No more buckthorn berries left now in mid November for making the historic paint colour, Sap Green. I collected about four cups/ one litre of them a month ago and have been posting the results of my colour search here. Today I am wrapping up the basic buckthorn work and providing a review of what I have learned from my experiments.
Juicy blue-black buckthorn berries which the Field Botanists of Ontario tell me on FB that the birds eat only when desperate , so to go ahead – please make paint and ink with them!
The Rhamnus cathartica ( Common buckthorn) is a despised shrub here in Ontario and , as in many North American zones, is classed as invasive. I normally try to work with native plants to obtain dye colours. I find I am guided by pragmatism as much as by principle -native plants take less gardening work, survive extremes of neglect and weather more easily and attract interesting and useful critters. Why buckthorn, then? Because of its long and fascinating history as a dye plant as a species here and in other parts of the world.
For my research on the use of buckthorn for pigment, I have relied chiefly on the work of Dominique Cardon on natural dyes and of Daniel Thomspon on medieval painting. A delicious new book about making ink by Jason Logan rekindled my interest in buckthorn greens, and pointed me back to some of my previous work in similar areas, reported here: iris green ( also am historic colour) and walnut dyes/paints/inks. Enough background now. (Please check my references page and recent posts for full info).
Here is what you might do to get buckthorn (“Sap”) green. Believe me, there are a lot of recipes out there so no need to swear by mine- I don’t!
Here are two cups of ripe crushed berries in a one-litre/four cup slow cooker, heated to below boiling ( around 180) and cooked for an hour and a half or so, until the juice looks deep purple. My research turned up variations on whether to cook the berries or just squeeze the fresh uncooked juice. I tried both and found no difference in how the colour developed. Note also that to get a deep colour of green (a later step in the process), medieval recipes advised cooking down the liquid by at least half…so clearly, buckthorn is heat tolerant, which was my concern.
After the cooking step, time to strain the contents of the pot and then filter it. I used a wire colander for straining, then used a jelly bag for filtering the first time ( best to have more than one filtering session). I saved the residue for a second extraction as the old recipes advised.
After transferring the purple liquid into clean glass jars, time to shift the pH upwards in order to trigger the formation of that coveted green. Some of the old recipes suggest using a combo of alum and soda ash. I used alum acetate alone, about one teaspoon/5 ml per cup /250 ml canning jar- or until the colour turns dark green before your eyes! Stir the jar a bit, dissolve the alum in a tad of water, then add it. No need to be terribly exact. I figured if the alum did not work alone, I could throw in the soda ash, too. It worked fine!
I kept some purple liquid to use as is for its purple colour, then put aside a jarful of green liquid for further trickery. Natural dyers who are accustomed to working with modifiers such as ammonia, soda ash, iron, vinegar and copper sulphate will enjoy messing with the dye chemistry at this point. I did a little of that but my main goal was green and maybe a bit of yellow-green ( with soda ash as modifier)
Colour test strips
These colour trials are on 140lb watercolour paper – different colours will show on other papers. On fabrics? I have not tried the Sap Green on fabric yet but the ancient preference was to use silk for the easiest dye take up.
I have to say that my mopping-up cloth ( a heavy canvas) looks pretty colour receptive, even without a mordant:
The next step was to ” insissipate” the liquid – i.e., to concentrate its colour by either boiling it down to at least 50% of the original volume or by letting it evaporate to the same level. I boiled the dye down, having combined two batches of green dye liquid. ( Reminder: The berries can stand to be used for two extractions so do not chuck out the berries after the first straining. )
I filtered the boiled down liquid through three layers of cut up nylon pantyhose ( not thick ones) – in fact, I filtered the liquid also before boiling it down. You can filter as many times as you think the sludgey bits in the liquid need it.
The test strips here show the colours before and after filtering the green liquid. The darker green contains thickish cooked plant residue, the ligher colour is after filtering. Because Sap Green is a relatively transparent colour, you need to paint more than one layer for a deeper shade. The green sludge in the liquid might please your inner texture seeker, though.
As the photo shows, the green dye is now enrolled as an ink. To each one ounce bottle of liquid, I added 15 drops of gum arabic, one whole clove and for anti-mold overkill, one drop of very pungent tea tree oil ( used in soaps for Athlete’s Foot).
So I think that is it for buckthorn basics for now.
I have in mind to try a dye blanket with buckthorn green over plants in an ecoprint adventure. And there is one more medieval technique to try and that is to make a “clothlet” as reservoir to hold the green colour ( I will not be using a pig’s bladder as artists did way back) …I have made ” clothlets” for iris green ( reported on this blog). Thompson says Sap Green was also stored in clothlets. You know where I am going with this…
Next time: probably walnut ink! While I get my “clothlets” and dye carrier blankets sorted.