©Lin Yangchen
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Postage stamps are almost always conceptualized as a two-dimensional plane. That’s fine if you’re putting together a basic stamp collection. But there comes a time when you have to tell apart two very different stamps that look almost exactly identical on the surface (pun intended) or determine if a stamp has been forged or tampered with. By adding the third dimension, the scope for understanding and explaining previously unexplained phenomena increases dramatically, such as in paper identification and print characterization.
Paper samples for surface profilometry (Lin 2020c).
The stamps were placed under a Keyence VHX microscope and kept flat on the microscope stage with glass slides to prevent curling, exposing just the area of interest. The target area on each stamp was the large uninked area beside the foot of one of the coconut palms. The surface of the stamp was perpendicularly lit, and a photomicrograph was obtained from the reflected light. The microscope takes many micrographs while moving vertically through different focal planes 0.1 μm apart. On each focal plane, only certain parts of the stamp are in focus. The microscope’s software estimated the height of a given point on the stamp by finding the focal plane where the point showed maximal contrast in the image, which indicated the point was in focus.
Aerogramme paper is the roughest, its profiles resembling mountain ranges. Aerogrammes were meant to be as thin and light as possible, so it is not unreasonable to suppose the coating was omitted for that reason. Striated paper, rough paper, printer’s waste and postal stationery card are all on the rough side, but less so than aerogramme paper. The roughness is generally due to lack of a coating and exposure of the fiber network.
The coating of chalky paper makes it less rough than the aforementioned papers on the scale of the fibres, although it can be deeply cratered as in sample Ch2. It turns out that at a smaller scale than the fibres, chalky paper exhibits roughness in the form of granules, but the resolution here is insufficient to capture this.
Substitute paper looks rough, but it's a "slippery rock" kind of unevenness, not the fibrous kind of roughness seen in the uncoated papers. This has a particular effect on its print characteristics.
Of all the papers, the essay paper is the smoothest. The print quality of the essays is very crisp, but should not be directly compared with the issued stamps, as they were lithographed while the stamps were letterpressed.
Meanwhile, the surface of the back of the stamp reveals hidden varieties in a little-documented facet of papermaking, which was first reported by Rein Bakhuizen van den Brink (see van den Brink & Lin in press).
In a papermaking machine, a fine woven sieve drained water from the pulp, leaving a thin layer of cellulose fibres to form the paper. The sieve was woven using standard patterns from the textile industry, and left a faint pattern on the so-called wove paper. At first, a linen or plain weave was used. This left a symmetric diamond hatched pattern on the paper. In the late 1930s, papermakers began to use the stronger twill weave, which left a pattern that was asymmetric in both the angles and spacings.
Most of the pre-war coconut definitives have the linen weave pattern, including those on striated paper and rough paper. The substitute paper from the immediate post-war period also has the linen weave pattern. Surprisingly, the twill weave pattern occurs on the pre-war 30¢, as discovered by van den Brink. There is no straightforward explanation for this, as the 30¢ was not a particularly late printing. As expected, most post-war coconut definitives have twill weave patterns.
Acknowledgements
I am grateful to David Beech, Rein Bakhuizen van den Brink, Julian Tan and Edmond Soh for discussions and technical assistance, and to Keyence Singapore for the use of their equipment.
References
previous section | next section | back to table of contents
previous section | next section | back to table of contents
Postage stamps are almost always conceptualized as a two-dimensional plane. That’s fine if you’re putting together a basic stamp collection. But there comes a time when you have to tell apart two very different stamps that look almost exactly identical on the surface (pun intended) or determine if a stamp has been forged or tampered with. By adding the third dimension, the scope for understanding and explaining previously unexplained phenomena increases dramatically, such as in paper identification and print characterization.
Paper samples for surface profilometry (Lin 2020c).
The stamps were placed under a Keyence VHX microscope and kept flat on the microscope stage with glass slides to prevent curling, exposing just the area of interest. The target area on each stamp was the large uninked area beside the foot of one of the coconut palms. The surface of the stamp was perpendicularly lit, and a photomicrograph was obtained from the reflected light. The microscope takes many micrographs while moving vertically through different focal planes 0.1 μm apart. On each focal plane, only certain parts of the stamp are in focus. The microscope’s software estimated the height of a given point on the stamp by finding the focal plane where the point showed maximal contrast in the image, which indicated the point was in focus.
Aerogramme paper is the roughest, its profiles resembling mountain ranges. Aerogrammes were meant to be as thin and light as possible, so it is not unreasonable to suppose the coating was omitted for that reason. Striated paper, rough paper, printer’s waste and postal stationery card are all on the rough side, but less so than aerogramme paper. The roughness is generally due to lack of a coating and exposure of the fiber network.
The coating of chalky paper makes it less rough than the aforementioned papers on the scale of the fibres, although it can be deeply cratered as in sample Ch2. It turns out that at a smaller scale than the fibres, chalky paper exhibits roughness in the form of granules, but the resolution here is insufficient to capture this.
Substitute paper looks rough, but it's a "slippery rock" kind of unevenness, not the fibrous kind of roughness seen in the uncoated papers. This has a particular effect on its print characteristics.
Of all the papers, the essay paper is the smoothest. The print quality of the essays is very crisp, but should not be directly compared with the issued stamps, as they were lithographed while the stamps were letterpressed.
Meanwhile, the surface of the back of the stamp reveals hidden varieties in a little-documented facet of papermaking, which was first reported by Rein Bakhuizen van den Brink (see van den Brink & Lin in press).
In a papermaking machine, a fine woven sieve drained water from the pulp, leaving a thin layer of cellulose fibres to form the paper. The sieve was woven using standard patterns from the textile industry, and left a faint pattern on the so-called wove paper. At first, a linen or plain weave was used. This left a symmetric diamond hatched pattern on the paper. In the late 1930s, papermakers began to use the stronger twill weave, which left a pattern that was asymmetric in both the angles and spacings.
Most of the pre-war coconut definitives have the linen weave pattern, including those on striated paper and rough paper. The substitute paper from the immediate post-war period also has the linen weave pattern. Surprisingly, the twill weave pattern occurs on the pre-war 30¢, as discovered by van den Brink. There is no straightforward explanation for this, as the 30¢ was not a particularly late printing. As expected, most post-war coconut definitives have twill weave patterns.
Acknowledgements
I am grateful to David Beech, Rein Bakhuizen van den Brink, Julian Tan and Edmond Soh for discussions and technical assistance, and to Keyence Singapore for the use of their equipment.
previous section | next section | back to table of contents