would highly suggest using these light sources in a dark environment, like a large closet or a room that can be darkened with blackout curtains, or in a basement). The florescent and phosphorescent emissions may be seen in lit environments, but they are diminished. If that's not possible, then make the room as dark as possible, and shield other light as much as possible.
There are both corded and battery powered UV lights available, in both LED and florescent stick. Light is light, and the type of source is irrelevant, so long as it emits light in the correct wavelength.
Florescence was the first to appear, in 1960. The first postage stamps to use fluorescent tagging were issued by Germany. These stamps were printed on fluorescent Lumogen paper as part of trials for automated mail processing. From 1961 onward, fluorescent paper was generally used for stamps of Deutsche Bundespost and Deutsche Bundespost Berlin. The first U.S. postage stamp to use fluorescence was the 5-cent Washington stamp, part of the Prominent Americans series, issued in 1967.
The first stamp to use this technology were the Canadian Cameo Issues in 1962. The type of tagging used in this instance was phosphorescent inking. The first U.S. postage stamp to use phosphorescent tagging was issued on August 1, 1963. The C64a first issued at Dayton, Ohio, was part of an experiment by the U.S. Post Office to speed up mail sorting and cancellation using luminescent stamps. The stamp was overprinted with a special compound, a taggant, that made it glow pinkish orange under ultraviolet light, allowing the sorting machinery to detect it efficiently.
As luminescent tagging progressed, it has appeared in many forms. Some entirely cover the stamp. Others only part or parts of stamps. And some, the ink that makes up the design itself is used as the luminescent tag.
The field of added tagging to stamps introduced the possibility of a new type of "error" stamp. Since the tagging applied is transparent to invisible to the naked eye, the possibility of untagged stamps to slip unnoticed to inspectors also resulted.
Examining the Stamp:
In order to examine a tagged stamp, the stamp must be removed from any enclosure (i.e. you cannot check for luminescence through a plastic cover; it must be out of the mount, or hingeless album page, graded encasement, etc.). Best results for luminescence testing is with a black background. (The back of an old black stock page, or a dealer card make a great background.)
Darken the room as much as possible, as mentioned. It's ok to have a light you can turn off or on easily so you get set up, switch the light out, turn on your UV source, and hold it near the stamp, starting at a 90 degree angle about 10mm (1/2 inch).
This first image shows two stamps side-by-side (1341 and 1339) under normal light.
This second image is of the same two stamps, with a 254nm UV light exposure.
It is difficult to photograph luminescence and the image above at right will luminesce more yellow-green than is pictured. But the difference is quite clear between the stamps in the first image, versus the stamps in the second image. These were applied with a 254nm UV light.
Another example below is more difficult to see.
Compare the above to the image below.
The stamp at left is also illuminated under 254nm UV. Note that the shade is red. It is sometimes difficult to differentiate this if there is strong natural lighting. (This is a function of red light waves, which are easily disturbed by normal light. So this is a case where the darker the environment, the better. I actually covered my camera entirely with a cloth to take this image).
Modern stamps (1990 and later) are often very bright in their luminesce, as is demonstrated in the next two images.
This image is normal lighting.
And this is the image with 254nm UV light is applied.
This is a great example of where the luminescent application after stamp printing is applied is visible, if you look for it in the right light.
In this image, the sheet is tilted slightly into reflected light, and the outside line of the luminescent coating is visible.
Just outside the die cut, the coating is visible.
Just to recap, the visibility of luminescent tagging is best viewed in the darkest environment possible, but does not require absolute darkness. In some cases, the coating can be seen on the stamp when turned into reflected light. Some luminescence is achieved with a luminescent paper, instead of a coating, these usually being phosphorescent papers.
First, tagging is the process of applying a specialized ink (that is usually invisible or near invisible) on a stamp for the purpose of directing mail with automatic sorting machines.
There are two types of tagging: Florescence and Phosphorescence. Each responds to a different wavelength of UV lighting, so for detection, the right wavelength light is required or the luminescence won't be visible.
