The Guardian: Monday 5th December 2016.

‘The shellfish that was one of the main sources of Tyrian purple – one of the most storied and valuable trading products in the ancient world – has disappeared from the eastern Mediterranean coast, amid warnings of an ongoing multi-species collapse blamed on global rises in sea temperatures.’

Historical cessation of shellfish dyeing The word ‘Tyrian’ derives from the city of Tyre on the north African coast, an area long associated with the Phoenicians and the shellfish dyeing industry. Tyrian Purple has already ‘disappeared’ once. Although an article linked from the Guardian states ‘snail-fueled purple persisted until chemists learned to make synthetic dyes,’ this is quite untrue.

It’s well known (in the dye world, at least) that shellfish dyeing largely ceased around the time of the Fall of Constantinople in 1453, after which the last dyers seemed to have disappeared. And in the eastern Mediterranean, purple dyeing ceased almost a millennium earlier as a result of the Arab conquest at the beginning of the 7th century.  Analysis of historic textiles continues to confirm this. The biochemical method of shellfish dyeing was complex, relying on processes which were not understood chemically, and were probably only passed down within families. Basically, when the dyers ‘disappeared’ they took the method with them. Any contemporaneous written records of the dye process are incomplete or ambiguous, and cannot be used to make a vat.

Recovery of the dyeing method Shellfish pigment must first be made soluble, (as with any dye), and this only occurs in alkaline conditions of around pH 8 and higher. An additional requirement for dissolution of the pigment is that it must undergo ‘reduction’. In reduction the pigment’s molecules are converted to a slightly altered, but more soluble, molecular structure. This reduction process is achieved by removing oxygen from the pigment molecules, or by adding hydrogen to them.  The vat turns a yellowy colour and fibre, threads or fabric are introduced. Colour will return to dyed items as they re-oxygenate on removal into the air. Readers who are indigo dyers will be familiar with this process.

The lost dyeing method Until the painstaking work in the 1990s of a retired engineer, the late John Edmonds, the exact method for creating a true shellfish purple reduction vat was lost. (Note that a reduction vat is entirely different from a direct application process performed by smearing the pre-pigment secretions).  Edmonds used his knowledge of woad fermentation to recreate the ancient shellfish dye method. He knew, from the early 20th century work of Paul Friedländer, that shellfish dye was an indigoid and would need a reduction process to work.  Edmonds used shellfish pigment extract for colour, and the rotting flesh of tinned cockles to start the required fermentation.  In subsequent years, chemist Zvi Koren (more about Zvi later) and artist Inge Boesken-Kanold separately explored and perfected more authentic historical procedures for dyeing and painting using shellfish purple.

The purple threads The earliest known historically accurate shellfish dyeings since the 15th century were, until recently, the initial samples produced by Edmonds. But in 2008 I discovered a small envelope containing purple cotton threads in a nineteenth / early twentieth century archive. They were labelled in as having been dyed with ‘the bodies of shellfish’. Could they be genuine?

Zvi Koren In 2011 I wandered around an exhibition in the company of Zvi Koren. Zvi is an internationally known and respected authority on shellfish purple and his lively presentations on the subject make him a unique and entertaining conference speaker. He showed interest in my presentations on orchil research, and we discovered a mutual obsession for appallingly groanworthy puns.

I tentatively mentioned the envelope of shellfish dyed threads I had found.  Zvi was clearly sceptical, as rightly befitted an analytical chemist, and was fairly certain the threads would be fake. He told me that only a scientific analysis, rather than visual inspection, would prove or disprove the claim. In his work, Zvi has analysed archaeological dyeings previously claimed by analysts to be shellfish dyed. Zvi’s precise analyses on these same artefacts showed that the ‘real purple’ was in fact an overdye produced from madder and indigo. He reminded me that prior to the work of Edmonds and others I’d have to go back nearly 600 years to find a true dyeing supported by chemical analysis. Paul Friedländer, who first identified the chemistry of shellfish purple in 1909, left no known samples.  But Zvi’s a good sport and was clearly intrigued. He suggested I send a small sample of the threads to him for analysis at the Edelstein Center for the Analysis of Ancient Artifacts, in Israel. So I did.

The research Zvi has described his astonishment when his analysis found the dyeing to be genuine shellfish purple, and he suggested we write a paper together. The work we undertook mapped a possible scenario for how the dyeing came about, why, and at what date. It involved parallel investigations based on Zvi’s scientific analysis of the threads through photomicrographic images and instrumental chromatography. We also studied classical and biblical texts; 19th century literature; the history of science and scientific connections; and the remarkable Bedford family of Leeds.  Zvi was extremely patient with my lack of chemical knowledge and I continue to be grateful for his clear explanations, and the general good humour which illuminated the science I frequently failed to grasp.

Significance of our research So is this a big deal? We definitely think so. It’s huge!  Firstly, before the Tyrian Purple dyed threads I found, no other dyeings have been confirmed since around the 15th century. That’s of considerable interest to researchers. Additionally, their very existence superbly illustrates the activities, interests and connections of an industrious Leeds family in the late 19th and early 20th century. More of that in Part Two – which will follow in the next fortnight.

If you are interested in knowing more about any aspect of this research please contact me through the blog. 

Thanks Many thanks to colleague and friend Zvi Koren for his knowledge, diligence and support, and for his comments and additions to this and the following blog. And not forgetting the puns.

Links and bibliography

Whitworth and Koren paper published in Ambix. Available from Taylor & Francis Online here.

Ancient shellfish used for purple dye vanishes from eastern Med  Guardian article , December 5th 2016

Related posts  on this blog

Testing Times 1 & 2

Getting to Blue

A Purple Pursuit

French Connections

Reasons to be Stressful

Talking Orchil

Dyes, History, and a Chilly Trip to Yorkshire

Inge Boesken Kanold artist researching and working with shellfish pigment

The Edelstein Center for the Analysis of Ancient Artifacts

John Edmonds’ book: Tyrian or Imperial Purple Dye: The Mystery of Imperial Purple Dye, Historic Dye series no. 7, Little Chalfont, 2000. Published by the author.

Smearing process of dyeing