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Does the oral tradition that identifies the hilazon as the source of tekheles necessarily indicate that one could not create the indigo-colored wool by other means? The gemara certainly indicates that the color-equivalent, plant-derived kala ilan is not valid (e.g. Menachot 40a, 43a, Bava Metzia 61b) but it also implies that this particular dye was not as fast and permanent as true tekhelet (and therefore, implicitly, was not its molecular equivalent). If that is the case, if one was able to create a dye that was chemically indistinguishable from true tekhelet, considering that torah shebiksav (the Written Law) never explicitly mentions the source of tekhelet, might that not also be acceptable?

  • Can you link to the gemara discussing kala ilan? Does it only dismiss it for that reason? – Isaac Kotlicky Apr 16 '15 at 2:15
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    Aren't you confusing the test for authenticity with a reason for it? – user6591 Apr 16 '15 at 2:31
  • I don't mean to say that that's the gemara's intent. I'm just curious to know if there is anything explicit to say that the source matters or just the substance. It's implicit from that there is a test that the substances differ. But what if we discover something that does not. (As opposed to if we invent chemically indistinguishable artificial ham, the torah clearly and explicitly forbids only the source, not the chemical compounds.) – Loewian Apr 16 '15 at 2:59
  • This is hypothetically very nogeia l'maaseh nowadays because, if artificially-dyed techeles is acceptable, and if the Tekhelet Institute is right that the dye is just murex-derived indigo, artificial indigo (used in blue jeans) is dirt cheap. – Loewian Apr 16 '15 at 3:03
  • Note that Chazal never complain about another animal source of Tekhelet, only a plant one. It seems that either they knew of no other one or that all animal sources are Kosher. – Double AA Apr 16 '15 at 3:46
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This requirement is stated in the Tosefta and Meseches Tzitzith

Tosefta Menachoth 9:16

"תכלת אין כשרה אלא מן החלזון הביא שלא מן החלזון פסולה."

Tekheleth is only valid from the חלזון ; if one used a dye not made from the חלזון it is invalid.”

מסכת ציצית פרק א הלכה י

שאין צובעין תכלת אלא בחלזון.

We only dye תכלת with a חלזון

from: https://www.techeiles.org/harav-meir-halevi-hellman-levush-haaron/

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R. Yisrael Lipschitz writes the following in his introduction to Seder Moed:

הכלל העולה דבין ציצית ובין בגדי כהונה א״צ חלזון דוקא אבל צריך בשניהן שיהיה מראה (היממעלבלויא) שאינו משתנה מיפיו ע״י בדיקה שהזכיר הש״ס

The principle that emerges is that both by tzitzit and by the priestly vestments it is not necessary to specifically use a chilazon. But it is necessary by both that the color be sky-blue that does not deteriorate from it’s beauty via the test mentioned in the Talmud.

R. Joseph Ber Soloveitchik (as recorded in שיעורי הרב הגאון רבי יוסף דב הלוי סולוביצ׳יק זצ״ל על עניני ציצית עניני תפילין והלכות קריאת התורה) reached the same conclusion:

ובה״ב כיצד צובעין תכלת של ציצית לוקחים וכו׳ דם חלזון וכו׳ אבל בה״א לא הזכיר חלזון כשהגדיר מהו התכלת רק בה״ב כשהזכיר איך עושים אותה בפועל ומשמע דלא הוי חלזון הללמ״מ אלא שבמציאות הוא הי׳ הצבע היחיד שהי׳ מתקיים שהי׳ עינו השמים והים אבל איה״נ דאילו הי׳ לנו בזה״ז צבע סינטטי אחר שהי׳ מתקיים הי׳ כשר לתכלת

And in Law 2: “How do we dye the techeilet of tzitzit? Take... the blood of the chilazon...” But in Law 1 chilazon is not mentioned when techeilet is defined; only in Law 2 when mentioning how to actually make it. This implies that chilazon is not a law to Moses from Sinai; rather, it was in reality the only dye that was steadfast whose color was [that of] the sky and the sea. But indeed if we had nowadays another synthetic dye that was steadfast it would be valid for techeilet.

(Elisions in original)

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