Sap Green (Part 2)

In Part 1 I described the discovery of Buckthorn growing in my small upstate New York garden, it's identification and subsequent production of berries. On September 4, 2013 I picked and sorted these berries into what you see below.

Buckthorn berries in three stages of ripeness; 28g of unripe green; 30g of medium-ripe blush; and 117g of ripe purple-black.

The period art manuals offer a variety of methods for creating the colour we know as sap-green, which all seem to be variations on squeezing the juice of the berries through a cloth, adding alum, sometimes ley and then storing it. This post will concentrate on the methods that DON'T use ley.

PADUAN MANUSCRIPT - Merrifield, 662
31. How pasta verde [sap green] is made. - Take the grains or berries of the buckthorn when they are quite ripe, and this will be about the end of September; let them soften for 7 or 8 days in a vase with water in which roche alum has been dissolved in the proportion of 1 ounce of alum to 6 of the berries, and boil it well until nearly half the water is consumed; then cool it, strain it through a linen cloth, put the part that is strained into pigs' bladders, and dry them in the sun or smoke; and this is called "pasta di vesicha."

Prep: Six individual ripe berries doesn't even register weight in grams ounces, therefore I am going to make the obvious leap that the above recipe means 1oz of alum to 6oz of berries. I do not have enough berries for that measurement therefore I am going to use 1oz (28.3g) of berries and divide that by six for the correct amount of alum, which is 4.67g.

The recipe doesn't specify an amount of water so I poured in an amount equal to approximately 2 inches in depth (yes, I should have measured), this will cover the berries by the same depth that they take up. Using a double-boiler setup I warmed the distilled water and alum in the glass jar just enough so that the alum completely dissolved, then removed it from the heat and allowed it to cool. This alum water gives me a ph3 (leaning towards ph4).

No mention is made about crushing or pounding the berries so I didn't. When pouring the berries into the water it immediately took on a green hue and it will be interesting to see how this deepens (if it does) over the course of the next week. All of the berries except a few are hanging out on the bottom of the jar, only a few are floating around on the top of the liquid or just under it's surface.

This was repeated with the green unripe berries, and then the semi-ripe blush berries using the methods described above. This time I measured and used 2oz of water to dissolve the alum in each jar. The unripe berries seem to float on the surface of the solution. The semi-ripe berries don't float like the green ones do, but they also aren't sat on the bottom of the jar like the fully ripe berries. On initial observation all three jars seem to be leeching the same green colour.

Result: A week later the individual jars are showing a strong dark colour, which upon close examination looks green to the eye but from a distance looks quite muddy. There is an obvious sediment in the bottom of each jar, but the berries appear plump and not to have started breaking down.

Opening the jars I noticed that they each seem to have vacuum-sealed themselves, but only a little. Once the lid was off, each jar gave me a slight smell of fermentation with the jar of ripe berries presenting more of a smell than the other two (I wonder if some sort of vinegar or wine can be made from Buckthorn berries?).

For the boiling portion of this recipe I again used a double-boiler setup. I didn't really achieve what I would call a rolling boil, but I did notice evaporation of some of the liquid. I have to admit that I got nervous during this portion of the recipe as I was worried about ruining what I do have. I may attempt the boiling portion again at another time.

For straining, I used a piece of natural linen placed in a small metal kitchen sieve which in turn was placed over a glass bowl. Taking the jar containing the ripe berries, I slowly poured the juice out over the linen so that it strained into the bowl beneath.

I then poured the berries that remained in the jar out onto the linen, gathered up the corners and crushed the sack in my fist to drain out any remaining juice. The berry refuse was then deposited in the rubbish bin. This is when I started to notice just how much sediment there actually was in the jar. The linen cloth was covered in it.

Next, I rinsed off my utensils and linen as I made a mental notation of just how much colour was rinsing out of them. Stupidly I didn't think about "clothlets"[1] until after I had drained the third jar. This is a subject I will need to look into for when I do this again.

One more note-to-self; wear gloves next time as the juice of Buckthorn berries stains your hands a wonderful green hue which is difficult to wash off. This is particularly evident in the absolutely stunning green that was achieved on the linen used to strained the juice from my jars.

The piece of linen used for straining the liquid from the jars, AFTER being rinsed and dried, sitting on it's original fabric.

I now have three jars of filtered juice from the ripe, semi-ripe and unripe berried of the Buckthorn. As you can see in the photograph below, they are two very distinct colours with a subtle difference between the jars containing the liquid produced from the unripe and semi-ripe berries. The next phase (and blog-post) will explore what these colours look like when painted as swatches.

The three differing colours obtained from (left to right) ripe, semi-ripe and unripe Buckthorn berries.

