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Imperial Purple and Holy Blue - Mollusk Dyes

Dyeing fibres with the use of sea snails (Murex) is an art found in history from the Irish coast lines to the Adriatic seas and the Mediterranean coasts. In Mexico and Guatemala the knowledge is still alive, but this platform is too small to cover them all so I will limit myself to things close to home; the coasts of ancient Israel. (For those who want to read more I highly recommend the book or Baruch Sterman and the website Ptil Tekhelet. )


In the old books the names argaman and tekhelet go hand in hand.

Argaman being a from Akkadian𒅈𒂵𒌋𒌋𒉡 argamannu, meaning “red-purple”. We call this also Tyrian or Royal Purple.

Tekhelet (pronounced with the 'kh' sounding like the 'ch in Bach) was a shade the sages argued a lot about. In the Greek translation of the Septagint it was translated as hyakinthos (ὑακίνθος, "hyacinth", that would make it a violet blue, today the experts say it must have been a sky blue. On the other hand, the samples as I have seen them dyed today are more like a middle blue.

Fabric treated with actual murex dye (photo credit: Clara Amit, courtesy of the Israel Antiquities Authority)

Naama Sukenik of Israel’s Antiquities Authority discovered that a piece of woven wool (found the in Wadi Muraba’at caves south of Qumran in the 1950s) was colored with a dye from the Murex trunculus.

Fragment of the rare purple fabric from 1,000 BCE excavated in the Timna Valley. (Dafna Gazit, Israel Antiquities Authority)

This rare example of Royal Purple was found in the Israeli Timna region, close to the Red Sea in the South. Israeli researchers dated them to circa 1,000 BCE — the era of King David. The earliest ever such finds in this region.


Whatever shade we want to call these dyes today, they both came from sea snails and it must have been a massive operation to create them. Heaps and heaps of murex sea snail shells along the mediterranean coast, either cut with special knives or busted with rocks on stone plateaus to extract the special gland on the inside that hides the mucus that was worth its' weight tree times in gold. The smell would have been absolutely repulsive with the rotting flesh of millions of dead snails: for one gram of dye you need 10.000 snails!

murex trunculus shell on purple dye samples
Murex Trunculus shell, gifted to me by Baruch Sterman

Different species of the predatory Murex snails make different shades of dyes, the ones found most in archeological digs all along the cost of today's Northern Israel and up to Syria, is Murex Trunculus, with Murex Brandaris a respectful second place. If you ever fancy foraging some Murex trunculus yourself this is what you should look out for;

A sea snail with a shell of 4 to 10 cm long. It has a rather high spire with seven angulated whorls, and the shell looks a bit like a fish.

The shell is variable in sculpture and coloring with dark stripes you can see on the inside. The ribs sometimes develop thickenings or spines and give the shell a rough appearance. In the sea bed it is often covered in algae, so it is very hard to actually spot them.

The amount of snails needed, and the manpower required made it understandably the most expensive dye on earth. Per imperial decree, in 301 CE, one pound of murex dye would have cost 150,000 denarii which equaled around three pounds of gold.

The exorbitant price tag of murex dye made it a dye for the lucky elite, who tried to keep exclusive rights to wearing Royal Purple. The Sumptuariae Leges of ancient Rome prevented the use of expensive Tyrian purple dye for ordinary citizens. Only the Roman Emperor could wear a Tyrian purple cape trimmed in golden thread, and Roman senators were the only ones who could wear a Tyrian purple stripe on their toga.

'Fun' fact: According to the Roman historian Suetonius, King Ptolemy of Mauretania’s cloaked himself in purple on a visit to the Caligula. The emperor took this as a sign Ptolemy was doing a bid for the imperial seat and had his guest killed...

On the other side of these Purple seeking elites, the ancient Israelites had clear commandments to create Argaman and Tekhelet dyed wools and linens. For the tabernacle, the priestly garments and last but not least, the one string of Tekhelet dyed wool in a set of tsitsit on the corners of any four cornered garment and the traditional prayer shawl called a Tallit, still worn by observant Jews today.

ritual tassels on a tsitsit, four cornered garment
Tsitsit on the corners of a four cornered garment, with a strand of tekhelet.

As it is written; “Hashem spoke to Moshe saying: Speak to the Children of Israel and say to them that they shall make themselves tsitsit on the corners of their garments throughout their generations. And they shall place upon the tsitsit of each corner a thread of tekhelet… And you shall see it and remember all of the commandments of Hashem and you shall do them,” (Bemidbar (Numbers) 15:37-39).

If we were commanded to have sky blue, then why not just use indigo, or woad? From the Jewish commentary called the Talmud, we then understand this tekhelet came from a chillazon, which also today means 'snail' in Hebrew. This place will not be the platform to discuss all the minute details, but you will have to take my word for it, that using regular plant based indigo, was not only considered wrong, it was a major transgression.

