Sap Green and yellow from Buckthorn berries

Several important books talk about Sap Green, a medieval and renaissance pigment used in Book illumination among other things.  This year I had a mission to make some of this paint using the techniques and methods medieval paint makers may have utilized.

First I made note of all the different recipes for sap green and then had to find the materials these paint makers talk about.  

In De Arte Illuminandi, an anonymous 14th century treatise, translated from the Latin by Daniel Varney Thompson, Jr. and George Heard Hamilton in 1933, the author talks about several greens including buckthorn berries. (Thompson and Hamilton, pg 6-7)  

Buckthorn Berries are further described by the translators in their note "For the identification of these prugnameroli as buckthorn berries (Buckthorn = It. spincervino, spino gerbino), fruits of the varieties of buckthorn, Rhamnus, see Cennino ed. cit., II, p 32, n 1. (Thompson and Hamilton p 43). 

Further reading of this note explains the etymology of Sap Green which has nothing to do with the juice or sap from the plant and berries but how it may have been stored. 

"the color known in English as 'Sap Green,' the Italian verde di vescica (so called because the inspissated juice was preserved in bladders), the Saffgrien of Valentine Boltz, who specifies ed. cit., pg 75" the time of year "therefore, in Alsace, the color 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 these Rhamnus fruits was not entirely definite." De Arte Illuminandi pg. 29

So, Sap Green and yellow from the Buckthorn...

It took me what felt like forever to find Rhamnus spp. berries.  I searched the fields and ditches nearby, went to "Buckthorn Lane" in my local neighborhood in Saco, Maine; I found other trees with other fruits but no Buckthorn!  Finally someone said 'look for tall trees, usually somewhere wet' so I went back to my stomping grounds as a teenager in Wesbrook, Maine and found spindly trees in what used to be a protected wetland for turtles.  "This?!  Is this it?!" I begged my friends to confirm cell phone pictures of my find.  

The leaves look right from the plant books, the berries are dark and the bush was spindly and taller than I might have guessed, growing somewhere wet.  "Yes!", they chorused, "that looks right, try it!"

So I tried some of the recipes and will post them soon.  Sorry it's taken so long!