Nobody ever said dyeing was easy

As anyone who has ever attempted to buy wallpaper with a loved one will know, colours are notoriously difficult to define. One man’s Burgundy is close enough to another woman’s Maroon for Red to be a dangerously ambiguous catch-all term.

But what if more were at stake when choosing colours than marital happiness. What if the choice of one particular shade of blue over another constituted a religious sin. And – as if that weren’t bad enough – what if nobody had actually set eyes on the colour in question since the days of Ancient Rome.

This chromatic grey area is not a hypothetical situation. The disappearance of the colour t’khelet (pronounced with a properly phlegm-filled ‘kh’, if you please) was a pressing question in Jewish theology for well over a millennium. It took generations of rabbis, dye-makers and chemists to bring the dye back from the dead, and in the process explain just how it was that the Jews first got the blues.


In the Old Testament’s Book of Numbers (chapter 15, verse 38), the Lord tells Moses to instruct the Children of Israel to “make for themselves fringes on the corners of their garments, throughout their generations, and affix a thread of t’khelet on the fringe of each corner.”

These fringes are still worn to this day, either on the corners of prayer vests that religious Jews wear daily, or on the edges of prayer shawls that more secular Jews like myself wear once or twice in a lifetime.

A Jewish prayer shawl with distinctive t'khelet fringes

A Jewish prayer shawl with distinctive t’khelet fringes

Their colour is by now virtually standardised, but this is a fairly recent state of affairs. After the Jews were expelled from the Holy Land under Roman rule, those who fled to Babylon were assumed to have had sporadic access to t’khelet until some point in the 7th Century AD. After that, the only existing description of the colour and its manufacture came from the Talmud, an encyclopaedic codex of the Jewish people’s oral traditions compiled while in exile.

Needless to say, it is pretty goddamned hefty.

The Talmud also gives rather spectacularly vague instructions for the manufacture of t’khelet, which can be summed up as follows.

  1. It is taken from the blood of the hillazon.

Now, you’re going to want to know what sort of well-groomed animal this hillazon must be in order to have blue blood, but let’s stick a pin in that for the moment and move on to the next step of the recipe, which reads:

  1. We mix the blood of the hillazon “together with other ingredients.”

That’s a direct quote. Not even kidding.

Now, the Talmud specifies only three characteristics of the hillazon, namely:

  • It resembles the sea in its colour,
  • In shape it resembles a fish,
  • It appears once in seventy years.

And this was all that scholars had to go on.

Various secular and religious attempts were made to identify the hillazon over the centuries, but the closest anybody came until the modern era was a 19th Century rabbi named Gershon Hanoch Leiner. Sometimes known as the Radzyner Rebbe after the Polish town of Radzyn where he lived and taught, Leiner became obsessed with correctly identifying the hillazon.

As those of you who will have read Michael Chabon’s The Yiddish Policemen’s Union will know, there are certain branches of Judaism which believe the world needs to be properly spruced-up and given a makeover for the eventual return of the Messiah. Some devote their lives to reconstructing models of the Temple in Jerusalem, others to identifying the twelve gemstones in the breastplate of the Great Rabbi (as modelled below by John Cleese). And some, such as the Radzyner Rebbe, believed the long-awaited visitor would not arrive unless his followers were wearing the appropriate shade of blue.

Nobody expects the return of the Messiah

Nobody expects the return of the Messiah

Leiner spent many years studying the question, and after the great aquarium in Naples was opened in 1874, went to consult there with local scholars to identify the correct maritime animal. Leiner was smart enough to realise that ‘blood’ may have been a primitive interpretation of a squid’s ink, and so settled on the common cuttlefish as the source of the elusive dye. He discovered that the ink’s distinctively black colour could be changed to blue if heated in the presence of iron filings, and so excitedly brought his recipe back to Radzyn and set up a factory to produce what he believed was the rediscovered t’khelet.

Production continued at a rapid pace until the factories were destroyed during the Second World War, and most of the Jews who operated them were deported to the extermination camp at Treblinka. Those few who survived the war eventually made their way to Israel, where they were able to painstakingly revive the process and continue manufacture until the present day.

T'khelet thread made using the Radzyn process

T’khelet thread made using the Radzyn process

An old Jewish joke says that for every 2 Jews you get n>2 opinions – although naturally no two Jews can agree as to the exact number that should be in the punchline. Consequently, Leiner’s revolutionary process was bound to leave some sceptics unconvinced.

