In the famous Greek myth, the hero Jason and his band of Argonauts seek a precious fleece, allegedly woven from the wool of a golden ram, to exchange for the throne of Thessaly. Around the same era, stories told of the biblical King Solomon describe him wearing a lightweight tunic that shimmered when he stepped into the sunlight. The New Testament repeatedly describes angels as being clothed in "pure and shining linen,” and the apostle Luke as wearing “shining garments.” But was this all just metaphorical holy light—or something real and reproducible? 

As far as anyone knows, there's never been a sheep whose wool gleamed golden. However, many theories have been concocted to explain the existence of a sparkling gold fabric long before the invention of lamé. It’s just a symbol, most say—of wealth, kingship, authority, and so on. 

But these stories also share a possible interpretation that’s based in reality: They may be referring to byssus.

Also known as sea silk, byssus is an ancient textile woven from the beard of various clams, and which appears dark brown until placed under direct light, when it glitters like gold. Although it can be made from a few different mollusks, the beard of the noble pen shell, Pinna nobilis, has historically been the preferred source. Pen shells are quite large as clams go, growing up to 4 feet in length, and produce thin but very strong filaments—solidified saliva, really—that anchor the mollusks to the floor of the sea. With strands about half the circumference of a human hair, the silken beard of P. nobilis is ideal for weaving, as it's far less coarse than that of its cousins in the pinnidae family. 

The threads of the fabric’s history are difficult to trace, beginning with the fact that the word byssus itself once referred to any precious textile. The Old Testament reportedly includes 45 mentions, but some of them, judging from the context, almost certainly refer to linen, cotton, or regular silk. The same is true for the cloth that Egyptians used to wrap mummies, which scholars have translated as “byssus." But it’s hard to be sure which byssus they’re talking about: sea silk, or another precious textile? The silken filaments that compose the pen shell’s beard are also called byssus, adding to the confusion.

And fictions have thrived around byssus: In 945, the Book of Tang (Tángshū), a historical work about the imperial Tang dynasty of China, described a golden textile called byssus as being woven “from the hair of the sea-sheep,” whatever that might have been. Estakhri, a 9th-century Persian geographer, writes similarly of an animal that runs into the sea and rubs itself against certain stones, whereupon it produces "a kind of wool of silken hue and golden color."

Much later, Jules Verne spoke of it in Twenty Thousand Leagues Under the Sea. In the original French version, he describes the crew of the Nautilus being dressed in byssus and detailed its aquatic origins. However, “byssus” was called “seashell tissue" or "fan mussel fabric" in English translations, which caused some readers to believe the material was dreamt up expressly for science fiction. 

The real, clam-made byssus was highly prized by the ancient Greeks and Mesopotamians, among other cultures, for not only its glittery, color-shifting properties but also for its combination of daintiness and warmth. Stockings and gloves were popular uses for sea silk; a pair of byssus gloves were reported to be so extraordinarily light they would fit folded inside of a walnut's shell, and a pair of stockings inside a snuff box. 

Women spinning bysso, from a display in Sardinia. Image credit: Sicco2007, Flickr // CC BY-NC-ND 2.0

Byssus fell out of fashion for a few centuries, although it enjoyed a short renaissance in the 1800s among the wealthy. But aside from museum and gallery collections exhibiting vintage pieces, it’s nearly nonexistent today, and for good reason. P. nobilis is currently endangered—a victim of not just overfishing and trawling in the Mediterranean but also of pollution, to which it's highly susceptible. These factors make the harvesting of the byssus all the more difficult—and the cloth itself perhaps even more expensive than it was in ancient times.

However, Italian weaver Chiara Vigo, who says she has developed a method of harvesting the silken fibers from the pen shell without killing the creature, has been granted special clearance to dive for them in her hometown of Sant'Antioco, Sardinia, while accompanied by members of the Italian Coast Guard. Vigo’s family has been weaving byssus for centuries. She learned the trade from her grandmother—although it should perhaps be called a “trade” only loosely, since she's sworn to never sell the cloth (further adding to its scarcity). Vigo believes the cloth is sacred, calling it “the soul of the sea,” and claims to have never earned a cent (or lira) from her skill.

As the BBC notes, Vigo also believes that a gift of byssus brings good fortune to families, so she provides her service to those who appear at her studio in person. She gives byssus-embroidered christening dresses to babies, byssus bracelets to pregnant women (or those who aspire to be), and byssus rings to little girls (to bring back to Vigo when they're grown and engaged, whereupon she’ll make them a byssus doily for their marriage bed).

Rumor has it that a few elderly women on the Italian mainland still know how to weave byssus, but Vigo is the only known living master. She’s only person who can make it shine, using a special solution, and who can dye it in the traditional way. She’s also said to be the only person who is legally cleared to harvest it. And Vigo holds a secret, to boot: She’s one of the few living people who know where exactly the field of pen shells is located in the waters surrounding Sant’Antioco.

Whatever the truth behind byssus’s complicated backstory, the good news is that for now, sea silk is still quietly being woven in an ancient village on a tiny island just off of a larger island in the Mediterranean—and that Chiara Vigo is willing to share her knowledge. In addition to spending a few hours in the evenings teaching students how to weave byssus, she has also taught her daughter the craft, vowing that she’ll one day take over the family tradition. Hopefully, in an era where glitter is everywhere but traditional materials are scarce, the fabric will continue to survive, and as more than a myth.