Tekhelet

Tekhelet (Hebrew: תְּכֵלֶת təḵēleṯ) is a blue dye that historically held great significance in ancient Mediterranean civilizations. It is mentioned in the Hebrew Bible and is accordingly commonplace in Jewish culture, wherein it features prominently to color the fringes (called tzitzit) of several Jewish religious garments, such as the tallit. The dye was similarly used in the clothing of the High Priest of Israel and in tapestries in the Tabernacle.

Biblical texts do not specify the source or production method of tekhelet. Rabbinic literature, however, records that it was produced from a marine animal: ḥillāzon (חלזון). The practical knowledge of tekhelet production was lost over time, resulting in the omission of the dye from tzitzit. The ḥillāzon has been identified in contemporary times as Hexaplex trunculus.

Of the 49 or 48 uses of the word tekhelet in the Masoretic Text, only one refers to fringes on cornered garments of the whole people of Israel (Numbers 15:37–41). Six are non-ritual uses, such as Mordechai dressing himself in tekhelet before the King of Persia (Esther 8:15). Tekhelet could be used in combination with other colors as in 2 Chronicles 3:14 where the veil of Solomon's Temple is made of tekhelet, Tyrian purple (Hebrew: אַרְגָּמָן, romanized: ʾargāmān) and scarlet (Hebrew: שָׁנִי, romanized: šāni or כַּרְמִיל karmil). Ezekiel 27:7 mentions that tekhelet-cloth could be obtained from "isles of Elishah" (Cyprus). All Biblical mentions of tekhelet imply that it was difficult to obtain and expensive, an impression corroborated by later rabbinic writings.

The manufacture of tekhelet is believed to date back to 1750 BCE at least. In the Amarna letters (14th century BCE) tekhelet garments are listed as a precious good used for a royal dowry.

Data about the dye seems to have been lost sometime after the period of Rav Ahai (5th–6th century). The Tanhuma (8th century) is the first written source to lament this loss.

In his doctoral thesis (London, 1913) on the subject, Yitzhak HaLevi Herzog proposes H. trunculus (then known as Murex trunculus) as the most likely candidate for the source of the dye. Though H. trunculus fulfilled many of the Talmudic criteria, Herzog's inability to consistently obtain blue dye from the snail precluded him from declaring it to be the dye source.

In the 1980s, Otto Elsner, a chemist from the Shenkar College of Fibers in Israel, discovered that if a solution of the dye was exposed to ultraviolet rays such as from sunlight, blue instead of purple was consistently produced. Elsner's discovery of that exposure to sunlight turns the red 6,6'-dibromoindigo extracted from the hypobranchial gland of H. trunculus snails into a mixture of blue indigo dye and blue-purple 6-bromoindigo was widely viewed as resolving Herzog's issue.

In 1988, Rabbi Eliyahu Tavger dyed tekhelet from H. trunculus for the commandment of tzitzit for the first time in recent history. Based on this work, four years later, the ''Ptil Tekhelet'' Organization ^[he] was founded to educate about the dye production process and to make the dye available for all who desire to use it.