Tekhelet 101

A fisherman in the 19th century wants to impress his shipmates. He reaches into the water, pulls out a snail, breaks it open and smears his shirt with the contents. To everyone’s amazement, the yellowish streak dramatically changes color in the bright Mediterranean sun. The secret of tekhelet is revealed.







One should always be heedful of the commandment to wear tsitsit, for the Torah equated and connected all other mitzvot with it, as it is written ‘And you shall see it and remember all of the commandments of Hashem and you shall do them.’ (Rambam, Hil. Tsitsit, 3;13)

The story of the search for the source for the dye tekhelet – Biblical blue – is one of intrigue, deception, and deduction. It weaves together clues from Torah scholarship, archeology, and chemistry, and its major players include a great Chasidic Rebbe, a former Chief Rabbi of Israel, archeologists, marine biologists and chemists.

Biblical Blue





“And the Rabbis said: Why does the Torah enjoin us regarding tekhelet? Because tekhelet resembles sapphire, and the Tablets were of sapphire, to tell you that so long as the people of Yisrael gaze upon this tekhelet they are reminded of that which is inscribed on the Tablets and they fulfill it, and so it is written, ‘And you shall see it and remember.’
(Mishnat Rabbi Eliezer, ch. 14).

In ancient times purple and blue dyes derived from snails were so rare and sought after that they were literally worth their weight in gold. These precious dyes colored the robes of the kings and princes of Media, Babylon, Egypt, Greece and Rome. To wear them was to be identified with royalty.

Twice daily we read:




“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 15:37-39)

We are commanded to place a thread of blue on our tsitsit as a constant and conspicuous reminder of our stature. We are banim lamakom, noble sons of the King of the Universe, always pursuing His mitzvot.

The History




“And now we have only white, for the tekhelet has been hidden.” (Bemidbar Raba 17:5)


A coin from the city of Tyre dated 200 C.E. depicts the legend of Hercules’ dog discovering the Murex

The Mediterranean coast was the center of the dyeing industry in the ancient world. “Tyrian Purple” came from the port of Tyre in Phoenicia (now southern Lebanon). The Phoenicians made their wealth trading in the dyestuff, and dye houses were ubiquitous in the region. Because of its lucrative nature, purple and blue dyeing slowly came under imperial control. The Romans issued edicts that only royalty could wear garments colored with these dyes, and only imperial dye houses were permitted to manufacture it. This apparently drove the Jewish tekhelet industry underground. Later, with the Arab conquest of Eretz Yisrael (683 CE), the secret of tekhelet was essentially lost, the dyeing process forgotten.

The Chilazon




“Rabbi Meir said: Whoever observes the mitzva of tsitsit, is considered as if he greeted the Divine Presence, for tekhelet resembles the sea, and the sea resembles the sky, and the sky resembles God’s holy throne.” (Sifre, Shelach, 15:39)

tekheletseashellThe Biblical commandment to wear tsitsit is still observed today, but the prominent blue thread has all but been forgotten. What has remained are passages in the Talmud describing the source of the blue dye – a snail known as the Chilazon. This marine creature had a shell, could be found along the northern coast of Israel, and its body was “similar to the sea.” The dye’s color was “similar to the sky and sea,” it was steadfast, extracted from the snail while still alive, and was indistinguishable from a dye of vegetable origin, called kala ilan (indigo).

The Rediscovery





“There is an obligation, upon all who are capable, to search for it [the Chilazon], in order to bring merit upon Israel with this commandment, which has been forgotten for the last several centuries. And he who succeeds in this will surely be blessed by the God of Israel.” (Rabbi Gershon Henoch Leiner, the Radzyner Rebbe)

In 1858 the French zoologist Henri de Lacaze-Duthiers found that three Mediterranean mollusks produced purple-blue dyes. One, Murex trunculus, was determined by him (and other scientists, archeologists and historians) to be the source of the ancient Biblical blue.

