Wednesday, August 14, 2013

Purple Parchment and the Cave of Smoo

In the year 997, the excommunicated archbishop of Reims sent the Holy Roman Emperor a kingly gift: a copy of Boethius's On Arithmetic written in gold and silver inks on purple parchment. It had the desired effect. As I wrote in The Abacus and the Cross: The Story of the Pope Who Brought the Light of Science to the Dark Ages, my biography of that archbishop, the 17-year-old emperor summoned Gerbert of Aurillac to court with the plea, "Pray explain to us the book on arithmetic." Archbishop Gerbert became the emperor's tutor, friend, counselor--and ultimately, through the emperor's influence, Pope Sylvester II, the pope of the Year 1000.

Earlier in this blog, I described how parchment and ink were made in the Middle Ages. (See "How to Make a Medieval Book, Part I" and "How to Make a Medieval Book, Part II.")

But purple parchment? How did they color the parchment purple? I hadn't given that much thought.

Then the other day, researching something quite unrelated--the Viking settlements in northern Scotland--I stumbled upon the answer.

In 1992, a team of archaeologists led by Tony Pollard excavated four neighboring caves in a narrow inlet in Sutherland, one being the famous Smoo Cave. (See the great website, from which these photos of the cave were taken, at In 2005, Pollard posted their report online at

"Smoo" comes from the Old Norse word smuga, which Cleasby-Vigfusson, the classic Old Icelandic dictionary, defines as "a narrow cleft to creep through, a hole." The related verb is smjúga, "to creep through a hole" of which the past tense is smaug. Bells are now going off in the heads of all Tolkien readers--but I won't be following that digression any farther.

Back to Smoo Cave. Surprisingly, I had visited the cave in 1995. Two balding Scotsmen with rat tails and earrings took me on a river raft under a low stone arch, across a pool into which a sun-sparkled waterfall fell. In the dark cave, it was a real surprise. We disembarked in the dry inner reaches of the cave and had a geology lesson. The outer, larger cavern was made by the sea: the hole, wider at the bottom than the top, is a blowhole. The inner caverns were made by an underground river that feeds from a large lake. The waterfall only runs when there’s been rain—today’s fall is last night’s rain.

As Pollard points out, Smoo Cave has been a tourist attraction since at least the early 1700s. One practical-minded traveler described it as "stretching pretty far underground with a natural vault above." Inside, "there is room enough for 500 men to exercise their arms." (I'm imagining jumping jacks here--but maybe he means to practice their shooting?) There's "a harbor for big boats" at the cave's mouth, a pool full of trout, and "a spring of excellent water."

Earlier visitors also valued the cave for its usefulness--not its surprising bright waterfall. Pollard and his crew of archeologists found signs that Vikings had used Smoo Cave as a fishing camp, as well as a place to sit out a storm and repair a boat. They may have stopped here on their way from the Orkney Islands to Dublin. They butchered animals and cooked them. They ate dried fish they'd brought with them. They ground grain. They carved pins and knife handles and other useful objects out of antler and bone.

But the most interesting thing the Vikings did at Smoo and its neighboring caves was collect and crack open whelks. These were not just any whelks, but Nucella lapillus, also known as Purpura lapillus, the source since antiquity of a purple dye. These whelks are not edible, and they were not used as fish bait, Pollard says. "It is clear that purple dye was being extracted from the shells recovered from the cave."

The whelks, Pollard writes, "had been split from the second and third whorl and also split from the shoulder to the base.... This would have facilitated the removal of the animal from its shell to extract the ink."

In 1895, archaeologists found "Purpura-mounds" in Connemara, Ireland. The shells in the mounds had been broken exactly like those in Smoo Cave, though in Ireland there were many more of them. One heap measured 165 by 45 feet. In one square foot, the researchers counted two hundred whelks. Purpura-mounds have also been found in Cornwall, England, but Smoo Cave is the first record from Scotland, although the whelk is common there.

To learn how to make the dye known as Tyrean purple, Pollard refers the reader to the 1919 book, Shells as Evidence of the Migrations of Early Culture by J.W. Jackson. Like Pollard's own report, Jackson's book is available online. (Historical research is so easy these days!)

Jackson, in turn, cites the first-century Roman writer Pliny to explain that "the precious liquid was obtained from a transparent branching vessel behind the neck of the animal and that at first the material was of the colour and consistency of thick cream."

Several kinds of whelks produced purple dye. Small ones were smashed together in a mortar; if large, "the animal was taken out entire, usually by breaking a hole in the side of the shell, and the sac containing the colouring matter was taken out, either while the animal was still alive, or as soon as possible after death, as otherwise the quality of the dye was impaired." The sacs were salted, allowed to sit for three days, then boiled and frequently skimmed. Exposed to the sun, the fluid (smelling like garlic) slowly changed color, from creamy to yellow, green, blue, and finally a purplish red. After ten days, the dye was ready to use.

To dye wool, a clean fleece was dunked into the boiling dye pot and left to soak for five hours. It was taken out, cooled, and the wool plucked off and carded, only to be "thrown in again, until it had fully imbibed the colour" (still smelling like garlic--one reason the wearers of royal purple robes wore so much perfume, suggests Jackson). It took between one and two pounds of liquid dye to color a half-pound of yarn.

To turn parchment purple, Jackson says, the dye was used as a paint, applied with a brush. The "magnificent and expensive style of writing" on purple parchment with gold and silver inks was mostly confined to sacred texts. Jackson cites an English Bible and a Gospel book, another book of the Gospels commissioned by Louis the Pious, king of France from 814 to 840, and a Book of Prayers, "bound in ivory and studded with gems" owned by his son, King Charles the Bald.

It's significant that Gerbert of Aurillac, who would become "The Scientist Pope," owned a mathematical treatise made in this "magnificent" style. The book still exists in the Staatsbibliothek Bamberg in Germany, where it is catalogued as MS Bamberg Class. 5 (HJ.IV.12), but we don't know how it came into Gerbert's possession. Like the gem-studded prayer book, On Arithmetic was commissioned by King Charles the Bald in about 832. But the dedicatory verses apply equally to the young emperor Otto III as to King Charles, and scholars long thought Gerbert (known as a poet) had written them. Otto III may have thought so too, for he answered the gift with a verse.

Join me again next Wednesday at for another adventure in Iceland or the medieval world.

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