The Lost Blue Thread: The Mystery of Techelet and the Search for the Biblical Dye

In the Torah, we read detailed instructions about how the vessels of the Tabernacle were to be carried during Israel’s journeys in the wilderness. Each sacred vessel was carefully covered, out of reverence for its holiness.

Among these coverings, the Torah commands that certain items be wrapped in a “covering of techelet” — the mysterious blue-dyed fabric. Techelet was also used in the priestly garments and in various parts of the Tabernacle’s design. But there is another central mitzvah connected to techelet that applies to all generations: the blue thread of the tzitzit.

For centuries, however, Jews wore tzitzit made entirely of white threads, because techelet had disappeared.

The Disappearance of Techelet

The Midrash teaches that the techelet was hidden away. The Talmud describes its source as a rare sea creature — the “chilazon”, and offers clues about it: “Its body resembles the sea, its form resembles a fish, it comes up once in seventy years, and with its blood they dye tekhelet; therefore its dye is precious.”

Although the Sages of the Talmud were still familiar with this dye, its identity was eventually lost over the centuries, leaving no clear trace of how or from what it was produced.

The Radzyn Rebbe’s Quest

Over a hundred years ago, Rabbi Gershon Henoch Leiner, the Admor of Radzyn, launched a remarkable quest to rediscover techelet. A brilliant scholar and visionary, he traveled widely, consulting scientists and experimenting with marine creatures.

He eventually concluded that the “chilazon” was the cuttlefish (Sepia officinalis), known in Hebrew as “diynon harokchim” (the pharmacist’s squid), famous for the ink it releases for defense — and whose fluid was used in various medicinal preparations.

The Radzyn Rebbe believed that from this very ink, through proper processing, one could reproduce the ancient blue dye of techelet. He published his findings in a scholarly book, widely circulated among rabbis and communities, sparking intense debate.

However, most rabbis rejected his conclusion, arguing that the blue color resulted not from the cuttlefish itself but from chemical reactions in the dyeing process.

A New Candidate: The Murex Snail

In recent decades, a new and more accepted theory emerged — identifying the chilazon as the Murex trunculus, a Mediterranean sea snail also used in antiquity to produce Tyrian purple (argaman).

Archaeological discoveries have revealed ancient dye factories along Israel’s coast where these snails were processed, leading scholars to suggest that techelet too was derived from them.

This identification, however, remains controversial. Most halachic authorities still refrain from accepting it as definitive, though several prominent rabbis and Torah scholars have embraced it, and wear tzitzit with a thread dyed from the murex.

Waiting for Elijah

For now, the question of the true chilazon — the source of the biblical techelet, remains unresolved. Like many other sacred mysteries, it will likely be clarified only when Eliyahu HaNavi (Elijah the Prophet) comes to answer all remaining doubts.

Until then, the blue thread continues to symbolize something beyond the sea and the sky — a reminder of heaven itself, as the Talmud says: “Techelet resembles the sea, the sea resembles the sky, and the sky resembles the Throne of Glory.”