Rediscovering folium to recreate historic blues and purples

April 22, 2020 9:15 PM

Turnsole became a mainstay of medieval manuscript illuminators starting with the development of the technique for extracting it in the thirteenth century, when it joined the vegetable-based woad and indigo in the illuminator's repertory. [Wikipedia] For the better part of the last century, however, the recipe for the vivid blue hue has been lost—until the publication of a new study in the journal Science Advances. While it was long known that Chrozophora tinctoria was the source of the ink’s sole ingredient, how folium was synthesized has eluded modern science. [Atlas Obscura]

Scientists Discover a New Compound in Medieval Ink That Was Once Lost to Time (MSN Science Alert)

Across the Mediterranean region, in fields and on roadsides, thrives a small plant with silvery leaves. It doesn't look like much, and in many cases it's an annoying weed. But in the Middle Ages, Chrozophora tinctoria was highly prized.

More from Wikipedia:

However, the queen of blue colorants was always the expensive lapis lazuli or its substitute azurite, ground to the finest powders. Turnsole was downgraded to a shading glaze and fell out of use in the illuminator's palette by the turn of the seventeenth century, with the easier availability of less fugitive mineral-derived blue pigments.

And more from Atlas Obscura:

(The plant is not named in old sources, but detailed descriptions of it helped chemists connect the dots.) Relying primarily on a 15th-century guide for making the paints for illuminating manuscripts, a team of Portuguese researchers set about to resurrect folium.
[...]
The old practices had been documented, but were laborious and time-consuming. Melo’s team consulted an exhaustive list of instructions from the 15th century—literally, The book on how to make all the colour paints for illuminating books. But it isn’t exactly a modern cookbook. The manuscript was written in Judeao-Portugeuse, the extinct language used by the Jews of medieval Portugal. Besides translation matters, there’s more than one way to skin a cat, and other sources provided different instructions—and none of them provided a known name for the fruit behind the hue. Luckily, Melo’s source offered a lot of clues.

The book on how to make all the colour paints for illuminating books: unravelling a Portuguese Hebrew illuminators’ manual (Heritage Science Journal)

We have been studying and reconstructing the medieval processes to make pigments and paints which were used to create medieval manuscript illuminations with the long-term goal of conserving them in the original artworks. The establishment of a dialogue between the medieval written sources and the multi-analytical molecular characterisation of the original colours has been our primary approach. This research has been carried out within an interdisciplinary team which includes conservators, chemists, and art historians.

Revista de História da Arte: Medieval Colours: between beauty and meaning, with more scholarly articles on these topics.

posted by filthy light thief (13 comments total)

it's such a good blue too. i feel like if i had a garden i would be making weird ancient dyes for no reason at all other than to confound the future archaeological record.
posted by poffin boffin at 11:19 PM on April 22, 2020 [7 favorites]

Yes, it looks like a really good pigment. If people had been able to make it into a fast dye it would have competed with indigo and might literally have changed history.
posted by Joe in Australia at 3:08 AM on April 23, 2020

_The book on how to make all the colour paints for illuminating books_

Now that is how to name a book.
posted by Glomar response at 4:54 AM on April 23, 2020 [1 favorite]

I guess it was a choice between taking a chance on bits of rocks brought from foreign lands at great expense, or mucking about at length with local plants and dodgy chemicals.

The only thing stopping me messing about with dyestuffs is the smell. Basically, if it doesn't ponk, it won't colour.
posted by scruss at 5:32 AM on April 23, 2020 [2 favorites]

Can someone who knows more than me post a link to an example of these vivid blues in manuscripts? I want to see it in its full glory. I love this stuff. Alchemy and magic at its finest.
posted by Silvery Fish at 5:53 AM on April 23, 2020

Finding an example online is made more difficult by the use of folium also to mean a page in a manuscript.

Here's the one image I could find.
posted by Emmy Noether at 8:52 AM on April 23, 2020 [9 favorites]

Silvery Fish, I found this chart linked on the Heritage Science Journal link above; you have to allow/manage cookies to get the site to work. Looks like katasol/turnsole is a deep blueish purple, as compared to the azul blue on that chart.
Years ago I stumbled across this book, Blue: The History Of A Color, by Michel Pastoreau. It was fascinating and I've regretted not adding it to my book hoard.
Thanks for this post, I'm diving into blue today.
posted by winesong at 8:57 AM on April 23, 2020 [1 favorite]

Very interesting stuff, but I found the Atlas Obscura article kinda frustrating. Aside from not showing examples of the dye (!!), it seemingly contradicts itself:

While it was long known that Chrozophora tinctoria was the source of the ink’s sole ingredient, how folium was synthesized has eluded modern science.

So it's long known that a plant whose name actually contains tinctoria was used in the dye. What's missing is the recipe to prepare it. But then this:

... none of them provided a known name for the fruit behind the hue. Luckily, Melo’s source offered a lot of clues.

“It says how the plant looks, how the fruits look … it’s very specific, also telling you when where the plant grows, when you can collect it,” says Paula Nabais, a conservation scientist at the New University of Lisbon, and the study’s lead author. “We were able to understand what we needed to do to collect the fruits in the field ourselves, and then prepare the extracts.”

What I think they're trying to say is, "Oh, this is the long lost recipe for that plant." Or maybe I should have read the article after my morning coffee.

Anyway, the Wikipedia article contains this delightful detail:

Textiles soaked in the dye vat would be left in a close damp cellar in an atmosphere produced by pans of urine. It was not realized that the oxidizing urine was producing ammonia, but the technique reminds us how foul-smelling was the dyer's art.

posted by sjswitzer at 10:21 AM on April 23, 2020 [2 favorites]

Folium? Hell it damn near killed 'im
posted by Fiasco da Gama at 4:40 PM on April 23, 2020 [1 favorite]

the technique reminds us how foul-smelling was the dyer's art.

Aged (ammoniacal) urine was also used by launderers and fullers of cloth. Basically everybody's clothes smelled of pee, all the time.
posted by Joe in Australia at 4:46 PM on April 23, 2020

Huh. Blue on The Blue.
posted by lhauser at 7:39 PM on April 23, 2020

Oh cool! I’ve been translating the Portuguese research papers on these studies for years, including these findings. I am so glad to see the team get the recognition they so richly deserve.
posted by msali at 8:46 PM on April 23, 2020 [7 favorites]

msali, please tell us more!
posted by filthy light thief at 9:49 PM on April 23, 2020 [1 favorite]