If both argaman purple and tekhelet blue come from the same sea snail, how was this difference achieved and how does it work, scientifically? It seemed technically impossible, and the original ins and outs of snail dyeing (in both shades) had gotten lost over the centuries. What do we know? Vitruvius mentions the production of Tyrian purple from shellfish. Aristotle described the shellfish from which Tyrian purple was obtained and the process of extracting the gland that produced the dye. Pliny the Elder described the production of Tyrian purple in his Natural History:

After it (the shellfish) is taken, the vein [i.e. hypobranchial gland] is extracted, which we have previously spoken of, to which it is requisite to add salt, a sextarius about to every hundred pounds of juice. It is sufficient to leave them to steep for a period of three days, and no more, for the fresher they are, the greater virtue there is in the liquor.
It is then set to boil in vessels of tin [or lead], and every hundred amphoræ ought to be boiled down to five hundred pounds of dye, by the application of a moderate heat; for which purpose the vessel is placed at the end of a long funnel, which communicates with the furnace; while thus boiling, the liquor is skimmed from time to time, and with it the flesh, which necessarily adheres to the veins.
About the tenth day, generally, the whole contents of the cauldron are in a liquefied state, upon which a fleece, from which the grease has been cleansed, is plunged into it by way of making trial; but until such time as the colour is found to satisfy the wishes of those preparing it, the liquor is still kept on the boil. The tint that inclines to red is looked upon as inferior to that which is of a blackish hue. The wool is left to lie in soak for five hours, and then, after carding it, it is thrown in again, until it has fully imbibed the colour.

Just adding salt to fish and having it ferment for 10 days, would not bring the ph in the vat to the alkalinity needed to get the prize ingredient dibromoindigo into solution, there are ingredients missing here. And if this recipe is for Tyrian purple, how did the Israelites achieve sky blues?

Another description (not mentioned often enough!), but of a direct dye process, comes from Edward Bancrofts' Experimental Researches Concerning the Philosophy of Permanent Colours. Page 80 and onwards.

The year is is 1683, and this takes place in Ireland. According to Edward Bancroft, Mr. William Cole of Bristol heard about a person living at a sea port in Ireland who made a considerable gain by marking fine linen with a delicate durable crimson. -so far so good- Then he continues to explain how to express the 'white liquor in the vein' from the poor snail and here it comes;

"Letters or marks made in this way, with the white liquor in question, will presently appear of a pleasant green colour, and if placed in the sun, will change into the following colours, i.e. if in the winter, about noon, if in the summer, an hour or two after sun-rising, and so much before setting (for in the heat of the day in summer the colours will come on so fast, that the succession of each colour will scarce be distinguishable: next to the first light green, will appear a deep green, and in a few minutes this will change into a full sea green: after which, in a few minutes more, it will alter into a watchet blue: from that, in a little time more, it will be of a purplish red: after which, lying an hour or two (supposing the sun still shining), it will be of a very deep purple red: beyond which the sun can do no more."

Still no permanent blue...not in vat dyeing and not in direct application of the dye from mollusk to fiber.

Scientists, scholars and chemists tried to understand and eventually dismissed the possibility altogether. Until in the 1980s, Otto Elsner, a chemist from Shenkar College in Israel, by chance discovered that when he put his smelly snail experiment in the open window, the sun exposed vat gave a consistent blue instead of purple.

You see, the main 'ingredient' of Tyrian purple is dibromoindigo, aka 6,6'-dibromoindigo, molecular Formula C16H8Br2N2O. It is similar to the build of the indigotin molecule, just with 'Br' added left and right.

In a reduced vat his connection a bit weak, so that under the influence of UV rays, the 'dibromo' part gets disconnected and what stays is the 'indigo' and we all know how that indigo behaves in a vat (and if you do not, I refer you back to this blog).

Always a fan of a good experiment I managed to get my hands on some dried Murex glands used to dye the tsitsit strands today in Israel, when working together with the Ptil Tekhelet Foundation, so I could reproduce a vat and try first hand to create both blue and purple.

The glands smell.... fishy and a bit like sea weed and I was not about to use original methods using fermentation, instead I opted for a mini 1 litre Sodium Hydrosulfide vat.

The basic recipe

1 litre water (40ºC);

5 grams dried murex glands, dried and ground into a paste.

12 grams soda ash

5 grams sodium hydrosulfide (and in hindsight, you can probably use less)

The first vat was made in full TL light and the reduction process looked like this:

Results for dyeing with this vat on silk and wool:

wool and silk dyed with Murex Trunculus after UV exposure of the vat
Tekhelet dye samples

Keeping in mind that this vat had merely been exposed to the artificial (horrible) lighting in the studio, I opted to do the second experiment for purple with the beaker in a cardboard box so it could remain in relative darkness. I only took the box off for the purpose of taking pictures of the process. Dyeing took place in the studio corridor, in the dark.

Results on wool:

I found that silk dyeing in this second vat still turned blue on me, so that would mean that the silk has a bigger affinity for the indigotin, and wool a bigger affinity for dibromoinidigo. Also; your fibers need much longer in the murex vat than they would need in a regular indigo vat. After previous experiments I already discovered that 20 minutes is the minimum to get any decent shade...


Back to history; around the 12th century the disappearance of sea snail dyeing was caused by a natural decline in the availability of Murex mollusks, which is a beautiful way to say they were over-harvested to almost the point of extinction. Another factor; the region of the ancient Israel coastline was famously politically unstable and war infested (read Jerusalem, The Biography by Simon Sebag Montefiori for an excellent read) and after the fall of Constantinople the local dye industry pretty much disappeared. Third reason may very well have been a change in fashion, and the Christian church switching from Tyrian Purple to Kermes dye for ritual garb.

Today, murex sea snails are considered a sea food delicacy and the dyeing takes place in very very few places. In Oaxaca Mexico and Guatemala some direct dyeing still exists and in Tunisia Mohammed Ghassen Nouira runs a project reconstructing the old ways of Tyrian Purple. In Israel, the only place currently dying real Tekhelet blue, is 'Ptil Tekhelet'.

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