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 cancelling 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.

postage stamps ultraviolet

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 US the first phosphors used for automatic stamps sorting show a characteristic orange glow, just in UV shortwave light (254 nm).

postage stamps ultraviolet

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.

postage stamps ultraviolet

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 common used for automatic sorting.

postage stamps ultraviolet

US postage stamp coated with green glowing phosphor (shortwave UV).

postage stamps ultraviolet

French postage stamp coated with green glowing phosphor bars (shortwave UV).

Phosphors supplemented paper

Some Countries, such as Republic of San Marino, use a paper supplemented with phosphors.

postage stamps ultraviolet

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 suggest an ink containing madder lake [6].

postage stamps ultraviolet

Italian postage stamp showing UV fluorescence suggesting an ink containing madder lake.

Interestingly, the Colombian stamp’s red shows the same behavior of the AIC Photo target red ink, both infrared and ultraviolet fluorescence.

postage stamps ultraviolet

Colombian postage stamp. The red pigment shows both infrared and ultraviolet fluorescent such as the AIC Photo Target red ink.

 


pigments checker v2 vsPigments Checker is for photographers, conservators and scientists interested in technical documentation of paintingss. It has 54 swatches of historical pigments designed for infrared photography, ultraviolet photography and other technical photographic methods for art examination. Check it out!

Pigments Checker is a collection of 54 swatches of his­tor­i­cal pig­ments that have been applied using gum ara­bic as a binder on a cel­lu­lose and cot­ton water­color paper, acids and lignin free. This paper is not treated with opti­cal bright­en­ers, it’s slightly UV flu­o­res­cent, and it reflects IR. Two cross-hair lines, 0,2 mm (ver­ti­cal) and 0.4 mm (hor­i­zon­tal) are printed on each swatch of paper before the appli­ca­tion of paint, in order to have a means to eval­u­ate the pig­ments’ trans­parency in the IR and IRR imag­ing. Among all the pig­ments and their vari­eties ever used in art these pig­ments col­lec­tion select the most used ones from antiquity to early 1950’.


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.

[4] http://www.linns.com/

[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.

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