Everyone knows the story of Tyrian Purple, the dye extracted in the Eastern Mediterranean (and elsewhere) and prized by the Romans for its beautiful magenta hue. Everyone also knows that the production of the dye required about 20 billion shellfish to extract enough purple dye to colour a gnat’s handkerchief. I exaggerate, but it was a lot of effort to go to. 2000 years later, chemist and scholar of artists’ pigments, Arthur Herbert Church, a Professor at the Royal Agricultural College in Cirencester during the mid 19th Century, discovered an even rarer animal pigment which, somewhat surprisingly, some thought may have had potential as an artists’ pigment.
On 4th May 1869, the treasurer of the Royal Society of London, Dr. W. A. Miller, presented a paper on behalf of Professor Church, entitled “Researches on Turacine, an Animal Pigment containing Copper”. The abstract is printed in the Transactions of that year. Church’s research had discovered a ‘remarkable red pigment’ which he called turacine (later referred to as turacin). This pigment had been extracted from the feathers of several species of a tropical African bird, the turaco. More specifically, it was extracted from “about fifteen of the primary and secondary pinion feathers of the birds in question”. It is now known to be a porphyrin.
Turacos are members of the Musophagidae (“banana-eater”) family, they are also known as plantain-eaters and feast on fruit. They are poor flyers but good climbers, with specially adapted claws for clambering about in trees. Many species do have beautiful, red wing feathers, which were much prized as personal ornaments by Zulu aristocracy. Recent work on turaco phylogeny (Veron, 1999) have identified 23 species, and determined that the 17 turacin-bearing species belong to the genus Tauraco, Ruwenzorornis, Gallirex and Musophaga.
Turacos do have remarkable pigmentation. Many of the above species are predominantly green and they are the only birds to have a true green pigment which has been named turacoverdin. The colouration in other green-plumed birds is derived from a combination of yellow pigments (such as carotene) combined with optical blue effects. Turacin and turacoverdin are only encountered in turacos. With (1957) states that the red feathers contain up to 5% turacin and are therefore the richest known natural source of any porphyrin. Torben With’s paper in Nature in 1957 identified turacin as an organo-copper complex, with 6% copper complexed with uroporhyrin III.
The biochemist Claude Rimington (1938) relates that Church’s interest in turacine had been piqued when he had been told that the feathers of a bird owned by a Mr Ward of Wigmore Street had released a red pigment when they were placed in a jar of water, and indeed, this process had been much facilitated when soap (an alkali) had been added. Incidentally, stories of turaco feathers losing their colour in water are probably a stretch of the imagination, the birds’ colour does not wash off in the rain! Furthermore the mystery deepened when a pair of turacos, sent to a friend by a military medical officer, based in the Gambia, Dr. B. Hinde, were released into a well-proportioned aviary. Within days the red colouration in their wing feathers had been lost and the feathers were green, much to the disappointment of the new owner. Church deduced that this colour change was due to the loss of copper and subsequently linked this to a diet available only to birds living in their native, sub-Saharan Africa. He postulated that, back home on the veldt, the birds were ingesting grains of copper minerals. In his experiments leading up to his publication in 1869, Church had successfully extracted turacin from four species of turaco.
Church went on to publish a more detailed description of turacine in 1892. A concern over his understanding of this pigment was the essential occurrence of copper and how the birds had acquired this element. In the second paper he rejected the idea that the copper was derived from the birds eating ‘grains of malachite’ or similar copper minerals, and that the copper could be obtained from fruit digested by the birds. Further to the unfortunate discolouration of the birds sent by Dr Hinde, Church had found out that birds living in captivity and fed on bananas retained the red colouration. As further evidence for a fruit-rich diet imparting copper, he cited the work by Italian chemist, Dr Giunti, that amongst other things, hedgehogs contained 0.016% copper and certain lizards contained over 1%. He also went on to say that he had now managed to extract turacine from all species of the bird. The extraction method is given as follows (Church, 1869):
“The red parts of the vane are first thoroughly washed with distilled water, and then, after drying treated successively with absolute alcohol and with ether. The material is allowed to dry before being extracted … with exceedingly weak, aqueous ammonia. The crimson solution thus obtained is filtered, and then precipitated by pouring it into a large excess of pure strong hydrochloric acid diluted with twice its bulk of water. … Thus in an operation in which about 4 grms of this pigment were dealt with, it was necessary to increase the volume of the mixture of turacin, hydrochloric acid and water to nearly one gallon before its thick consistency could be so reduced as to permit of its being brought upon the filter. Filters of the finest calico were found to be far preferable to those of paper … the method of vacuum filtration was adopted. All the operations should be conducted quickly; exposure of the moist turacin to light should be avoided as far as possible.”
