Joel Guberman has a colorful story - but it's all in hues of royal purple and brilliant blue. From a nondescript building in an industrial zone in the Judean Desert east of Jerusalem, the New Jersey-born occupational therapist is engaged in a halachic revolution - getting Jews to adopt the lost commandment of wearing of blue tzitziot (ritual fringes). Guberman is an expert on techelet - the little-understood dye referred to 48 times in the Bible that colored the tassels of Jews' prayer shawls. Long before Diaspora Jews began to specialize in the shmatta business, they had a historic connection to dyeing textiles, he explains. One of the Torah's 613 commandments is to incorporate an azure thread among the tzitzit as a conspicuous reminder of the complete system of divine rules. That single blue thread and three white ones are folded so as to appear as eight strings in each of the four corners of both the tallit and the arba kanfot undergarment. Guberman explains that the famous medieval commentator Rashi interpreted the word "tzitzit" as having the numerical value of 600. Together with eight threads of each tassel and the five sets of knots, the sum totals 613. Archeological remains of dyeing vat complexes and vast mounds of snail shells found along the Mediterranean coast from Dor south of Haifa to Tyre attest to the lucrative ancient technology of techelet. A rare species of sea snail generated huge wealth for the ancient peoples of Judea and Phoenicia - today's Israel and Lebanon. Eager to control this source of revenue, the Roman Empire restricted the wearing of royal purple and techelet blue to aristocracy and made the manufacture of these dyes a monopoly of imperial dye houses. The laws drove the Jewish techelet industry underground, just as other restrictive policies encouraged the Jews to emigrate into exile. By the time of the Arab conquest of the Land of Israel in 638 CE, the technology had been lost. As a result, Jews began wearing plain white tzitziot. Now that is changing, thanks to the efforts of Ptil Tekhelet (the Association for the Promotion and Distribution of Tekhelet), which Guberman co-founded in 1993 together with scuba divers Dr. Ari Greenspan and Baruch Sterman, who holds a PhD in physics, and Rabbi Eliyahu Tavger. Their nonprofit foundation is based on the 1980s research of Otto Elsner, a chemist at Ramat Gan's Shenkar College of Engineering and Design, who discovered that if a solution of the purple dye made from the hypobranchial gland of the Murex trunculus snail was exposed to the sun's ultraviolet rays, it would turn a deep shade of blue. Popularizing that knowledge has been a slow process. According to the Talmud, techelet is a specific azure dye produced from a sea creature known as a hilazon. Rabbinic sages ruled that vegetable indigo dyes were unacceptable. Over the past 150 years, several marine creatures were proposed for reviving the biblical process of dyeing the tassels, among them one favored by Israel's first chief rabbi, Isaac Herzog, father of sixth president Chaim Herzog. He believed that the violet pelagic snail, Janthina janthina, was the source of the ritual techelet. Another theory was proposed by Rabbi Gershon Hanoch Leiner, known as the Radzyner Rebbe, who produced blue dye from the black ink of the Sepia officinalis (the common cuttlefish). But chemical analysis identified his dye as Prussian blue, an inorganic synthetic color derived from iron filings and not from the squid itself. That dispute continues to reverberate until today. Most of the blue-colored tzitziot worn in Israel today are dyed from the inexpensive cuttlefish, Guberman acknowledges. (The techelet factory in Radzyn near Lublin in Poland was destroyed during the Holocaust, and the lost technology was revived in Israel following 1948, thanks to the pre-war research of Rabbi Herzog.) How mainstream is the wearing of techelet? "It's definitely becoming more and more popular," observes Rabbi Avi Berman, director-general of the Orthodox Union in Jerusalem. "Everyone is hoping one day we will know for sure what the right techelet is so we can fulfill the biblical commandment." Berman himself does not wear techelet, following the ruling of former Sephardi chief rabbi Mordechai Eliahu that, pending the coming of the Messiah, there cannot be complete certainty of which sea creature constitutes the hilazon. While rabbis tend to be tradition-bound and reluctant to adopt change, techelet has become popular among nationalist youth and those living in Judea and Samaria, notes Guberman. "We believe it is a process how Halacha gets accepted," he says. "Nowhere in the Torah does it say that the techelet [source] was a mollusk. But nowhere in the Torah does it say gold is a metal. It's a given." Today the Ptil Tekhelet foundation is selling some 500 to 800 sets of tzitziot monthly. The process requires more than a ton annually of Murex trunculus, most of which Guberman imports from Croatia, Tunisia, Greece and Spain. The fringes sell for between NIS 80 and NIS 190, depending on the length and thickness of the string. They are spun on site using merino sheep wool. "We're the only place in the world that does this from the Murex trunculus," Guberman notes with pride. What of the future? Ptil Tekhelet has consulted with Israeli marine biologists and is looking for an investor to establish a snail-breeding facility in Michmoret or Eilat. When that happens, Israel will have a new , albeit non-kosher, export delicacy - escargot de mer.