As a kid, I used to collect stamps. Cleaning up my place I just found my little collection and I thought to give it a quick Technical Photography glance. Postage stamps are a form of art, no doubt about it. I recall how much I was fascinated by those little images. Technical examination of postage stamps is used for their authentication [1, 3], as it’s pleasantly told by Brestow in Fakebusters II [2]. resources on stamps collecting and their technical examination are also available online [4, 5].
Stamps and Phosphors
In the late 50s postage stamps, in countries such as UK and USA, started to be coated with phosphors in order to make postal sorting and canceling machine automatic. Phosphor ink is invisible to the naked eye but the sorting machines can see it.
There are two Ultraviolet wavelengths used for the examination of stamps. Phosphors are best viewed in shortwave ultraviolet light (254 nm). Longwave light (365 nm) is used to detect alterations, damages and repairs. I selected some of postage stamps out of my collection and took some multispectral images.
Visible, UV longwave (365 nm) and UV shortwave (254 nm) Fluorescence Photography. A selection of postage stamps out of my collection, representing a number of countries and periods.Orange glow
In the US the first phosphors used for automatic stamps sorting show a characteristic orange glow, just in UV shortwave light (254 nm).
US postage stamp coated with orange glowing phosphor. Only the shortwave UV light allows seeing the orange glow of the phosphor coating.Yellow glow
Used by Countries, such as Canada, Mexico, and Switzerland, the yellow glow from this phosphor is visible both in longwave and shortwave UV light.
Canadian postage stamp coated with yellow glowing phosphor. Both longwave and shortwave UV light allow seeing the yellow glow.Green glow
Green glowing phosphors are currently the most commonly used for automatic sorting.
US postage stamp coated with green glowing phosphor (shortwave UV). French postage stamp coated with green glowing phosphor bars (shortwave UV).Phosphors supplemented paper
Some Countries, such as the Republic of San Marino, use a paper supplemented with phosphors.
The Republic of San Marino uses paper supplemented with phosphors.Stamps and Pigments
Analytical identification of stamps’ pigments is part of their authentication process. The UV fluorescence of an old Italian stamp suggests an ink containing madder lake [6].
Italian postage stamp showing UV fluorescence suggesting an ink containing a madder lake.Interestingly, the Colombian stamp’s red shows the same behavior of the AIC Photo target red ink, both infrared and ultraviolet fluorescence.
Colombian postage stamp. The red pigment shows both infrared and ultraviolet fluorescent such as the AIC Photo Target red ink.
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References
[1] T. D. Chaplin, A. Jurado-Lopez, R. J. H. Clark, D. R. Beech “Identification by Raman microscopy of pigments on early postage stamps: distinction between original 1847 and 1858–1862, forged and reproduction postage stamps of Mauritius” J. Raman Spectrosc. 2004; 35: 600–604.
[2] Bristow M. “Scientific Detection of Philatelic Forgeries” Fakebusters II, Scientific Detection of Fakery in Art. SPIE and McCrone Research Institute: Chicago, IL, 2001; 55–65.
[3] Chaplin TD, Clark RJH, Beech DR. “Comparison of genuine (1851–1852 AD) and forged or reproduction Hawaiian Missionary stamps using Raman microscopy” J. Raman Spectrosc. 2002; 33: 424.
[5] http://www.filatelia.fi/forglinks/index.html
[6] R. Chenciner “Madder Red: A History of Luxury and Trade” Routledge, Reprint edition (2011). Page 201.
[7] J. Sharkey “Chemigry of Postqe Stamps: Dyes, Phosphors, Adhesives” Chemistry on Stamps, Volume 64 Number 3 March 1987.
interested job, i´ll try to do the same analysis whit my husband´stamp collection, then i let you know
regards
Carolina
Hi Carolina, always nice to hear from Cile! Ciao!
On the basis of Elvis stamps alone this deserves many props and shout-outs!
ahaha. It probably suited many Elvis fans.
Great article! I never knew so much about stamps.
Would like to know if there is a flatbed scanner that uses a shortwave UV light as a light source.
Would like to scan stamp tagging or lack of tagging (untagged errors) and input the image into a keynote (powerpoint)
presentation.
Current slow way is to use a light box with a uv light and camera. Then download.
Please comment, any info would be helpful.
Thanks, Dan
Hi Dan,
I don’t know of any scanner like that. On the other hand, I think it is pretty possible you could build one on your own. You can use the digital camera instead of the scanner and put the stamps on a glass and on the other side the camera and the UV light. Never done this but it is reasonable it will work and worth to try if you need to image a large number of stamps. But it also makes sense just to have the camera and the light on a desk on a copy stand and just shoot the stamps. it pretty fast.