Fibre analysis - Lin Yangchen
©Lin Yangchen


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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).

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 oriented microfibrils and is birefringent (Donaldson 2009), meaning that its refractive index varies with direction. This causes optical interference which produces the Newtonian interference colours in the Nomarski image. 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). 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 pulp made the paper more dense (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.

Separated fibres of chalky paper under Nomarski interference contrast microscopy (Lin 2019c). Dark purple ink particles are visible. See how the fibres were extracted.


Separated fibres of striated paper under Nomarski interference contrast microscopy.


Separated fibres of rough paper under Nomarski interference contrast microscopy.


Separated fibres of substitute paper under Nomarski interference contrast microscopy.

Acknowledgements
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.

References


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