©Lin Yangchen

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There were at least nine printings of the bma malaya 15 cents in different shades of ultramarine and blue on three types of paper, as first documented by Cameron (1950). These have spawned much confusion, with major catalogues disagreeing with one another. Dr Abdul Majid Dato Kassim leaves them all in the dust with no fewer than 32 combinations of shades and papers, qualifying the colours with the descriptors “pale", “light", “bright", “deep", “dull" and combinations of these.

Stamp shades are in fact an infinite continuum.

Even a single printing run can use different batches of ink, and even a single batch of ink can fluctuate with temperature, mixing, and printing pressure (Fernbank 2013). Subtle shade differences were sometimes caused by accumulation of ink on the rollers that inked the plates. In an 1898 letter (Easton 1958), De La Rue explained: We beg to say that in printing it is impossible to avoid a certain number of sheets being either of too light or too dark a shade. The light sheets are printed immediately after washing up, and the dark sheets occur when the process of printing goes on for too long a period without washing up the rollers.

On top of that, shade is also affected by the paper (White 1979) and by chemical changes in the ink induced by light, heat, moisture and other agents. Even opening an album or scanning a stamp has noticeable cumulative effects over time (Ian Greig comm. 2020).

Hofmeyr (2020) proposed a methodological standard for quantifying key shades based on CIE Lab coordinates obtained through spectrophotometry, but even that can be frustrated by the confounding factors listed above.

The pre-war ultramarine on rough paper, locally overprinted post-war in black (Cameron 1950, Barker 1993) and issued in November 1945.

Raman spectroscopy of the ink on another 15 cents of the same pre-war vintage, showing a good match with the three largest peaks in a reference spectrum (Caggiani et al. 2016) of ultramarine, a sulphurous sodium aluminosilicate. To aid comparison, the empirical spectrum (download data) was baseline-corrected with a third-degree polynomial using the ModPoly algorithm (Lieber & Mahadevan-Jansen 2003) in the R language for statistical computing, and each spectrum was normalized to Raman intensity within (0,1). The vertical jump in the ultramarine reference spectrum at 1700 cm−1 is an artifact caused by the combined plotting of separate spectra; Raman intensities of this spectrum below and above 1700 cm−1 should not be directly compared. The two large empirical peaks around 1350 cm−1 and 1600 cm−1 appear to coincide with those of ultramarine, but they are slightly out of alignment and too high to be explained by ultramarine alone. Furthermore, the peak at around 1600 cm−1 may actually be two separate peaks. These large peaks could be signals from something else. Carbon has peaks that come close to matching but they don’t align properly. The smaller peak in the carbon reference spectrum has broad shoulders not seen in the corresponding peak in the empirical spectrum. Additional peaks from unknown substances occur around 900 cm−1 and 1175 cm−1.

The elusive pale cobalt blue (Malaya Study Group 1993, Cockburn 2015), shown here unoverprinted. Many philatelists regard this as no more than a fading of the normal 15c. Faded ink, however, is usually accompanied by other signs like oxidation or degradation of the paper. In this example and another in the possession of the author, the paper looks relatively fresh and the watermark is clearly discernible on the reverse.

The dull ultramarine on substitute paper is an oddity with a pronounced reddish cast to the naked eye. The blotchy impression on the right may be a 'dry print' caused by low temperature or bad mixing of the ink, and/or some physicochemical repulsion between the ink and the coating on the substitute paper.

Photomicrograph with a 20× plan apochromatic objective and transmitted Köhler illumination. The paper looks yellow because of a hinge on the reverse, but the shade of the pigment in the micrograph is relatively unaffected. Compared with the ultramarine, the dull ultramarine has more red and green pigment particles. This probably contributes to its distinctive reddish cast.

In fact, the laser-induced ultraviolet fluorescence spectrum of this shade under 325 nm excitation has a peak at about 590 nm which is not found in any of the other 15 cents shades (Lin & Magis 2018). The peak corresponds closely to that in the spectrum (not shown) of a Selangor 10 cents. As a magenta ink very similar to that on the Selangor stamp was used for some of the BMA 10 cents, the ink for the 15 cents could have been inadvertently tainted by residue from an earlier batch of magenta ink mixed in the same vessel. I doubt this was intentional.

