OMG It's Nature: Walnut Ink, Locally Produced and Manufactured

I’m being used by a Southern California Black Walnut (Juglans californica[1]). I don’t particularly mind since I’m using the walnut tree, too. Our relationship is based on me taking its babies (i.e., seeds) and giving them a safe place to sprout—more on that later. In exchange, I get walnut husks full of juglone, rendered below.

Juglone, the molecule, in its oxidized form. Gray atoms are carbon, red are oxygen, and hydrogens aren't shown to make for a clearer picture. Making this made me miss chem class[2]. Don't you dare judge me!

Juglone is a rather useful chemical; walnuts manufacture it to kill their neighbors. Indeed, a host of plants from birches to chrysanthemums to tomatoes are sensitive to the juglone that may leach from walnut roots, leaves, or fruits. When planted beneath a walnut, these vulnerable species wither and waste away. There’s no need to share precious water and nutrients when a tree kills its neighbors. Reducing competition—it’s the wisdom of the walnut and the reason for juglone.

Us humans, however, have found many uses for juglone never anticipated by the tree that makes it. When it oxidizes, juglone turns a deep brown. Juglone based inks/dyes are permanent and lightfast, so they are great for hair dye and food coloring[3]. It was even used to embellish the margins of bibles when the good book was handwritten. And that’s what I use juglone for--ink.

Southern California Black Walnut, our local species, excretes less juglone than the walnut trees native to the eastern United States. However, the husks (the green, fleshy tissue that surrounds what is commonly called an unshelled walnut) do produce the chemical in fair concentrations. As proof, you’ll find that if you rip through the husk to reach the walnut inside, your hands will be stained brown for days. I find this a small price to pay for the end product, though. Here’s a summary of how I made said product:

(1) Gather walnuts—10 husks can produce a cup of ink. Juglans californica is listed as “uncommon” in the Jepson Manual (the California plant bible). The best place to find one is along the Santa Clara River or in canyons, anyplace the roots can tap groundwater. Once you’ve found the tree, expect walnut fruits in late summer. They’re peaking right about now. I usually gather the husks left on the ground after ravens and squirrels pillage the nuts inside.

These are ripe walnut fruits. The nut that lies within is small but edible.

(2) Find a metal pot to which you are thoroughly unattached, as you are about to ruin it. Juglone stains metal.

(3) Add the husks and a few rusty nails. The nails are really optional, but the iron they release will bind with tannins in the walnut husks to produce another, blacker compound that will darken the final product.[4]

(4) Barely cover with water. Bring to a boil, then simmer the walnut husk/rusty nail soup for about three to four hours. During this time, add additional water if necessary to keep contents from burning. The liquid will darken rapidly, but you need to boil it for a long time to get out plenty of color.

Hungry?

(5) Let cool. Boiling ink isn’t much fun to play with.

(6) Strain contents through a nylon stocking into a glass jar. You may want to reserve the boiled husks as they help future batches of ink get off to a good start.

(7) Feel slightly ashamed that you spent several hours making walnut ink, not widely regarded as a necessity to modern life.

(8) Use the ink to write, paint, stain wood, or dye textiles.

The pitchy brew shows as a nice sepia tone on paper. Since it was derived from a tree growing right here in SCV, you shouldn’t be surprised that the ink looks pretty but lacks depth.

WANTED: Walnuts

There’s an Indian riddle that asks: If acorns roll downhill, how can there be oaks growing on hilltops? The answer, of course, is squirrels, which are more than happy to run uphill to bury their acorns. They forget about a few of these cached treats and, voila, oak trees sprout on hilltops.

It’s a charming reminder that plants and animals have been helping each other out for a very long time. Plants help animals get food, animals help plants move around. People tend to exclude themselves from these relationships. Troublingly, this most natural of acts—give and take with a plant--feels distinctly unnatural to most with suburban sensibilities.

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As I mentioned before, walnuts are somewhat rare in California. Development has reduced their numbers so that the Southern California Black Walnut is listed as a "4" by the California Native Plant Society: "Plants of Limited Distribution--A Watchlist"[5]. My favorite tree in Santa Clarita happens to be a lonely walnut growing in the field near Old Orchard Road and Hart High School. It’s in the uplands next to the Santa Clara river, a big stately tree that likely outdates the powerlines that run overhead. Birds and rodents eat most of the walnuts, and those that survive and sprout will be mowed down to reduce the risk of fire in the field where the parent tree stands. This is precisely the sort of situation where people can help a plant out and probably ought to help a plant out since we contributed to its predicament.

After gathering husks, I’ll take a few good walnut fruits too, ones still on the tree but with brown mottling on the green flesh. I soak them a few hours at room temperature, peel off the husks and add them to the ink pot (payment from the tree!). Then, I toss the walnuts in the fridge until February to simulate winter. I remove them, and the warmth triggers germination. The resultant seedlings can be given to friends with room for such a tree, and walnuts can spread again through our valley[6].

Maybe one day Santa Clarita will have a new riddle: If walnuts roll downhill, how can there be walnut trees on hilltops? And the answer, of course, will be Santa Claritans.

[1]Sometimes Julgans californica ssp. californica.
[2]Do you miss O-chem too? Draw some organic molecules yourself by clicking here!
[3]Here's the juglone Wikipedia entry
[4]This website gave me the rusty nail tip and a general sense of how to proceed; it also contains some goo d links if you are overcome with the urge to make ink
[5]CNPS
[6] If you know of any walnut trees, please alert me as I’d like to preserve a little more genetic diversity than that inherent in the handful of tress I know of. And if you’d like to grow a walnut tree, email me and I’ll be happy to refer you to a seed source. They'll hurt or kill certain plants growing beneath them, but there are many juglone-resistant species as well.