The mystery of the blue thread has fascinated people for thousands of years. In the Torah (Bamidbar/Numbers 15:38-40) the Lord spoke to Moses and instructed the Israelites to attach fringes on the corners of their garments.

Speak unto the children of Israel, and bid them that they make them throughout their generations fringes in the corners of their garments, and that they put with the fringe of each corner a thread of blue (techelet  פְּתִיל תְּכֵלֶת).

And it shall be unto you for a fringe, that ye may look upon it, and remember all the commandments of the LORD, and do them; and that ye go not about after your own heart and your own eyes, after which ye use to go astray; that ye may remember and do all My commandments, and be holy unto your God.

The Torah does not explain how to dye the thread blue, nor what the source of the dye should be. Typically, these instructions are discussed in the Talmud. The talmud in Menachot gives us some clues as to the source of the dye:

Our Rabbis taught: The hillazon resembles the sea in its colour, and in shape it resembles a fish; it appears once in seventy years, and with its blood one dyes the blue thread; and therefore it is so expensive.

So now we have some clues on what we are looking for:

  1. The source of the dye is the chilazon.
  2. The color of its body is like the sea.
  3. Its form is like a fish.
  4. It comes up once in 70 years.
  5. Its blood is used for techelet.
  6. It is expensive.

Let’s look at each requirement and understand what creature we should be looking for.

1. The source of the dye is the chilazon.

This point does not contribute a lot to our search, but it does tell us that the source is not a plant, like so many other dyes. We do know that claiming that tzitzit dyed with indigo and claiming it as authentic, was forbidden.

2. The color of its body is like the sea.

Photo by Raul654

Sepia Officinalis Photo by Raul654

Great, but what does the sea look like? It is easier to say the color of the sky, because there is a range of blues (as long as we don’t include sunrise and sunset). The sea is vast and contains many colors. Colors can be subjective and we need a further clarification on this point. We also need to understand the word “body”, because many sea creatures have an inside body and a shell, or outer body.

Some say that the Murex Trunculus has sea foulings on it, which make it appear like the bottom of the sea. But I don’t think that if you were describing an object, you would tell someone about an outer coating that appears on it sometimes, especially since everything has sea-fouling on it. Even Rav Herzog wrote about the Murex: “To our disappointment behold this species is not at all aligned to “Its Body Resembles The Sea.”

The Sepia Officinalis though, has the ability to disguise itself and look like its surroundings. Its skin contains  chromatophores, leucophores and iridophores, which are filled with ink that not only change color to camouflage itself or send messages to predators or mates, but also change the texture of the skin. This quality is also used for mating purposes. It is not sea foulings that are stuck on the outside as is the case with Murex Trunculus.

3. Its form is like a fish.

Below are three pictures of the three leading candidates for the chilazon. Which do you think resembles a fish? Keep in mind that the source does not say that the chilazon is “classified” as a fish, or what according to “halacha” is a fish, but which has a “form” similar to a fish.


4. It comes up once in 70 years.

The Radziner rebbi explains that the chilazon was probably easily found, based on his understanding of Shabbat 26a and 75a. So, in order to understand the requirement that it come up every 70 years and that it was always easily found, he understands it to mean that there are cycles where the sepia officinalis multiplies in abundance and the rest of the time, it is available to skilled people with nets who can catch them. The Murex does not have cycles when their are found in abundance.

5. Its blood is used for techelet.

Not exactly “blood”. In the case of the sepia officinalis, it is the ink that the cuttlefish uses to protect itself, sneak up on prey and use it for mating. The murex uses a mucous from a gland.

6. It is expensive.

Techelet from any of the three candidates would be expensive to produce. Since Janthina is not used today for making techelet, we can only compare techelet made with Sepia Officinalis and Murex Trunculus.

Below are approximate prices for tzitzit for comparison purposes.

