Tekhelet is a blue dye mentioned 49 times in the Hebrew Bible/Tanakh. It was used in the clothing of the High Priest, the tapestries in the Tabernacle, and the tassels (Hebrew: ציצית, Tzitzit (or Ṣiṣiyot) [tsiˈtsit], pl. Tzitziyot or Ṣiṣiyot) affixed to the corners of one’s four-cornered garment, such as the Tallit (garment worn during prayer, usually).
In the Septuagint, tekhelet was translated into Greek as hyakinthos (ὑακίνθος, “hyacinth”).
According to the Talmud, the dye of Tekhelet was produced from a marine creature known as the Ḥillazon (also spelled Chilazon). According to the Tosefta(Men. 9:6), the Ḥillazon is the exclusive source of the dye.
- In 1858, a French zoologist found that there were three Mediterranean mollusks that produced purple-blue dyes. One, called Murex Trunculus, a kind of snail, was the one many people thought was the source of the blue used for the tekhelet.
- Rabbi Gershon Henoch Leiner, who also lived in the 1800s, independently started an expedition to find the Hilazon. Hilazon is the word the Mishna uses to describe the animal that produces the blue dye. Rabbi Leiner found a certain squid he thought was the Hilazon. He brought the squid to an Italian chemist for help in making the dye. They were successful and Rabbi Leiner and his followers started wearing the squid tekhelet.
- In 1913, the Chief Rabbi of Ireland wrote a paper on porphyrology – the study of purple. When he sent samples of Rabbi Leiner’s squid tekhelet to chemists for testing, the chemists found that the dye was inorganic, so it was not purely a squid product.
- It turns out the color was a synthetically manufactured color called Prussian blue. The Chief Rabbi refused to believe that Rabbi Leiner would purposely mislead his students, so he decided to study the process used to create the dye. He discovered why the dye was inorganic. The process of creating the dye involved heating the squid ink to a very high temperature and then adding colorless iron filings. This produced the blue color. We now know that almost any organic substance put through this process would produce blue dye! Unfortunately, it seems that the Italian chemist had misled Rabbi Liener and the dye was colored by the chemical reaction with the iron filings, it was not entirely natural.
- Now, back to the French zoologist’s Murex Trunculus, the snail. There were two problems with this creature that seemed to disqualify it from being the Hilazon described in the Mishna. First, it did not look like the ocean, which is what the Mishna specifies. Instead, its shell was white with brown stripes. This problem was solved when people found that when this snail was in the water it covered itself with a slime that made it look the color of the sea so that requirement was fulfilled.
- Second, its dye was more purple than blue. This problem was recently solved when someone noticed that the snail’s dye turned more bluish in sunlight. If the dye is exposed to sunlight at a certain point in the manufacturing process, the dye will turn out a brilliant blue.