BOLOGNESE MANUSCRIPT - Merrifield, 420
89. To make a good green with buckthorn. - Take small berries of buckthorn when quite ripe, put them into a glass vase, and crush them well with your hands; then place them in the sun, and let them remain until the juice rises above the berries; then strain the refuse, and throw it away, and if the juice weighs one pound put into it the weight of two quattrini [2] of roche alum in powder. Place the mixture in the sun in a well-closed glass vase, and let it stand three or four days, stirring it well three or four times every day; and if it should happen to dry after a time, distemper it with clear ley, with a little gum.

Prep and Results: I found this recipe to be a little strange. Crushing the berries as described in the first sentence produced hardly any juice. What little juice there was then evaporated over the course of the following couple of days.

As a variation, I tried this same recipe and added a little distilled water to assist in making a juice. This worked slightly better but produced no where near "one pound" of juice. As a result, I didn't really get a chance to properly follow through with this recipe.

The juice didn't really "rise above the berries" and I'm curious to know if this is just a result of the batch-size I was using. The recipe does mention "one pound" of juice which leads me to believe that they were processing HUGE batches at a time.

Nevertheless, I squeezed out what I could into a clean glass jar and quickly realized that continuing to follow this recipe with what I had was pointless.

I poured what little juice I had out into an oyster shell, it is almost the colour of red wine. Adding alum to the juice made it turn an olive purple, so I added more until what I had in my shell was a definitely green liquid. Whats funny is that even though I see a definite green hue with my eyes, all the camera see's are red hues.

Juice of the ripe Buckthorn berries in an oyster shell with added alum. Although the photograph displays the liquid
as the colour similar to red wine, to the human eye it is actually green.

From Thompson, 170
To prepare the green, the juice of the ripe buckthorn berries was squeezed out, mixed with a little alum, and allowed to thicken by evaporation. The result was a gummy green colour, generally rather olive, transparent, and rich. The use of buckthorn berries was used quite early, without preparation, to temper and enrich verdigris; and probably it's use as an independent pigment came about as a development of its accessory function. Used by itself, without alum, the juice is somewhat yellow or green, according to the ripeness of the berries, but it's colour is very fugitive. . .The colour made with alum is more durable, though not permanent . . . 

Prep: 20g of the ripe purple berries we deposited in a 6oz mason jar and crushed,  I then covered them with purchased distilled water of ph8 to the 2oz line. The reason I added a little water is so that I can soak out the juice (and hopefully more colour) from the berries, as when crushing the berries they didn't seem to produce much liquid. I do plan on letting this verjuice sit for a week before straining it as many of the other recipes suggest. Looks like the basic verjuice is ph5. It has a very muddy colour which could be called olive brown, with a hint of green.

Results: After a week in a sealed mason jar the berries look and smell like they've fermented. I used a piece of natural linen to strain the mixture and squeeze the berries of liquid, my result is a liquid almost the same  colour as red wine. Strangely, the linen cloth has a slight green tint to it.

I added a generous amount of alum to the purple-juice and it immediately turned into a dark green. I didn't really measure but it was six scoops with the plastic spatula. I basically added alum until I had a Rich green colour. After a number of days had passed the juice had returned to a muddy brown colour, suggesting that something other than alum affects the colour. [3]

Conclusion:

These recipes seem like overkill. I feel like all I really need to do to obtain the colour is to squeeze the berries through linen into a shell and add a little alum. I will be curious to see how these different methods paint up when used in swatches. There is also the use of lye in some of the recipes which needs to still be explored.

Footnotes:

[1] From the British Library's Catalogue of Iluminated Manuscripts glossary: "A piece of cloth impregnated with PIGMENT (generally a vegetable dye). A portion of such cloth, when soaked in a little BINDING MEDIUM, releases its colorant and produces an artist's pigment. Clothlets are called petiae in Latin and pezze or pezzette in Italian; bisetus folii refers to clothlets dyed with folium, or turnsole, extract. Clothlets were a convenient way of carrying or shipping vegetal pigments, and they were especially popular from the fourteenth century on, with the growth of the textile trade. Glazes of vegetable dyes were often used to enhance other colours in book ILLUMINATION, since they created a rich, glowing, and transparent effect."

[2] Since I had intended to follow this recipe I needed to figure out what a "quattrini" was and how much it weighed. Merrifields footnotes on page 420 tells us "Quattrini. Small copper con, worth about the fifth part of a crazia, or the 60th part of a Florentine lira; perhaps so called because a quattrino was of the value of four denari or piccioli, now no longer in use." With a little searching, I discovered a 15 c. quattrino from Bologna that was listed as weighing 0.39 grams (and of course now I can't find the screenshot I saved for reference).

[3] Later discussion with Master RanthulfR of the Midrealm regarding the colour of the liquid suggests that the calcium carbonate in the shell reacts with the liquid to turn and keep it green. Further observations are needed by myself, but this information corresponds with what I'm currently seeing in my own tests.

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

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