Rav Herzog investigated all the known sources regarding techeilet and the chilazon, looking for clues not only in halachic sources but in a vast array of secular sources as well. By that time, due to the work of the French zoologist Henri Lacaze-Duthiers, the German chemist Paul Friedlander, and a host of archeologists all along the Mediterranean, the scientific community was in agreement that murex snails were the source of the ancient dyes. Murex brandaris produced a red-purple dye – argamman – and Murex trunculus yielded a purple-blue dye – techeilet. Echoes of the Tiferet Yisrael ring through Rav Herzog’s conclusion that although all the evidence points towards the Murex trunculus snail as the Talmudic chilazon, if we assume that the true color of techeilet did not contain even a hint of violet, we must reject that snail as the source of the biblical blue dye.
The solution to Rav Herzog’s problem would not be found in his lifetime. In the 1970’s, however, two decades after Rav Herzog’s death, an Israeli chemist, Otto Elsner, discovered that at a certain stage in the dye process, if exposed to sunlight, the dye obtained from the Murex trunculus would in fact produce a magnificent sky-blue color that remained color-fast and stable. This discovery removed the difficulties that such rabbis as the Tiferet Yisrael, the Radzyner, and Rav Herzog had struggled with for over a century. It would take another 20 years until the mitzvah, lost for 1,300 years, would once again be fulfilled, as Rav Eliyahu Tevger produced the first techeilet strings with dye obtained from trunculus snails.
Although from a purely halachic standpoint the descriptions and requirements within the Talmud and other sources are vague and often contradictory, both Rav Herzog and the Radzyner – the two greatest experts on the laws pertaining to techeilet – agree on the minimum conditions that must be met in order to have “kosher” techeilet. Those are: (1) the dye must come from a sea-creature, (2) it must be fast and not fade or wash out, and (3) it must be the color of the sky. This list is based on the fact that the Talmud warns against using a fraudulent dye of vegetable origin known as kala ilan, which is indigo. This dye is sky-blue and is indistinguishable from real techeilet. Rav Herzog and the Radzyner argue that since the Talmud only warns against using this vegetable dye substitute, any marine animal that yields a fast, sky-blue dye must be suitable for the mitzvah of techeilet.
This seems to be an absolute endorsement of the trunculus dye, which meets all three criteria. However, one could argue that perhaps Chazal did not know of the trunculus snail, or maybe they were unaware of the process by which it could dye pure blue instead of violet. Three recent archeological discoveries prove that this was not the case. A saddlecloth unearthed in Siberia dating to the time of the destruction of the first Beit Hamikdash has a pattern of purple and a border of sky-blue – both of which have been absolutely identified chemically as coming from Mediterranean murex snails. A piece of cloth with a dark blue embroidery was found on Masada that dates back to the early Mishnaic period. It also was produced from murex dye.
Finally, tens of actual Murex trunculus shells were found in digs on Har Tzion in Jerusalem dating from the time of the second Temple, in a section believed to be the houses of kohanim. These finds prove conclusively that ancient dyers knew how to control the color of the murex dyes to produce sky-blue, that murex dyed wool was available in Israel in the times of the Tannaim, and that the Murex trunculus snail was well known in Jerusalem in the time of the Beit Hamikdash.
Within the halachic community today, there are three opinions regarding wearing techeilet from the murex. There are those who view the trunculus techeilet positively; many rabbanim wear it, many encourage their followers to do so, and some have ruled that one must wear it – to the point where there are even opinions that hold it is forbidden to wear white-only tzitzit. Other rabbanim remain unconvinced that the Murex trunculus is the true chilazon and counsel against wearing techeilet. Typically, these rabbanim argue that scientific, archeological, or historical proofs are not admissible in the court of halacha, and so the discussion must rely solely on authentic halachic material. A third school of thought admits that the Murex trunculus could indeed be the chilazon used in the times of the Talmud, but reject wearing techeilet nonetheless. They argue that once the chain of tradition with respect to a certain mitzvah has been broken, that mitzvah is lost to halacha – at least until Mashiach comes to reinstate it.