Church does not say how many feathers were used to extract this dye. However in a latter reassessment of the pigment, Claude Rimington (Rimington, 1938) was able to extract between 0.1 – 0.15 g from the red plumage of a single bird. Research into turacin and its derivatives has continued, thanks to Church’s initial findings. As a unique chemical secreted by turacos, turacin’s value is little more than novelty, though work in the first half of the 20th century found it useful in understanding the biosynthesis of porphyrins in general and hoped it could shed light on the causes and treatment of diseases such as porphyria. Nevertheless, Church’s paper of 1892 is very thorough in its analysis and presents, amongst other things excellent absorbance spectra of turacine, which Rimington could not fault.
Claude Rimington (1902-1993), a professor of Chemical Pathology at University College Hospital Medical School, became the leading authority on porphyrins and continued to work on them for the rest of his life. He published further papers on turacin and collaborated with Torben With (see With, 1957). Rimington had worked in South Africa in the 1930s and these experiences sparked his interest in turaco pigmentation and as a consequence, he became aware of the work of Arthur Church. Rimington, along with his colleagues Ida McAlpine and Richard Hunter published the famous paper of 1968, postulating that George III’s erratic behaviour was due to the condition variegate porphyria, a concept much employed in Alan Bennet’s 1991 play ‘The Madness of George III’ (McAlpine et al., 1968). Anyway, I digress.
Arthur Church was deeply interested in artists’ pigments and published a handbook on the chemistry, provenance and manufacture of pigments and other painting materials, ‘The Chemistry of Paints and Pigments’ a book which in its 1901 edition, became a bible to myself and my colleagues whilst we were compiling The Pigment Compendium (Eastaugh et al., 2004 & 2008). To be fair to Church, he never seriously proposed turacine as a potential artists’ pigment. This speculation comes from his contempory, T. W. Salter, who’s book, another painters’ manual ‘Field’s Chromatography; or treatise on colours and pigments as used by artists’ was published in 1869 when Church’s discovery of turacine was hot off the press. Perhaps Salter had even been at the Royal Society on the day in May that year when Church’s paper was read.
Salter (1869) writes ‘An interesting account has lately been given by Professor Church of a new animal pigment containing copper, found in the feathers of … species of turacus, natives of the Gold Coast, The Cape and Natal. Turacine, the name proposed for it, is noticed here only because it is the first animal or vegetable pigment with copper as an essential element … As the entire plumage of a bird yields not more than three grains of pigment, turacine may be looked upon as a mere curiosity’.
Not unsurprisingly, in a later, ‘modernized’ edition of Field’s Chromatography (Scott-Taylor, 1885), the section on turacine has been omitted. Nevertheless, because of its bizarre derivation we decided to include it in the Pigment Compendium despite the complete lack of evidence supporting its use by any artist (it’s up there with Wongshy Red, another dubious pigment described by Salter). To my knowledge turacin has not been synthesised and indeed Church’s own experiments showed it to be fugitive and susceptible to colour changes (Church 1892). As such it would have been a poor and expensive choice as an artists’ pigment, albeit with an exotic caché. However it does occur to me that Church may well have experimented with it, to see how it painted up. Why wouldn’t he?
Church’s 1869 paper is excellent for its time, though he finishes on an undeservingly self-deprecatory note: “… some excuse may perhaps be allowed for my failure to accomplish more towards the elucidation of a colouring matter so anomalous and costly as turacin.”
