Murex Tekhelet: A Proposal for an Alternative Source of Biblical Blue
- Suzanne Dekel
- Jul 7
- 7 min read
For centuries, the precise nature of the Biblical tekhelet, the sacred blue mentioned in the Torah, remained an enigma. In the Book of Numbers (15:38), we read: "Speak to the people of Israel, and tell them to make tassels on the corners of their garments throughout their generations and to put a cord of blue [tekhelet] on the fringe at each corner."
But what was tekhelet, and how was it made?
The Mystery of the Sea-Creature Dye
Ancient Jewish texts, including the Talmud (Menachot 42b), tell us that tekhelet came from a sea creature called the ḥilazon. The Jewish tradition of producing the prized blue was interrupted, especially after the loss of access to the Mediterranean and the disruptions following the Roman destruction of the Temple, and over time, the identity of the ḥilazon and the method of extracting its blue dye were lost. By the Middle Ages, rabbis such as Maimonides acknowledged that the knowledge of tekhelet had disappeared.
It wasn’t until the 20th century that serious efforts were made to rediscover the process. The primary clue is to be found in the ancient dyeing practices of the Phoenicians, who were famous for using sea snails, particularly Hexaplex trunculus, Bolinus brandaris, and Stramonita haemastoma, to produce Tyrian purple, one of the most prized dyes of antiquity.
Ancient Dyeing on Israel’s Coast: Which Mollusk is Behind Biblical Blue and Purple
When we look along the shores of ancient Israel, from the rocky inlets of Akko in the north to the sands of Ashkelon in the south, we find compelling evidence of this once-thriving industry rooted in deep, royal color.
Hexaplex trunculus, formerly classified as Murex trunculus, is native to the Mediterranean and is the species most commonly found in archaeological dyeing sites across Israel’s coastline. Hexaplex trunculus was one of the key mollusks used to produce these sacred dyes. It appears in overwhelming quantities in ancient middens (refuse heaps left behind by dyers), often with a tell-tale hole punctured through the shell exactly where the hypobranchial gland is located. This small gland is where the precious dye precursor was extracted.
Coastal Dye Centers: Industrial Hubs of Ancient Color
One of the most important dye production centers along Israel’s coast is Tel Shikmona, near modern-day Haifa. Excavations there revealed crushed murex shells in enormous quantities, along with dye vats, drainage channels, and stone basins used in the dyeing process. Chemical analysis confirmed the presence of 6,6’-dibromoindigo, the molecule that gives Tyrian purple its hue.
Another key site is Tel Dor, a major port city further south. Here, too, archaeologists found workshops and shell mounds, evidence of a local dye industry operating on a large scale.
Similar finds have been recorded in Achziv and Akko, both linked to Phoenician maritime trade and dye production. The patterns are clear: this was not a cottage industry. This was organized, laborious, and embedded in both the economy and culture.
Even Ashkelon, which is better known for later-period remains, has revealed traces of mollusk processing and evidence of Phoenician commercial activity, pointing to its possible role in the dye trade network. And at Tell Keisan, although inland, archaeologists discovered imported dyed textiles and marine shell remains, suggesting that dyed cloth and raw materials were traded widely beyond the immediate coastal zones.
What's in a name?
The name Hexaplex trunculus comes from Latin and Greek roots, structured in binomial nomenclature used in biological taxonomy.
Hexaplex: from Greek hexa- (ἕξ) meaning "six" and -plex from Latin plectere, meaning "to fold" or "twist." It means the six whorls of the snail’s shell spines.
Trunculus: from Latin truncus, which means "cut off," "maimed," or "truncated." In zoological naming, trunculus often refers to a shortened or stubby form, a reference to the somewhat blunt or truncated appearance of the shell’s spire in comparison to other murex species.
So, Hexaplex trunculus can be loosely translated as: “Six-fold twisted (or ridged) snail with a stubby form.”
The Paradox: One Snail, Two Colors
The question that has puzzled us was: how could tekhelet, a deep sky blue, and argaman (Tyrian purple), a reddish-purple, both come from the same mollusk?
The answer came in the 1980s and 1990s, through the research of Israeli chemist Prof. Zvi C. Koren, and earlier experimentation by Otto Elsner. They discovered that the dye precursor in Hexaplex trunculus contains two color-producing elements: indigoid compounds (blue) and bromine (red), If both are present during the dye process, a purple is obtained. If only the blue compound is available, we will get, well...blue.
Koren's pivotal 1993 discovery demonstrated that if the reduced dye bath (leuco form) was exposed to sunlight during the dyeing process, the bromine would degrade, and what was left was a stable indigo compound, the same structure as that found in woad (Isatis tinctoria) or true indigo (Indigofera tinctoria). Without exposure to light or with heat and oxidation, the brominated purple (6,6’-dibromoindigo) would prevail.
In other words:
Purple = no sunlight, bromine preserved
Blue = sunlight, bromine breaks down
This biochemical sensitivity explains how the same mollusk could produce two distinct hues of argaman and tekhelet, with technique, rather than species, being the differentiating factor.
