Techeles, the blue strings the Torah requires Jews to wear on their ritual tzitzis garments, has long been thought of as a “dead” mitzvah. Sometime in the 7th century apparently (possibly due to the Arab conquest of Israel) Jews stopped producing techeles strings and the identity of the chilazon, from which the blue dye originates, was subsequently lost.

 However, 1,200 years later, interest in the mitzvah reawakened. In the 19th century, anticipating the building of the Third Temple, the Radzyner Rebbe traveled to an aquarium in Naples, Italy and identified the chilazon as the Sepia officinalis, a certain kind of squid.


 In 1913 Rav Isaac Herzog, who later became Israel’s first Ashkenazic chief rabbi – and whose 50th yahrzeit will be commemorated this year – wrote his PhD dissertation on the chilazon’s identity. He calls the Murex trunculus snail the “most likely candidate” but, because of unsolved questions, did not come to a definitive conclusion.

Today P’til Tekhelet, an Israeli organization founded in 1993, provides techeles to tens of thousands of Jews around the world based on Rav Herzog’s research.

Dr. Ari Greenspan, a co-founder of P’til Tekhelet, recently spoke to The Jewish Press.

The Jewish Press: On one foot, please relate the genesis of P’til Tekhelet?

Dr. Greenspan: In 1985 Rabbi Eliyahu Tavger of Jerusalem began looking into techelet as a matter of halacha lema’aseh. A series of circumstances brought me, Joel Guberman and Baruch Sterman [the other P’til Tekhelet co-founders] together and we went scuba diving to get the snails [Murex trunculus] with Rabbi Tavger.

The renewal of the ancient dying technique was unchartered waters, and it took us a year to figure out how to make those first 10 sets of techelet – the first in close to 1,300 years. People then began asking us for techelet and before we knew it we had hundreds of people on a waiting list.

How do you know the Murex trunculus is in fact the chilazon?

Rav Herzog was convinced, on an intellectual level, that the murex was the source of techelet. But he was left with three major problems that he mentions in his doctoral thesis: 1) He was told by the preeminent French chemist on dyes that the color from the murex was not permanent, which is the defining characteristic of techelet; 2) The color they were able to get was only purple, while the definition of techelet is sky blue; and 3) The only murex snail he saw was a dead polished murex. It was cream colored, while the Talmud talks about it being “similar to the sea” [blue-green].

However, all three of these objections are based upon mistaken evidence or advice. 1) The color blue we derive from the murex is the most permanent natural color in existence. We have done chemistry tests to prove this. The facts were simply told to Rav Herzog incorrectly. 2) Thirty years ago Professor Otto Elsner discovered by accident that if the liquid extracted from the murex is exposed to sunlight, the molecule of color changes from dibromoindigo (puple) to indigo (blue). 3) Had Rav Herzog seen a live snail and not a polished dead one he would have seen its shell covered with a bright blue/green color, just like the “color of the sea.”




Tzitzis with techeles tied according to (L-R) the Radzyner Rebbe/Chabad; the Rambam (one interpretation); the Vilna Gaon; the Sefer HaChinuch; the Raavad; Rav Amram Gaon; and the Rambam (Yemenite tradition).

How can you be sure that the dye extracted from the Murex trunculus is the real techeles?

During Talmudic times there was a fake techelet that was cheap to make. The Talmud says it was so similar to the real thing that “only God could differentiate between them.” This fake techelet, called kala ilan, is identified by the Rambam and others as the indigo plant. Now, it turns out, that murex-derived indigo and kala ilan-derived indigo are molecularly identical. No wonder the Talmud says only God could distinguish between them!

Having said that, we cannot be sure the Murex trunculus is the real chilazon. However, when one looks at the entire picture, we can say that the identification of murex as the source of techelet fits the Talmudic, halachic, archaeological, historical, biological and chemical description.

Why haven’t those rabbis regarded as gedolim given their approval to your project?

Why do you say this? Many have. There are some significant figures in the halachic world wearing it publicly and many others who wear it in a private manner so as not to make a public statement as long as it is not worn by all of Am Yisrael. I find that intellectually honest people who take the time to really learn this sugya have a very  difficult time walking away not being convinced this is the real techelet.

Which rabbis, then, support you?

I am not sure how to handle this. First, no matter what names I give you there will always be others who don’t or don’t yet wear techelet. Second, many people, in the U.S. in particular, have not even looked into this issue and, as a result, their practice of not wearing techelet is no proof of disagreement – “lo ra’inu eini raya.”

That being said, the following are just some of the rabbis who wear techelet: The well-known posek Rav Zalman Nechemia Golderg; the son and brother of Rav Shlomo Zalman Auerbach, z”l; Rav Simcha Kook from Rechovot; Rav Shlomo Dichovsky of the Bet Din Hagadol; Rav Amram Opman of the Eida Chareidis in Yerushalayim; Rav Hershel Schachter [from Yeshiva University]; and Rabbi Dr. Abraham Twerski.

Some people claim that someone who doesn’t wear techeles is violating the commandment of “ba’al tigrah,” detracting from the Torah’s commandments? Do you agree?

Some poskim might say so. One should address this issue with his own posek. It is a complicated halachic issue.

Some people argue that thousands of people are potentially not fulfilling the mitzvah of tzitzis if your organization is wrong and they are wearing false techeles.  What is your reply?

The Radzyner Rebbe already addressed this question 120 years ago. He writes that one loses nothing by wearing techelet, for even if it is not really techelet, the Talmud tells us it is “no worse than wearing white [strings].”

Where can someone go to learn more about this topic?

Our website,

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Elliot Resnick is the former chief editor of The Jewish Press and the author and editor of several books including, most recently, “Movers & Shakers, Vol. 3.”