As a graduate student, I heard a fascinating lecture by Nobel-prize-winning chemist Roald Hoffmann on his “side project,” a chemical/historical exploration of indigo dye. Indigo is the chemical responsible for the color of blue jeans — mostly made synthetically today, but naturally found in certain plants (indigo and woad) and certain Mediterranean snails.
From these snails, ancient Mediterranean peoples derived the famous Tyrian purple dye, the “royal purple” that only Roman emperors were allowed to wear. The dye’s exact color could vary from dark red to purple to blue — and this blue was (quite literally) intertwined with the ritual traditions of ancient Judaism.
Hoffmann, a Polish Jew who escaped the Nazis as a child, described the significance of this blue dye, known as tekhelet, in his own Jewish heritage. References to tekhelet abound in the Hebrew Bible, particularly in descriptions of worship in the tabernacle or Temple, where the Lord commands that “blue and purple and scarlet stuff” be used for priestly robes and coverings for the sacred objects.
In the Book of Numbers (15:39-40), the Lord further commands:
“They shall make for themselves fringes on the corners of their garments … and they shall place upon the fringes a cord of tekhelet. So, when you see the fringes, you shall remember all of the commandments of the Lord and do them.”
These fringes, called tzitzit, are worn by Jewish men as a perpetual reminder of their covenant with the Lord. The blue color symbolized the glory of God, evoking the expanse of the sky and the waters of his creation.
Hoffmann explained that later rabbinic traditions specified that tekhelet could only be considered authentic if produced from snails, not from plants — no cheap substitution would do for this sacred reminder. However, around the 6th or 7th century AD, the technology for creating tekhelet from snails was lost. Blue dye was still produced from plants or, later, through synthetic chemistry, but true tekhelet was nonexistent. In many Jewish communities, tzitzit were made pure white from then on — the absence of the blue becoming yet another symbol of loss for the Jewish people, and of longing for the coming of the Messiah who would restore the kingdom, the temple and the covenant.
Hoffmann then described his research to reconstruct the ancient chemical process for creating tekhelet dye from snails. First, the snails would be harvested — 10,000 of them to produce just one gram of dye! This gives an idea of just how precious this color was, valued by ancient peoples higher than its weight in gold.
To make the dye colorfast, the extract would go through a laborious process of boiling, fermentation and treatment with other (nasty) substances. In the second-to-last step of this process, the dye would lose its color, turning a sickly yellow. Only upon dipping cloth in the mixture and exposing it to air and sunlight would the indigo color reappear. As Hoffmann put it, believing that this dye would give you back the beautiful color you had worked so hard for was as much an act of faith as of chemistry.
I remember so distinctly Roald Hoffmann’s lecture about indigo, not only for the fascinating history and chemistry, but also for the deeply personal meaning the project clearly had for him.
Matter matters, as we chemists are fond of saying. The material, the substance, the “stuff” of our lives is infused not just with scientific, but spiritual meaning. God speaks to us through matter, through color, through craft, through beauty, through sacrament.
For us as Catholics, this should come as no surprise. For us, whose God has become flesh, matter has been made even more sacred. Our Messiah has indeed come to touch and to heal us — by “even the fringe of his garment”.
Anna Christianson is an associate professor of chemistry at Bellarmine University. She thanks Rabbi Matt Derrenbacher for helpful edits of this column.