Phosphorescence will luminesce at a wavelength of 254nm - 266nm (nanometer), while Florescence will luminesce at 359nm - 380nm. If your UV light is not within these ranges, you will see nothing. So first, you need to determine what type of UV light you need to see the result, and then apply that UV source to the target. Fluorescent tagging on stamps, unlike phosphorescent tagging, emits light only while under ultraviolet light and stops glowing immediately when the light source is removed. Phosphorescence however, may continue to emit visible light for serval second (5 to 20) after the UV light source is removed. (However, I would highly suggest using these light sources in a dark environment, like a large closet or a room that can be darkened with blackout curtains, or in a basement). The florescent and phosphorescent emissions may be seen in lit environments, but they are diminished. If that's not possible, then make the room as dark as possible, and shield other light as much as possible.
There are both corded and battery powered UV lights available, in both LED and florescent stick. Light is light, and the type of source is irrelevant, so long as it emits light in the correct wavelength.
Florescence was the first to appear, in 1960. The first postage stamps to use fluorescent tagging were issued by Germany. These stamps were printed on fluorescent Lumogen paper as part of trials for automated mail processing. From 1961 onward, fluorescent paper was generally used for stamps of Deutsche Bundespost and Deutsche Bundespost Berlin. The first U.S. postage stamp to use fluorescence was the 5-cent Washington stamp, part of the Prominent Americans series, issued in 1967.
The first stamp to use this technology were the Canadian Cameo Issues in 1962. The type of tagging used in this instance was phosphorescent inking. The first U.S. postage stamp to use phosphorescent tagging was issued on August 1, 1963. The C64a first issued at Dayton, Ohio, was part of an experiment by the U.S. Post Office to speed up mail sorting and cancellation using luminescent stamps. The stamp was overprinted with a special compound, a taggant, that made it glow pinkish orange under ultraviolet light, allowing the sorting machinery to detect it efficiently.
As luminescent tagging progressed, it has appeared in many forms. Some entirely cover the stamp. Others only part or parts of stamps. And some, the ink that makes up the design itself is used as the luminescent tag.
The field of added tagging to stamps introduced the possibility of a new type of "error" stamp. Since the tagging applied is transparent to invisible to the naked eye, the possibility of untagged stamps to slip unnoticed to inspectors also resulted.
Examining the Stamp:
In order to examine a tagged stamp, the stamp must be removed from any enclosure (i.e. you cannot check for luminescence through a plastic cover; it must be out of the mount, or hingeless album page, graded encasement, etc.). Best results for luminescence testing is with a black background. (The back of an old black stock page, or a dealer card make a great background.)
Darken the room as much as possible, as mentioned. It's ok to have a light you can turn off or on easily so you get set up, switch the light out, turn on your UV source, and hold it near the stamp, starting at a 90 degree angle about 10mm (1/2 inch).
This first image shows two stamps side-by-side (1341 and 1339) under normal light.
This second image is of the same two stamps, with a 254nm UV light exposure.
It is difficult to photograph luminescence and the image above at right will luminesce more yellow-green than is pictured. But the difference is quite clear between the stamps in the first image, versus the stamps in the second image. These were applied with a 254nm UV light.
Another example below is more difficult to see.
Compare the above to the image below.
The stamp at left is also illuminated under 254nm UV. Note that the shade is red. It is sometimes difficult to differentiate this if there is strong natural lighting. (This is a function of red light waves, which are easily disturbed by normal light. So this is a case where the darker the environment, the better. I actually covered my camera entirely with a cloth to take this image).
Modern stamps (1990 and later) are often very bright in their luminesce, as is demonstrated in the next two images.
This image is normal lighting.
And this is the image with 254nm UV light is applied.
This is a great example of where the luminescent application after stamp printing is applied is visible, if you look for it in the right light.
In this image, the sheet is tilted slightly into reflected light, and the outside line of the luminescent coating is visible.
Just outside the die cut, the coating is visible.
Just to recap, the visibility of luminescent tagging is best viewed in the darkest environment possible, but does not require absolute darkness. In some cases, the coating can be seen on the stamp when turned into reflected light. Some luminescence is achieved with a luminescent paper, instead of a coating, these usually being phosphorescent papers.