Machine made tzitzit strings $4.00
Radzin strings $20.00
Ptil Tekhelet $70.00

7. The chilazon is caught with nets.

Catching snails with a net? I don’t think so. An argument is made that the snail are caught by lowering baskets into the sea with bait inside. A mesh is put on top so the snails don’t fall out when the baskets are raised to the surface. There traps available online for snail. This does not sound convincing to me.

8. The chilazon has tentacles bent like hooks (Mishnah in Keilim).


Photo by DAVID ILIFF. License: CC-BY-SA 3.0

Again, this is not a red herring that is stuck to a wall, the Sepia Officinalis has the tentacles that look like hooks. Do the other candidates? Take a look at the comparison below. When I find images of the Murex and Janthina with the snail intact, I will add them for a more accurate comparison.



9. Treatment for hemorrhoids

From Vitality Magazine:

With our hectic modern lifestyles, increased environmental toxicity, and gradual disconnect from nature’s cycles, it is no wonder that Sepia Officinalis is often called upon by the homeopathic practitioner. Derived from cuttlefish ink, Sepia has a broad range of action over the female organism, and is one of Samuel Hahnemann’s greatest contributions to the homeopathic pharmacopoeia.

Conditions That Benefit From Homeopathic Sepia

Circulatory ProblemsSepia women, with their innate desire to keep moving, are especially prone to stasis and stagnation. Apart from overall chilliness, and especially coldness of the extremities, they may likely suffer from varicose veins and bleeding, protruding hemorrhoids (often accompanied by constipation).

10. Hides in the sand

The cuttlefish are known to burrow into the sandy sea bottom during the day and to use this hidden  location to catch their prey. The Murex tuck their bodies into their shells on the sea bottom, but do not technically burrow into the sand.

11.Dye is better while chilazon is alive

The sepia officinalis produces enzymes while living, which stop when the it dies. At that point the ink gets mixed with impurities. This was known to the Radziner rebbi and can also be confirmed with marine experts today.

The Murex Trunculus secretions that are used for dying also require fresh secretions, but can use the mucous for up to two hours after death before it deteriorates.

12. Hard shell

The gemara discusses the issue of breaking or crushing the chilazon to extract the dye. Rashi says that the person squeezes the chilazon in their hand to get the dye out.

13. Shell grows with it.

Yes, yes and yes. Cuttlefish have an internal shell, Murex and Janthina have outer shells.


14. Blood is black (Rambam)/blood is color of techelet (Rashi)

The black ink of the cuttlefish is well known (fishermen call them “inkfish”) and after the solution is processed, it turns into blue. The secretions from the murex snail are clear and at no point does the dye turn black or blue, unless it is left out in the sun.

15. Techelet made with the chilazon passes the k’la ilan test

While I have not performed this test myself, I understand that the techelet from Murex Trunculus is identical to indigo-dyed wool and if wool dyed in indigo would fail, so would the techelet made with Murex Trunculus. It looks like they discovered a very expensive way of making indigo. If on a molecular level the two are the same and the Murex techelet is indistinguishable from indigo, I suspect that Murex was NOT commonly used to make techelet, but it was likely used to make purple dye. That is wht there are mounds of Murex shells found in archeology digs.

16. Snake-like extensions.

Again, check the photos above.

17. Jumps about when caught hastening its death (Tosafot Shabbat 75a).

Does this look like something that would jump around when caught?









P.S. I just read Zvi C. Koren’s response to The Great Tekhelet Debate—Blue or Purple? by Baruch and Judy Taubes Sterman. Besides his comments on his analysis of the only archeological fabric that has ever been found that might possibly be techelet, he has a very interesting commentary on the availability of chemicals needed to make blue techelet prior to the 1930s.

…the authors’ organization uses a method known since the 1930s, which was also used by my late colleague, Prof. Elsner, that transforms much of the red and violet components in the dissolved pigment to the blue indigo dye by exposing the dye solution to sunlight. This method does not produce “pure” indigo, as the authors state; my chemical analyses show that the other components are still present. In addition, this technique is performed by first dissolving the pigment with a strongly reactive synthetic chemical reagent not available in antiquity.

To be continued…

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