Arthur Herbert Church was born in London on 2nd June 1834. He was educated at King’s College London and Lincoln College Oxford, going on to a renowned career as a material scientist with a great interest in the decorative arts. His interests were broad, and he published on porcelain (of which he was a collector), food grains (he worked at the Royal Agricultural College in Cirencester) and minerals, and had been president of the Mineralogical Society. Church had discovered in Cornwall the cerium phosphate mineral churchite. An early exponent of archaeological science, he was honorary curator at the Cirencester Museum of Roman Antiquities. He later lectured at the Royal Academy of Arts. His interest in the chemistry and characterisation of pigments came to fruition in his books, ‘The Chemistry of Paints and Painting’, first published in 1890 and running to four editions. Church was an accomplished amateur landscape painter, and had exhibited in the Royal Academy Summer Exhibition of 1854 and struck friendships with the artists of the day, including Frederic, Lord Leighton to whom he dedicates the painting manual. He also published a book on colour theory in 1907. Importantly, from 1894 Church was responsible for the restoration of the frescoes in the Palace of Westminster, developing analytical and practical methods that were an enormous contribution to art conservation and restoration at that time (Kurzer, 2006). Church was knighted in 1909. He died, aged 81, in Kew on 31st May, 1915.
Whilst we were writing the Pigment Compendium, my colleagues and I often wondered where we would be without A. H. Church and his meticulous research into pigments commonplace and arcane.
So, does anyone have any turaco feathers?
References and further reading
Church, A. H., 1869, Researches on Turacine, an Animal Pigment Containing Copper., Proceedings of the Royal Society of London (1854-1905)., 17, 436–436.
Church, A. H., 1892, Researches on Turacin, an Animal Pigment Containing Copper. II., Philosophical Transactions of the Royal Society of London. A (1887-1895). 183, 511–530.
Church, A. H., 1890, The chemistry of paints and painting., Seeley & Co. Ltd., London, 310 pp.
Eastaugh, N., Walsh, V., Chaplin, T., Siddall, R., 2008, Pigment Compendium: A Dictionary and Optical Microscopy of Historic Pigments. London: Butterworth-Heinemann. 960pp.
Eastaugh, N., Walsh, V., Chaplin, T., Siddall, R., 2004, The Pigment Compendium: A Dictionary of Historical Pigments. Elsevier – Butterworth Heinemen. 499pp.
Kurzer, F., 2006, Arthur Herbert Church FRS and the Palace of Westminster frescoes., Notes & Records of the Royal Society., 60. 139-159.
McAlpine, I., Hunter, R. & Rimington, C., 1968, Porphyria In The Royal Houses Of Stuart, Hanover, and Prussia: A Follow-Up Study Of George III’S illness., British Medical Journal, 1, 5583, 7-18.
Rimington, C., 1939, A Reinvestigation of Turacin, the Copper Porphyrin Pigment of Certain Birds Belonging to the Musophagidae., Proceedings of the Royal Society of London. Series B, Biological sciences., 127, 846, 106-120.
Riley, P., 1993, Obituary: Professor Claude Rimmington, The Independent, Friday, 13th Sugust, 1993: http://www.independent.co.uk/news/people/obituary-professor-claude-rimington-1460840.html
Salter, T. W., 1869, Field’s Chromatography; or treatise on colours and pigments as used by artists., Winsor & Newton, London.
Scott-Taylor, J., 1885, Field’s Chromatography; or treatise on colours and pigments as used by artists., Winsor & Newton, London., 207 pp.
Veron, G., 1999, Phylogenie des touracos (Aves, Musophagidae). Analyse des caracteres morphologiques., Journal of zoological systematics and evolutionary research., 37(1), 39-48.
With, T. K., 1957, Uroporphyrin from Turacin: a Simplified Method., Nature, 179(4564), 824.
There are some more good pictures of turacos and their plumage on these websites …
A. H. Church: Wikipedia: http://en.wikipedia.org/wiki/Arthur_Herbert_Church
©Ruth Siddall 2015