©Lin Yangchen


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The cross-sectional structure of paper has been studied widely with both optical and electron microscopy. Papermaking methods influence the fibre network morphology and strength of the paper (e.g. Joelsson et al. 2020), while starch distribution (Pigorsch et al. 2013) and the effect of watermarks (Watkins 1990) have been among the many variables of interest. Investigators have also developed statistical methods for analyzing fibre arrangement (e.g. He et al. 2004).

In art conservation, cross-sections of paper and paint are often excised from historical works and mounted in epoxy (see Derrick et al. 1994) for examination of layer composition and order of application of pigments (e.g. Butler 1970, 1973, 1984), as part of artwork characterization, authentication and attribution.

To the author’s knowledge, cross-sectioning has never been done on postage stamps because it ruins the stamp. It is however feasible to do on relatively common stamps with existing damage. One sample of each of the four main paper types of the coconut definitives was sandwiched between two microscope slides held together with the fingers, and a cross-section with minimal artifacts was made with a fast and smooth swipe of a freshly unpackaged vintage Gillette Nacet razor blade along the edge of the glass (an ion beam cutter was not available).

The samples were held vertically between two microscope slides under the author’s ‘Special Forces’ Olympus BHSP microscope and examined with incident illumination. Cross-polarized light was used, which cut out glare from surface scattering.



Mint specimens of (top–bottom) chalky paper and two locations of different thickness (144 μm and 84 μm as measured) on the same stamp of rough paper. They look like bread with orange marmalade, complete with gas bubbles. The boundary between the chalky coating and the underlying fibre network is indistinct, since the liquid coating mixture would have seeped into the paper on application. Minimal percolation (about 10 μm) of the expertly formulated ink ensured a crisp print. The gum on this example of chalky paper is about 50 μm thick.

 
 
ImageJ extended-depth-of-focus stacks of (clockwise from upper left) chalky, substitute, striated and rough papers. The localized depression visible in the striated paper may be from one of the stria or from the watermark. The chalky paper was sectioned crosswise while the rest were sectioned lengthwise so the orientation of the grain is different with respect to the cut; direct comparisons should be made with caution.


References

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