In 1913, 22 years after Leiner’s death, a young Irish rabbi by the name of Isaac Herzog was completing a PhD at the University of London. As part of his research he decided to subject some of the Radzyn dye to chemical analysis, and sent samples to a number of laboratories across the continent. The results, published in a dissertation entitled Semitic Porphyrology, would catapult him to the front rank of Jewish scholars, and lead to his installation as the Chief Rabbi of Ireland and eventually as first Chief Rabbi of Israel.

Herzog’s chemical analyses yielded a number of interesting results. Rather than being the product of an organic dye, as he would have expected, the Radzyn blue was in fact comprised of an inorganic chemical called ferric ferrocyanide, also known as Prussian Blue. It turned out that when heated in the presence of iron, organic molecules in squid ink break down and their constituent atoms of carbon and nitrogen recombine with iron. Consequently, the nature of the hillazon was irrelevant to the formation of the dye, as any organic chemical would react in the same way. With a bitter, ferrous irony, the hydrogen cyanide gas used in death camps such as Majdanek and the Redzyn t’khelet-makers’ Treblinka would have reacted with the iron contained in the chamber walls in exactly the same way.

Yitzhak Halevi Herzog, first Chief Rabbi both of the Irish Free State and the State of Israel

Yitzhak Halevi Herzog, first Chief Rabbi both of the Irish Free State and the State of Israel

Herzog became increasingly convinced that the true origin of t’khelet was a sea snail known as Murex trunculus, which had been used as a source of dye by other Mediterranean civilisations. The overwhelming archaeological proof that emerged at the time was difficult for him to reconcile with the fact that the Murex had none of the properties attributed to it by the Talmud (ie it was not the colour of the sea, did not resemble a fish and had no known seventy-year cycle).

Herzog’s most fundamental objection, however, was that Murex trunculus could only be made to produce a violet-blue dye, rather than the sky-blue traditionally associated with t’khelet. The two potential hillazons – cuttlefish and sea snail – battled it out on the fringes of Jewish prayer shawls for much of the 20th Century. It was only in the 1980s that an accidental discovery revealed a chemical process Herzog had overlooked, and which finally resolved the historical issue.


Murex trunculus

The dark purple Herzog was familiar with was obtained by smashing a part of the Murex sea snail known as the hypobrachial gland. This is equivalent to the ink sac found in cephalopods such as squids and cuttlefish, but in sea snails contains a clear mucus-like liquid.

This mucus itself contains a molecule known as indole, which occurs naturally in the intestines of most animals. Most digestive processes unite it with sulfur in order to remove it efficiently, but within Murex indole also gets bound to atoms of bromine and potassium. Once exposed to air and sunlight, the bulky molecule reacts with an enzyme known as purpurase to form a chemical known as dibromoindigo, responsible for the dark colour known to the ancient world as Tyrian purple.

If the dibromoindigo is exposed to ultraviolet light, however, which rarely happened in the laboratories Herzog had consulted, then the bromine bonds are broken and the molecule becomes indigo, a chemical capable of dyeing cloth a pure celestial blue.

The validity of this process was eventually confirmed in 2011 when a small sample of blue cloth was found at the ancient Israeli site of Masada. Believed to be over 2000 years old, a study of the material revealed the dye was chemically identical to indigo, confirming the historic connection of t’khelet with Murex trunculus.


Time for one final anecdote.

Herzog’s groundbreaking research just over a century ago has made him one of the most celebrated religious figures of the 20th Century. A fluent Irish speaker and staunch supporter of Irish independence, he was a popular figure in his adopted country. His son would go on to become Israel’s sixth President and first Irish-born head of state, a fact commemorated by a plaque on the wall of his Belfast birthplace.

Some weeks ago, however, during the time of Israel’s Operation Protective Edge in Gaza, the plaque was removed following a series of anti-Semitic acts of vandalism. Graffiti was scrawled on the side of the building and items were thrown at the house, leading the local council to remove the plaque before hooligans could get there first.

The resulting outrage has had the beneficial by-product of introducing more people to the Herzog family’s Irish connection. It has also, if only through the distinctive colour of the plaque, helped underline that there is a single thread that runs continuously through Jewish history, and that it is a distinctive shade of blue.



Gilead Amit is a science writer with a colourful sense of humour. He tweets @gileadamit

This article draws heavily from the following resources:

One thought on “Nobody ever said dyeing was easy

  1. Susan Burns

    What about the fact that the Murex does not look like a fish? Is the Murex the winner of the Tekhelet mystery because of the archeological evidence? I doubt that cuttlefish leave any evidence behind. Their cuttlebones were used as jewelry molds.


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