In the same century, unaware of Lacaze-Duthier’s findings, Rabbi Gershon Henoch Leiner – the Radzyner Rebbe – set out on an expedition to search for the lost Chilazon in a grand effort to restore tekhelet to the Jewish people. He was convinced that a certain squid fit the descriptions of the Chilazon. However, unable to produce a blue dye from the black ink released from this squid, he turned to an Italian chemist, who provided him with a method. Within two years, ten thousand of the Rebbe’s followers were wearing blue threads on their tsitsit. The Rebbe published two books to counter the strong opposition from other Torah scholars who did not agree with the Rebbe’s conclusions.



“The [squid] blood … is mixed with iron filings and a snow white chemical called potash. After keeping it on a large powerful fire for some four or five hours, until the flames burn outside and inside as the fires of Gehenna, the mixture fuses…”  (from a letter sent by the Radzyner dye master to Rabbi Herzog)

Chief Rabbi of Ireland, Rabbi Isaac Herzog

Chief Rabbi of Ireland, Rabbi Isaac Herzog

In 1913 the Chief Rabbi of Ireland, Rabbi Isaac Herzog (later Chief Rabbi of Israel), wrote a doctoral dissertation on the subject of Hebrew Porphyrology (the study of purple – a word he coined). When he sent samples of the Radzyn tekhelet to chemists and dye experts for analysis, the dye was found to be inorganic – a synthetically manufactured color known as Prussian Blue. Refusing to believe that Rav Gershon Henoch had purposely misled his constituents, Rav Herzog studied the Radzyner dyeing process. The truth soon became apparent. The process called for subjecting the squid ink to intense heat and then adding colorless iron filings to the mixture. This produced the blue color which indeed appeared to come from the squid ink. In fact, under these conditions, virtually all organic substances would yield the same blue dye – the squid was not an essential component. The Rebbe had apparently been misled by an unscrupulous chemist.

As an interesting side note of history, during World War II with the destruction of East European Jewry, the tekhelet factories of Radzyn were ruined and the process lost. When the survivors of Radzyn made their way to Israel after the war, they asked Rav Herzog for the correspondence between himself and the Radzyn dye makers, and through those letters reestablished a tekhelet industry in Israel which still flourishes to this day. Thus Rav Herzog is responsible both for discrediting Radzyn’s tekhelet and at the same time for rescuing their process from destruction.


The vein is removed… and to this salt has to be added… three days is the proper time for it to be steeped, and it should be heated in a leaden pot with 50 lbs. of dye to every six gallons of water. (Pliny the Elder, Natural History 9.61.133, first century BCE)

Rav Herzog knew of the work done by Lacaze-Duthiers and others, and realized that all the evidence pointed to Murex trunculus as the most likely candidate for the tekheletsource. Two problems, however, prevented Rav Herzog from positively identifying that snail with the Chilazon. First, the dye obtained from the trunculus was purplish-blue, not pure blue as tradition maintained. Second, this snail has an off-white shell with stripes of brown, hardly fitting the Talmudic description of the Chilazon as appearing similar to the sea.

Current research has supplied the solutions to these objections. The shell appears off-white with brown stripes when it is out of the water, cleaned and polished. In its natural element, however, trunculus is covered with a coat of sea fouling the color of the ocean. Everything in its vicinity is covered with the same fouling, making it almost impossible to distinguish the snail from the sea bed on which it is found. The Talmud’s description is of the Chilazon in its natural habitat!

The riddle of producing a pure blue color from the snail was serendipitously solved. While researching the methods used by the ancient dyers, Prof. Otto Elsner, of the Shenkar College of Fibers, noticed that on cloudy days, trunculusdye tended towards purple, but on sunny days it was a brilliant blue! He found that at a certain stage of the dyeing process, exposure to sunlight will alter the dye, changing its color from purple to blue. To the dye masters of old, working in the bright Mediterranean sunlight, this was certainly no secret.

