Tekhelet

Tekhelet (Hebrew תכלת) indicates a blue/indigo dye on several occasions describes in the Hebraic Bible, in particular during the construction of the Gate vault (Exode 25:4) and of the precription of the port of fringes to the corners of clothing (Nombres 15:38)

It was, according to the Talmud, extracted from a particular mollusc species, called 'hillazon (Chabbat 26a), which one finds only between Haïfa and Tyr, identified by the Talmud of Jerusalem to the will porphyra, and with the murex trunculus by the Rabbin Chaim Twerski
Cette species being unknown apart from this area, one could only calculate his true color. Rachi estimated that it was about a sunk nuance, reason for which the Tallit of the Ashkénaze S are striped of black, while Moïse Maïmonide leant for a light blue, reason for which Tallit Sépharade S are striped of blue. The Bible of the Rabbinate translated by azure.

Reference

site of an Israeli company which took again manufacture of it, in order to achieve in a perfect way halakhiquement regulation to place a bit of tekhelet in the tzitzit.

Random links:

_de_LÉ_Deirdre_(P20)