Photo by Eugene Weisberg, Tel Aviv

A piece of white wool changes almost magically to blue after being dunked in a yellow chemical solution. The same dye solution was used in biblical times to color the curtain of the Temple, the covering of the desert Tabernacle and the rich robes of kings and priests. In the Torah, God instructs his people to “make for themselves fringes on the corners of their garments [and] attach a cord of blue (tekhelet) to the fringe at each corner” (Numbers 15:37) as a reminder to keep his other commandments. Wearing these fringes, or tzitzit, is a mitzvah (commandment) that observant Jews, including author Ari Greenspan, have always striven to obey.

But the chemical makeup of the biblical blue dye was a mystery until just a few years ago. In the accompanying article, Greenspan recounts how the modern world recovered biblical blue. The source: the unassuming Murex snail shown to the right of the beaker in this photo.