The Chemistry of Tekhelet

dyecolor2Inside the hypobranchial gland of the snail, the precursors to the dye exist as a clear liquid. When these are exposed to air and sunlight in the presence of the enzyme purpurase, which also exists within the gland, they turn into the dye. Purpurase quickly decomposes, so for this reaction to take place, the gland must be crushed soon after being taken from the live snail, in accordance with the Talmudic passage that the tekheletis taken from the Chilazon while still alive. The liquid from the trunculus, produces a mixture of dibromoindigo (purple) and indigo. These molecules must be put into solution for them to bind tightly to wool. In this state, if dibromoindigo is exposed to ultraviolet light, it will transform to indigo, turning the trunculus mixture from purplish-blue to pure blue.

Murex Trunculus




“Have mercy on us and rebuild Your city speedily in our days, and bring us to peace, to our Holy Land, and let us merit the return and revelation of the Chilazon, that we may be privileged to fulfill the commandment of tekhelet in tsitsit.”
(from the prayers of Rabbi Nachman of Bratslav)

The evidence for identifying the Murex trunculus as the source of tekhelet is decisive, and goes beyond merely fitting the general descriptions of the Chilazon as found in the Talmud:

  • Shard of a vat found at Tel Shikmona from the Bronze Age, 3200 years old. The chemical composition of the stain is identical to the dye obtained from Murex trunculus.

    Shard of a vat found at Tel Shikmona from the Bronze Age, 3200 years old. The chemical composition of the stain is identical to the dye obtained from Murex trunculus.

    The Jerusalem Talmud (as quoted by the Raavyah) translates tekhelet asporphiron (the Latin and Greek name for trunculus-like shells). Pliny and Aristotle describe these shells as the source of the ancient dyes.

  • The Talmud indicates that true tekhelet is indistinguishable from the blue dye of vegetable origin – kala ilan (indigo). The dye ultimately derived from trunculus is molecularly equivalent to indigo.
  • Extensive marine biological surveys have revealed that the only snails in the Mediterranean which produce stable dyes are those of the Murex family. The dye obtained from trunculus is very stable and steadfast, which accords with the Rabbinical description of tekhelet.
  • dye industryArcheologists in Tyre and elsewhere uncovered mounds of Murex shells dating from the Biblical period which were broken in the exact spot necessary to obtain the dyestuff. Chemical analysis of blue stains on vats from 1200 BCE reveals patterns consistent with those of modern day trunculus.
  • When listing the precious commodities used in building the Mishkan (tabernacle), the Torah consistently includes tekhelet along with gold, silver, and other familiar materials, recognized by all for their worth. Yechezkel speaks of the tekhelet from Tyre and the “Isles of Elisha”, and the Megillah tells us that in Persia, Mordechai wears royal clothes made of tekhelet. Surely, the Torah is referring to that same valuable dye commonly used by royalty throughout the rest of the ancient world.

P’til Tekhelet



“The revelation of the Chilazon is a sign that the redemption is shining near.” (Divrei Menachem 25)

Recently much has been accomplished to reestablish the tekhelet dyeing process. Dr. Irving Ziderman, of the Israel Fiber Institute, has published a number of articles describing the scientific aspects and religious implications of the trunculus dye. Rabbi Menachem Borstein has written a book surveying the relevant Jewish legal aspects of tekhelet, and Prof. Tzvi Koren, of the Shenkar College of Fibers, has done rigorous chemical analysis of the dye from present day snails as compared with samples from archeological artifacts dating back 3,200 years. Until a few years ago, however, tekhelet could be found only in the library or the laboratory.

In 1985, Rabbi Eliahu Tavger of Jerusalem began researching and writing a book about ritual fringes – the tsitsit – and became convinced that authentic tekhelet had been discovered. Determined to actualize his newfound knowledge, and after much trial and error, he succeeded in applying the process according to the halakha from beginning to end. Based on Rabbi Tavger’s pioneering work, P’til Tekhelet was formed in an effort to provide tekhelet to the general public. Today, after more than 1,300 years, tsitsit are again being made with the elusive thread of tekhelet.

P’til Tekhelet – The Association for the Promotion and Distribution of Tekhelet – is a non-profit organization based in Israel. P’til Tekhelet provides educational programming and resources pertaining to Tekhelet, and produces Tekhelet for tsitsit. The association is comprised of a small group of individuals whose work is done lishma – for the express purpose of making tsitsit as the halakha requires.