©Lin Yangchen

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Postage stamps are 99% biology. Cellulose makes up almost all of a stamp's mass and volume, but few have ventured into the jungle of plant fibres below the printed surface. Thus Spake Cocographia, the author's very own journey through the hidden universe of subphilatelic particles, after Robert Hooke's Micrographia of 1665.

In the early 20th century, the Crown Agents specified that paper for letterpressed stamps should be mainly rag (Faux 1986), which was highly durable and absorbed ink well. After World War II, the Crown Agents and the printers agreed on a composition of 80% rag, which would give a strong paper (Faux 1986, Glazer 2004). Rags and textile production waste made up much of the fibre supply in the 1940s and 1950s (Tullis Russell 1950). The remaining 20% of the paper comprised sulphite-treated softwood pulp, esparto grass and a plethora of chemical additives (Glazer 2004). The sulphite process removes lignin, which would otherwise make the paper prone to acid hydrolysis. Almost pure cellulose is obtained. Glazer (2004) provides a detailed account of how the paper for the British colonial stamps was reportedly made.

Cellulose, the building block of one of mankind’s most important inventions.
Paper was invented in China around 100 bc.

During the coconut definitive era, De La Rue used machine-made wove paper from Wiggins, Teape & Co., made at Stowford Paper Mill near the southwestern tip of England (Glazer 2004, Yendall 2008). At least during the George V period, the paper was thought to have been plate-glazed between rollers to smoothen the surface before it was delivered to De La Rue (Fernbank 2013).

Photomicrographs of the gumless backs of used coconut definitives on the four main paper types, under a 20× plan apochromatic objective with transmitted Köhler illumination and extended-depth-of-field stacking. By looking behind the stamp, one can examine the fibre network in situ without the coating and without damaging the stamp. Clockwise from upper left: pre-war chalky paper, striated paper, rough paper, post-war chalky paper. They appear qualitatively similar, fibrously speaking.

For fibre extraction, the sacrificial stamps were bisected diagonally. One half was meant for fibre analysis while the other was to be kept as a record. Eventually both were repulped but a corner was snipped off each stamp and kept. The corners contained printed areas to aid in verification of paper type. 1, pre-war chalky paper; 2, 1941 striated paper; 3, 1941 rough paper; 4, post-war substitute paper (British Military Administration); 5, post-war chalky paper (Queen Elizabeth II for latest possible sample). Common values were chosen that were in reasonably good condition without too much fungal deterioration. They were all different colours to minimize the chances of a mix-up. Repulping follows Donaldson (2009), Barwis (2013) and Katz (2015) with modifications.

The bisect was torn into small pieces by hand to avoid cutting the fibres. Any stamp hinges were removed. The author encountered unexpected difficulties trying to push the bits together with his finger: static electricity generated during tearing made the paper fragments come alive, jumping about like uncontrollable grasshoppers.

The Coconut Reactor. Chinese double-boiled coconut essence with distilled water purchased from the supermarket. To minimize alteration of the fibres, I decided not to use sodium hydroxide or other repulping chemicals.

True to 007, the test tubes were periodically shaken, not stirred. A rubber bung was used to stopper the mouth and permit vigorous agitation. Maceration overran into dinnertime, and the author moved indoors with the eggs, oatmeal and a glass of ice-cold lime soda as stir-frying of petai started outside. Finally, everything was allowed to settle and most of the water was decanted off. Then the test tube was shaken and the cloudy water was droppered onto a microscope slide.

Makeshift al fresco laboratory in the author's kitchen. "Coconut broth" is being deposited and evaporated for five cycles on the slide on the hot plate ("Milk" setting, 60° C) to concentrate the fibres.

Chemicals and glassware were sourced from one of the very few remaining small-enterprise scientific suppliers tucked away in an industrial park in the outskirts of the city, where you can walk in and pick items off the shelves. You pay cash and they wrap it up in old newspapers, like fish at the market.

"Cryogenic" preservation of "coconut broth" in the kitchen fridge. The screw-top tubes used to hold live cultures of dinoflagellates in one of my undergraduate research projects.

A glimpse of "botanicules", after Antonie van Leeuwenhoek's animalcules at the philosophical transactions of the Royal Society in 1677. The fibres were mounted unstained in 99% glycerol (C3H8O3). Being of a different refractive index from plant fibres (Donaldson 2009), glycerol increases the definition of the microscope image. Nail polish is popularly used to seal liquid mounts, but the author abandoned it after initial trials for both practical and aesthetic reasons. It has a ghastly allergy to the glycerol. It will also dissolve in the alcohol used to clean off the immersion oil used with high-powered microscope objectives. The larger coverslip on this trial slide is a No. 1 (thickness 0.13–0.16 mm) made in Japan, the smaller one a No. 0 (0.085–0.13 mm) made in Germany.

