Criteria for Identification


Tekhelet & the Hillazon


Prepared by Mois A. Navon





Talmudic Description

Physical Evidence


Tzaydei hillazon  - The fishers of the hillazon are from Haifa to Sulamot Shel Tzur (the Ladders of Tyre). (Shabbat 26a).

· Archeological digs show remnants of the dyeing industry on the Northern coast of Israel through the southern coast of Lebanon. (Royal Purple, p.149-157).

· Digs near Haifa and Tyre and beyond, revealed mounds of Murex shells (broken to access their dyestuff) - some up to one hundred yards long and several yards thick. (Royal Purple, p.24, p.151-5; Ziderman, p.438; Twerski, p.82).


Potzeia - One who breaks open a hillazon ... (Shabbat 75a).

Go and learn [about the clothes of the Jews in the desert] from the hillazon, all the time that it grows, its shell (nartiko) grows with it (Shir HaShirim R. 4:11).

· R. Herzog explains the use of the verb potzea to mean, “break open” - as in a nut. (Herzog, p.57).

· The Murex snail is a hard-shelled Mollusk, which must be broken open to obtain the dyestuff. (Royal Purple, p.180; Ziderman, p.430).

· The shells found in the archeological digs were broken in the exact spot necessary to obtain the dyestuff. (Ziderman, p.438).


“The hillazon is this: its body is like the sea, it’s creation is like a fish, it comes up once in 70 years and with its blood one dyes tekhelet - due to this it is expensive” (Men. 44a).

· The vagueness of these descriptions make them ineffective for use in identification - other more indicative signs could have been given, if that was the intention of the Gemara.  Each point comes to explain the conclusion of the statement that “the dye is expensive” (Rock, n.57).

· The declaration that “it is expensive” is simply out of place in a formal halachic definition.  It would, however, make sense as part of an explanation to consumers curious as to the reason for the exorbitant price. (Herzog, pp.66-7).


Briato - Its creation is similar to that of a fish. (Men. 44b).

· Briah - a general classification of creatures - “like fish” that live in the ocean, so too do Murex snails. (Rock, n.57).

· Murex snails are spawned from eggs, just like fish. (Twerski, p.98).

Body Color

The body of the hillazon is like the sea. (Men. 44a).

· The snail shell takes on a blue-green color due to the sea fouling organisms covering them.  In any case, the shell is always the same color as the seabed in which it is found. (Sterman, p.69).  Biblical and Talmudic references to “sea” often refer to “sea-bed” (e.g. Yishaya 11:9). (Rock, p.15).

· It is a more than reasonable assumption that the Gemara is referring to the shell as it looks when it is caught (and not after it has been polished). (Ziderman, p.430).

70 Years

…[the hillazon] comes up once in 70 years (Men. 44a).

· “Once in 70 years” (an oft-used Talmudic expression meaning “once in a lifetime”) it washes up; otherwise, it must be fished out, thus adding to its cost.

· “Nevuzaradan left … the tzadei hillazon” (Shabbat 26.) - for the sake of the king’s garments (Rashi on ibid.).

· The Rambam (Hil. Tzitzit 2:2) makes no reference to “70 years”.

Dye Extraction

One is more pleased that it should be alive, so that the “blood” should be clear/successful (Shabbat 75a) - the “blood” from the live [hillazon] is better than from it dead. (Rashi on ibid.)

· Inside the hypobranchial gland of the snail, only the precursors to the dye exist as clear liquid. (Royal Purple, p.183, 188, 214).

· The chemistry of the dye formation in the Murex requires a specific enzyme (purpurase), which quickly deteriorates upon the snail’s demise. (Sterman, p.68).

Dye Color

Tekhelet resembles the color of the sea, and the sea the sky…(Men. 43b).

God said: I have distinguished in Egypt between the drop of [semen that was to become] a firstborn and that of a non-firstborn, I will exact retribution from he who attaches kela ilan to his cloth and claims it is tekhelet (Baba Metzia 61b).

· Kela Ilan has consistently been identified as indigo (Aruch), which is blue.

· The blue dye obtained from the Murex trunculus snail is molecularly equivalent to the dye obtained from the kela ilan plant. (Royal Purple, p.175).


Dye Additives

How is Tekhelet made? By placing the blood of the hillazon and samanim (chemicals) in a pot to boil (Men. 42b) - samanim are only to fix the dye into the fabric (Noda BeYehuda).

The process of making dye from Murex trunculus:

·        The dyestuff is boiled along with a strong base to dissolve the snail meat and to create the chemical environment for reduction.

·        The solution is then reduced to make the dye water-soluble enabling it to take to wool (i.e., typical vat-dyeing).

·        An acid is then added to neutralize the strong basic solution in order to prevent the dye solution from damaging the wool.

Dye Testing

How is Tekhelet made? … then we take out a little in an egg shell and test it on a piece of wool (Men. 42b).

As with all vat dying, the Murex dye solution is yellowish in the vat and its final color can only be determined when the dye oxidizes in the wool.  Since the resultant color can range from blue to purple, the dye must be tested to determine if it has been sufficiently exposed to ultraviolet light.

Dye Quality

Lo ifrad hazutei - If its color is permanent then its valid (Men. 43a) - its dyeing is well known for its steadfast beauty and does not change (Rambam, Hil Tzitzit 2:1).

· The Murex dye binds very tightly to wool, and is among the fastest of dyes known to the ancient world. (Sterman, p.67).

· Three days in strong bleach has no effect. (Twerski, p.91).


“Treasures buried in the sands”(Dev. 33:19) refers to the hillazon. (Megilla 6a).

Murex trunculus burrows into the sands and sediment on the sea floor. (Royal Purple, p.181, p.190; Ziderman, p.429; Twerski, p.85).



Raavya quotes the Yerushalmi identifying tekhelet with the Greek word porphyra.

Porphyra is the Greek word used to refer to Murex snails. (Sterman, p.68).




R. Isaac Herzog, The Royal Purple and The Biblical Blue, Keter, 1987.

Dr. Baruch Sterman, The Science of Tekhelet, Tekhelet: Renaissance of a Mitzvah, YU Press, 1996.

Dr. Yisrael Ziderman, Reinstitution of the Mitzvah of Tekhelet in Tzitzit, Techumin, Vol. 9.

R. Chaim Twerski, Identifying the Chilazon, Journal of Halacha and Contemporary Society, Num. XXXIV.