Bright ultramarine on substitute paper, with what appears to be a sulphuretted overprint.

Photomicrograph with a 20× plan apochromatic objective and transmitted Köhler illumination. The ultramarine pigment appears to be of the synthetic form, with more rounded particles than the natural form. The synthetic form is also characterized by small particle size with occasional large granules formed by aggregation (Plesters 1986).

Deep ultramarine on substitute paper (Lin & Magis 2018).

The fabled Steel Blue on substitute paper. The blues lack the reddish cast of the ultramarines.

Photomicrograph with a 20× plan apochromatic objective and transmitted Köhler illumination. Steel blue might have different ink additives than the other blues, or simply be a different stoichiometry of ultramarine. Ultramarine pigment takes on different shades depending on its exact molecular structure which varies in the proportions of sodium and sulphur on the underlying aluminosilicate skeleton (Plesters 1986).

Blue on chalky paper. Printed from Plate 2, which has the 'MALAYA' at the top engraved more closely than usual to the top of the frame (author's observation). The stamp on the right has probably experienced significant environmental exposure. Astonishingly, these two look more different from each other than some of the other printings do from one another, yet both have the essential tonal characteristics that identify them as blue on chalky. This pair of changelings demonstrates the variability that can occur across stamps of the same printing.

A rare self-made postcard with a view of Singapore's General Post Office from Clifford Pier, affixed with blues on chalky paper with blue handwriting. The G.P.O. was not only the bastion of the coconut definitives, but also the point from which all road distances in Singapore were measured. In the background on the right is the Post Office Pier along Collyer Quay, linked to the G.P.O. by a tunnel 35 metres long. Mail arrived from Britain by sea every Friday (Bala Subramanion comm.).

Ultramarines on chalky paper have a distinctive "milky" consistency not seen on rough and substitute papers.

The 12¢ and post-war 20¢ blue on chalky paper have the same "milky" consistency.

Selected shades differ in their laser-induced ultraviolet fluorescence spectra (download raw data). But remarkably, they all have peaks or shoulders at the same wavelengths: 500, 520, 690, 900 and 970 nm. It's the peak ratios that differ from stamp to stamp. This suggests that the inks comprise varying compositions of a similar set of pigments, or varying concentrations of a single pigment mixed with other substances, rather than a different pigment for each stamp (Lin & Magis 2018).

Energy-dispersive X-ray spectroscopy of pre-war, BMA and post-war blue coconut definitives (Lin 2020d) suggests that they were all printed with ultramarine pigment (download raw data). Iron and nitrogen were not detected, suggesting that Prussian blue is absent. Why didn't they use Prussian blue, which was also cheaply available? Prussian blue is a very intense pigment that has to be diluted considerably. This may have made it difficult to mix a consistent shade. After dilution the pigment also becomes prone to discolouration by ultraviolet exposure. Incidentally, De La Rue was plagued by fading blues before the war (Len Stanway comm.). Ultramarine might have been considered more lightfast; it can last 500 years without fading (Plesters 1986). There might have been additional logistical, political, historical or chemical reasons.

Ultramarine was originally made from lapis lazuli. Most of the world's supply of the natural ore has been mined from a remote valley in Afghanistan for more than 6000 years. It cost more than gold; Renaissance painters reserved it for the robes of the Virgin Mary, and King Tutankhamun used it as eyeliner (on his gold mask). A cheap synthetic alternative was finally invented during the Industrial Revolution.

In 1962, French artist Yves Klein invented a shade he called International Klein Blue, which uses a large amount of ultramarine. I saw the original work at the Tate Modern in London. In Klein’s words, “Blue has no dimensions, it is beyond dimensions”.

I am grateful to Richard Hale and Axel Magis for making their material available for study and for comments that improved the article. Thanks also go to Lim Kim Yong and Sow Chorng Haur at the Department of Physics, National University of Singapore, and Wulf Hofbauer and Li Zhen at Science Centre Singapore.


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