Old-school circular coverslips were used in this project, made by the Matsunami Glass company founded in 1844. The box features the layout and typeface quintessential of engineering drawings of the mid-20th century. The coverslips are one step thinner than the required thickness for the objectives used, in order to accommodate additional thickness in the mounting medium. Circular coverslips are a physical manifestation of the circular field of view through the eyepiece that makes microscopic observation so magical. Alas, they have mostly given way to square coverslips which the author supposes are easier to mass-produce and waste less glass.

It was polyurethane wood varnish that eventually won my heart, and not just because it is strong and inert to alcohol. Dark rings focus one's eyes and curiosity onto the specimen on the slide, as seen by the author in the Micrarium at University College London, harking back to the early days of the exploration of the microcosmos.

The author paid a visit to the neighbourhood hardware shop, where the auntie picked out for him a can of polyurethane wood varnish from a dusty shelf. Ironically, polyurethane is inert when fully set, but its synthesis and application involve toxic chemicals and volatile organic compounds. Polyurethane was transferred to the slides with a small paint brush, its bristles held close to but not touching the glass, letting the surface tension of the liquid draw it along the edge of the coverslip. The polyurethane was allowed to cure overnight, followed by a second coat to make sure the seal was leakproof and airtight.

The slides were temporarily marked with 3M Magic Tape, which leaves no residue, while permanent labels were prepared. Annotations were handwritten in waterproof archival ink from a 0.2 mm tip, on labels hand-cut from acid-free laid paper. The labels were affixed with polyvinyl acetate adhesive and allowed 12 hours to cure to maximum strength.

All dressed up for a date with the microscope.

Fibres were examined using Nomarski interference contrast microscopy (Lin 2019c) and identified using the following databases:

American Institute for Conservation
Oriental Papermaking Fibres database, University of Melbourne
Dr. Michael Davidson, Florida State University
Museum of Fine Arts Boston
Canada Conservation Institute

Chalky paper. Dark purple ink particles are visible.

Striated paper.

Rough paper.

Substitute paper.

Under crossed polarizers with a 530 nm retardation plate, most of the softwood fibres appear yellow when oriented NW–SE and blue when NE–SW. This indicates that the cellulose microfibrils, which have a positive sign of elongation (i.e. the slow ray runs parallel to the polymer's longitudinal axis), are oriented in the long direction of the fibres (Gray 2014).

A bast (phloem) fibre extracted from a coconut definitive (Lin 2019c), under a 100× violet-corrected plan-apochromatic oil-immersion objective with Nomarski interference contrast. The fibre has longitudinal defects and characteristic lateral nodes at irregular intervals. Bast fibres come from annual crops grown widely in the tropical to temperate regions (Ansell & Mwaikambo 2009, Jones et al. 2017). The fibres contain more cellulose than wood fibres, and the cellulose tends to be more crystalline (Jones et al. 2017). Crystalline cellulose has highly parallel microfibrils and is birefringent (Donaldson 2009), meaning that its refractive index varies with direction. When the differentially refracted rays get realigned into the same plane of polarization in the second Wollaston prism, Newtonian interference colours are generated.

Common types of bast fibres are hemp from the old ropes and sails of ships, and flax from linen rags (Dagnall 2009). The fibres in the stamp paper are more likely flax than hemp, as the latter is brown and cannot be bleached (Dagnall 2009). Retardation measurement with a Berek compensator (above) gave a birefringence value of 0.06, very close to the recorded value of 0.062 for flax (see Wheeler 2021). The predominance of linen fibres seems to contradict the report (Glazer 2004) that cotton rag was the main constituent of colonial stamp papers. It is not inconceivable that the source of rags varied between linen and cotton depending on availability. I tested five stamps (Lin 2019c).

A softwood ray tracheid (water-conducting vessel) with bordered pits for fluid transfer between neighbouring cells. This is probably from Norway spruce. The plant has strong and flexible fibres that are particularly suitable for printing and writing (Tullis Russell 1950).

A probable softwood fibre extracted from a coconut definitive. It appears flat with some twisting as it has collapsed from its original cylindrical shape. Softwood fibres are generally longer and more flexible than hardwood fibres. Softwood pulp makes the paper denser (Glazer 2004).

Hardwood xylem vessel element from Scandinavian birch (Betula sp.), with characteristic fine oblique pitting (see Parham & Gray 1982, Safdari et al. 2011). Eucalyptus xylem has a similar pattern (see Foelkel 2007) but was not used at the time. This birch vessel was probably a contaminant; only a single instance was observed among fibres extracted from several coconut definitives and hardwoods were not in widespread use then (Robert Hisey pers. comm.). Nomarski interference contrast under 100× violet-corrected plan-apochromatic oil-immersion objective, with scattered particles of magenta pigment.

The author's 3D display at the 36th Asian International Stamp Exhibition in 2019.

I am grateful to Robert Hisey, John Barwis, David Beech, Benedict Sim, Ernest Cheah and Clement Khaw for discussions and technical assistance, and to the Nikon Imaging Centre at the Singapore Bioimaging Consortium for providing state-of-the-art microscopy facilities.


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