The Contemporary Tekhelet Revival
Today, several organizations (notably Ptil Tekhelet in Israel) produce tekhelet for religious use, particularly for tzitzit. Their method, modeled on Koren's findings, involves exposing the dye bath to UV light, allowing the blue to develop. This blue is chemically identical to indigo (C₁₆H₁₀N₂O₂), but derives its sanctity from its marine origin.
However, this raises a crucial question: Would ancient dyers have sacrificed costly purple dye to produce a blue indistinguishable from indigo or woad? I say: absolutely not.
The Cost of Color: Time, Labor, and Thousands of Mollusks
Producing even a small amount of dye from Hexaplex trunculus required labor and resources.
Historical estimates suggest that it took approximately 12,000 mollusks to produce just 1.4 grams of pure dye, barely enough to color the trim of a single garment. Pliny the Elder, writing in the 1st century CE (Natural History 9.62), remarked that Tyrian purple was worth its weight in silver due to its laborious extraction and prestige.
Each mollusc yields only a drop of the precious mucous secretion, which has to be extracted from the hypobranchial gland, an internal organ buried deep within the shell. Ancient dyers would have needed days or even weeks to collect and process thousands of snails, followed by a complex fermentation process to convert the precursors into stable dye molecules.
The dye bath preparation required skilled workers to control temperature, pH, and fermentation. Would dyers (whom we know historically to be frugal and sensible with materials) go through all of this and forgo the prized Tyrian purple that could be produced, in favor of a blue that could be easily created with plant dye?
A Proposal: Tekhelet as an Exhausted Bath
I propose a more economically plausible hypothesis grounded in practical dyeing logic and historical frugality: Rather than intentionally degrading a fresh and costly argaman vat to produce blue, ancient dyers may have produced tekhelet as a secondary product of the argaman dyeing cycle. While I am sure there will be a host of experts who will refute my findings, I am confident in stating them here from a dyer's point of view.
I am stating two key observations:
Color depletion: The reddish brominated component (6,6’-dibromoindigo) is present in smaller quantities in the mollusk than the blue-producing indigoid compound. After the first round of dyeing, resulting in purple, the subsequent rounds will naturally skew toward blue, as the purple fades and the remaining dye leans toward mono- or non-brominated indigo.
Layering effect: By using the same vat for multiple immersions, dyers could have created a layered blue tone over wool, much like overdyeing in plant-based indigo. The later baths, lacking sufficient bromine, would produce increasingly pure blue shades. These blues would not only be visually similar to indigo but also carry the ritual significance of marine origin.
This theory also aligns with a passage in the Tosefta (Menachot 9:6), which contrasts tekhelet with counterfeit kala ilan (plant-based indigo), acknowledging the visual similarity between the two but affirming the former’s divine origin.
From the Practical Eye of a Dyer
1. No experienced dyer would intentionally squander a substance as rare and valuable as mollusk-derived purple (argaman) merely to extract blue. This would be economically and practically illogical, especially given that similar blue hues can be obtained far more efficiently from plants like indigo or woad (kala ilan). We do see analogous practices in reverse: for example, when dyeing silk pink with safflower. In that case, the initial extract is a yellow pigment, abundant in nature and of low value, which must be carefully removed and discarded to access the rarer pink dye compounds. But safflower is a plentiful and inexpensive plant, making such a loss acceptable.
2. When it comes to dyeing logistics, every artisan who has maintained a blue vat knows how crucial it is to protect the anaerobic environment required for reduction. Indigo vats, especially those prepared through fermentation, must be kept covered and undisturbed between sessions to prevent oxidation and to preserve the delicate balance that allows for successful dyeing. The idea of deliberately exposing a vat, especially one as costly as a murex-based bath, to light or air simply to shift its tone to blue is not only counterintuitive but chemically precarious.
Conclusion and Visual Evidence
If we accept that tekhelet may have been produced from exhausted argaman vats, we open a door to reconciling historical economy, ancient textual evidence, and chemical plausibility. It removes the dilemma of wastefully sacrificing purple to produce blue and fits well with historical dyehouse practices where nothing went unused.
To illustrate this, I have included wool swatches dyed in the first, second, and third baths from a Hexaplex trunculus. The progression from deep purple to bluish purple to clear blue speaks for itself.
In a world where both symbolism and sustainability mattered, tekhelet as the afterglow of argaman may have been both a theological and practical truth.
Suggested Bibliography
Koren, Z.C. (1993). "The First Identified Biblically Described Dyeing Plant." Review of Progress in Coloration
Elsner, O. and Friedlander, M. (1984). "The Purple and Blue Dyes of the Ancient Mediterranean." American Dyestuff Reporter
Stillman, Yedida. The Costume of the Jews of Yemen (for mentions of indigo vs tekhelet practices)
Talmud Bavli, Menachot 42b
Tosefta Menachot 9:6
Pliny the Elder, Natural History, Book 9 (on Tyrian purple production)
Baruch Brandl and Michal Artzy (2006). "Phoenician Industrial Production at Tel Dor." In Beyond Babylon: Art, Trade, and Diplomacy in the Second Millennium B.C.
Sukenik, Eleazar L. "Ancient Fragments of Purple-Dyed Textiles." Bulletin of the Jewish Palestine Exploration Society.
