Friday, September 6, 2013

Sap Green from Buckthorn Berries (Part 1)

Given the amount of words written about sap green it's not surprising that it was a valued pigment within the illuminators pallette. Made from the berries of the buckthorn (Rhamnus), it was used not only as a "verjuice" to enhance the colour of verdigris, but also later as a colour in it's own right which the Italians apparently called verde di vescica since it was kept as a thickened liquid in "bladders".

So, what is Buckthorn?
Buckthorn found growing in my garden.
Rhamnus is a genus of about 150 species of shrubs or small trees, commonly known as buckthorns, which bear fruits of dark blue berries. They are common to North America and Asia but also appear in Europe and North Africa.

Who really knows which species the medieval recipes used, all we can really do is speculate on the ones that could have been available. Some possibilities include [1]:
  • Rhamnus alaternus - Known as Italian Buckthorn or Mediterranean Buckthorn.
  • Rhamnus cathartica - Known as Common Buckthorn or Purging Buckthorn. Native to Europe including the British Isles. This species is mentioned in Merrifield as being used by the Italians (ccxviii).
  • Rhamnus lycioides - Known as Black Hawthorn, European Buckthorn, Mediterranean Buckthorn. Native to the Mediterranean region of southern Europe.
  • Rhamnus frangula - Known as Alder Buckthorn. Native to Europe, including the British Isles. "The bark yields a yellow dye, and the unripe berries furnish a green dye."
  • Rhamnus glandulosa - Found in Portugal and Spain.
Thompson tells us in The Materials and Techniques of Medieval Painting that ". . . it is evident, from experiments which have been made in the laboratory of the Coultauld Institute, that some varieties yield inferior colours. . ." (170). My guess, they would have used whatever was available to them locally and the colour may have differed according to locality, some more so than others.

Harvesting the berries.
The berries of the buckthorn are small and globular, up to about 10mm in diameter. They seem to form in non-uniform cluster along the growing branch. 

In the footnotes of De Arte Illuminandi translated by Thompson and Hamilton we are told that ". . . the colour came out yellow if the berries were gathered in August, and green if they were gathered about the middle of September, we may probably assume that the quality of green yielded by the Rhamnus fruits was not entirely definite. It must have varied in its content of yellow, according to date and the nature of the season. . . "(43). Which sounds like it ties in with the experiments made by the Coultaud Institute mentioned by Thompson in the quote above.

Freshly collected Buckthorn berries in a metal bowl.
Since discovering Buckthorn growing in my north American garden early this spring I've been waiting patiently all summer for the berries to develop and ripen. From my reading I knew that this would likely happen around the end of August or into September, and so I've been keeping a watchful eye.

On Sept. 4th I picked 175 grams of berries ranging in colour from mostly green to very deep purple, almost black. I didn't concern myself with the ripeness while picking as I knew that I would be separating them to see what the difference in colour will be once processed. They were then separated into three rough colour groupings and deposited into glass mason jars, of which; 28g was of mostly green (unripe) berries that according to sources should produce a very yellow colour; 30g of "blush" berries (obviously purple but still showing green) that fall somewhere between unripe and ripe; and finally 117g of squishy, ripe, deep purple-black berries which should yield the sap green pigment described.

Fresh Buckthorn berries divided by ripeness and contained in clean, glass Mason jars.
As an aside, when I put water in the used metal collection container to wash it, the water turned a yellow'ish-green colour. The only thing left in the container was a clear sticky substance left from the berries.

My next step will be to follow some of the recipes found within various treatises to produced the sap green colour used by period artists.

Continued in Part 2

Footnotes
[1] The footnote on pages 32 and 33 of the Thompson translation on Ceninni's Il Libro dell' Arte mentions both R. alaternus and R. catharticus but also offers further suggestions for potential species of Rhamnus available to medieval artists.

Cited Works & Bibliography
ANONYMUS. De Arte Illuminandi: The Tecnique of Manuscript Illumination. Translated by Daniel V. Thompson and George H. Hamilton. New Haven: Yale University Press., 1933. Facsimile.

CENNINI, Cennino D' Andrea. The Craftsman's Handbook. The Italian "Il Libro dell' Arte."Translated by Daniel V. Thompson, Jr. Mineola: Dover Publications, Inc., 1933. Print. ISBN 13:978-0-486-20054-5

DOUMA, Michael, curator. Pigments through the Ages. 2008. Institute for Dynamic Educational Development. Web. 28 August 2012. < http://www.webexhibits.org/pigments >

MERRIFIELD, Mary P. Medieval and Renaissance Treatises on the Arts of Painting. Mineola: Dover Publications, Inc., 1999. Print. ISBN 0-486-40440-4

Rhamnus (genus). 2013. Wikipedia. Web. July 3, 2013 < http://en.wikipedia.org/wiki/Rhamnus_(genus) >

THEOPHILUS. On Divers Arts. The Foremost Medieval Treatise on Painting, Glassmaking and Metawork. Translated by John G. Hawthorne and Cyril Stanley Smith. Mineola: Dover Publications, Inc., 1979. Print. ISBN 0-486-23784-2

THOMPSON, Daniel V. The Materials and Techniques of Medieval Painting. Mineola: Dover Publications, Inc., 1956. Print. ISBN 0-486-20327-1