Shelach Lekha (שלח לך – Send for yourself)
Numbers 13:1–15:41 and Joshua 2:1–24
Moses sends twelve explorers into Canaan; upon their return, ten of them deliver an alarming report. Frightened, the people refuse to take possession of the land and are consequently condemned to forty years of wandering in the desert. Forty years later, Joshua in turn sends two spies to Jericho, the key to entering Eretz Israel (Talmud, Sotah 34b). Their successful mission leads to the conquest of Canaan. In both narratives, one motif recurs: the cord[¹]. The blue thread of the tsitsit, and the scarlet cord hung by Rahav at her window.
Numbers 15:38
דַּבֵּר אֶל-בְּנֵי יִשְׂרָאֵל… פְּתִיל תְּכֵלֶת
Speak to the children of Israel, and tell them to make fringes on the corners of their garments throughout their generations, and to put a thread of blue on each corner fringe.
The method for producing the tekhelet (תְּכֵלֶת – indigo blue) was lost over the centuries. In the 19th century, Mediterranean fishermen reported that their garments turned blue after handling certain sea snails. In 1882, intrigued by these accounts, Rabbi Gershon Hanokh Henikh Leiner[²] applied his dual expertise in Torah and natural sciences in an attempt to identify the animal used for dyeing the tsitsit. His investigation — mistakenly — led him to identify the common cuttlefish (Sepia officinalis) as the ḥilazon (חילזון – the biblical snail).
In 1968, Israeli chemist Otto Elsner (1936–2022) demonstrated experimentally that the Hexaplex trunculus produces a blue dye through a photochemical reaction. In 1980, the Ptil Tekhelet team in Israel, led by Rabbi Eliezer Yosef Tavger[³], succeeded in reproducing this process. The method was validated, and a breeding farm for Hexaplex trunculus[⁴] was established in Haifa.
Today, several halakhic authorities[⁵] recognize the validity of modern tekhelet. Figures such as Rabbi Hershel Schachter, Rabbi Zalman Nechemia Goldberg, and Rabbi Shlomo Machpud consider the accumulated evidence⁶ strong enough to restore this forgotten mitzvah.
[¹] Joshua 2:18 mentions a “cord of scarlet thread” (תִּקְוַת חוּט הַשָּׁנִי); Joshua 2:21 repeats “the scarlet cord” (תִּקְוַת הַשָּׁנִי).
The word תִּקְוָה (tikvah), from the root ק–ו–ה (“to hope” or “to stretch a line”), conveys a sense of active, tension-filled anticipation. In kabbalistic tradition, this thread is associated with protection against the evil eye. Two words, two registers: the text could have chosen the generic hevel (חֶבֶל – simple rope), yet deliberately selects ptil (פְּתִיל) — a twisted, ritualized thread — a sacred reminder of the covenant. And on the other hand, tikvah bears the full weight of longing and redemptive hope.
[²] Rebbe Gershon Hanokh Henikh Leiner (1839–1891), Hassidic master of Radzin and a pioneer in reviving the search for tekhelet in the 19th century.
[³] Rabbi Eliezer Yosef Tavger (1948–2022), physicist and Torah teacher. In 1988, he performed the first halakhic tekhelet dyeing in over 1,300 years.
[⁴] Hexaplex trunculus (also known as Murex trunculus): a marine gastropod identified as the biblical ḥilazon. The Talmud (Menachot 42b–44a) provides clues: “its body resembles the sea” — it lives in the Mediterranean and has an iridescent shell; “it resembles a fish” — it has a coiled, fishlike form; and “its blood is used for dye” — its glandular secretion turns blue under sunlight. About 30 snails are required to dye a full set of tsitsit.
[⁵] Halakhic authorities:
– Rabbi Tsvi Hershel Schachter (b. 1941), leading Orthodox halakhic authority in the U.S., heads the Rabbi Isaac Elchanan Theological Seminary (Yeshiva University), author of Guinat Egoz (2007), which discusses tekhelet.
– Rabbi Zalman Nechemia Goldberg (1931–2020), former head of the rabbinical court in Jerusalem and director of the Talmudic Encyclopedia.
– Rabbi Shlomo Machpud (b. 1946), prominent Sephardic decisor of Yemenite origin, heads the Yoreh Deah kashrut agency in Bnei Brak, and actively advocates for reintroducing tekhelet as an authentic mitzvah.
[⁶] Accumulated evidence: Fragments of textiles dyed with tekhelet and argaman (crimson dye from Bolinus brandaris) have been found at Masada and in the Judean Desert. Chemical and spectroscopic analyses confirmed the use of Hexaplex trunculus as a dye source. Phoenician dye workshops have yielded thousands of broken shells. Pliny the Elder (Natural History, Book IX) names eight types of mollusks used for purple or blue dyes and details the manufacturing process.