Tekhelet

Tekhelet (Hebrew: תְּכֵלֶת‎ təḵēleṯ; alternative spellings include tekheleth, t'chelet, techelet, and techeiles) is a highly valued dye described as either "skyblue" (Hebrew: תּכוֹל‎, Ta'ḵhol or Ta'chol, Ta'hol), or "light blue" (כחול בהיר‎, ḵa'chol bahir, ḵa'ḵhol bahir, ca'hol bahir), that held great significance in ancient Mediterranean civilizations. In the Hebrew Bible and Jewish tradition, tekhelet was used to color the clothing of the High Priest, the tapestries in the Tabernacle, and the tzitzit (fringes) attached to the corners of four-cornered garments, including the tallit. The mention of tekhelet is particularly notable in the third paragraph of the Shema, referencing Numbers 15:37–41.

The Bible does not specify the source or production method of tekhelet. According to later rabbinic literature, it was exclusively derived from a marine creature known as the Ḥillazon. However, the knowledge of tekhelet production was lost during the Middle Ages, leading to the omission of tekhelet from tzitzit. In recent times, many Jews believe that experts have identified the Ḥillazon and rediscovered the process for manufacturing tekhelet, leading to the revival of its use in tzitzit. The snail Hexaplex trunculus (historically known as Murex trunculus) is widely considered to be the creature responsible for producing authentic tekhelet.

A garment with tzitzit consists of four tassels, each containing four strings. There are three differing opinions in rabbinic literature regarding the number of strings that should be dyed with tekhelet: two strings, one string, or one-half string.