Chroma Sonorensis: Making ink from mesquite tree sap

Huge old mesquite tree on the Verde River in Arizona; from the US Forest Service publication Riparian Research and Management - Past present and future Volume 2

Drawing and painting in your journal with locally foraged wild pigments is deeply satisfying—true place-based art.

As part of my Chroma Sonorensis project, I began experimenting with making ink from mesquite tree sap—and I’m really pleased with the results. The mesquite (Prosopis velutina) is endemic to North America and an iconic tree in the Southwestern United States (though it’s now an invasive species plaguing nearly every continent). I grew up with mesquites, and especially love the huge old trees that are the remnants of the once-great bosques (Spanish for forest) that lined our now-dry rivers a hundred-plus years ago.

I gathered strips of bark from a tree in my back yard, where a lot of dark brown sap had leaked after a pruning cut last year. I soaked the bark in distilled water in a glass bowl, and then simmered it over a pan of barely boiling water for about four hours, until the liquid was very, very dark. I filtered the pigment solution through a paper coffee filter (several times, using clean filters each time). I then put the solution into the stainless steel pot and reduced it by at least four times by slow simmering, until only about half a cup of liquid was left—being very careful not to let it get to a rolling boil or burn. Finally, I cooled the liquid and added a very few drops of vinegar, and then decanted into small vials and a glass jar, adding a clove to each container (to help prevent mold).

The ink is a beautiful, rich brown that flows perfectly and adheres easily to the paper. Normally when making plant-based inks you must add a “binder” such as gum arabic (just a little) so the color adheres to the paper. But because this ink is made from sap it has a “built in” binder in the form of the slightly sticky sugars that occur in phloem (one of the heartwood tissue components in trees).

You can try making your own ink from lots of different sources. Berries can produce lovely inks though their color may fade or change color entirely over time. Dark-brown and black inks were historically made from plant-based sources of tannin, or tannic acid. Experiment! Try any tree sap that shows color, walnut hulls (not the nuts but the green fuzzy outer covering of the hard nut), and oak galls, which are not tree fruit but a nodule created by the tree in response to a little wasp (there are many species that do this) that lays its eggs in the oak leaf tissue and the tree actually forms the hard shell in response to the invasion. The baby wasps actually develop inside the round gall. You can read more about iron gall ink here, along with a good description of the ancient recipes for ink, including why vinegar is used.

Tips on using a Mini Plant Press

I’ve used my Mini Plant Press for decades to press flowers and leaves and small clippings of stems and even berries.

The Mini Plant Press comes with white cardstock paper, which will work fine for pressing most leaves.

Depending on the moistness of the plant parts, you may want to cut some newspaper or watercolor paper to absorb moisture if the plant parts are more succulent or you want to press berries or flowers that have a lot of flesh.

Tip: in erasable pencil, write on the white cards all the location metadata for your specimen: latitude / longitude, elevation, name of location and page number in your field journal where you will write up details of the collection: any other information about the habitat, nearby plants, anything you think is relevant to your specimen. Even include weather for the day if it’s relevant to, say, whether the flower is open or the leaves are closed up like in the photo above, showing classic nyctinastic leaf “behavior”—the Texas ebony’s leaves change orientation depending on light intensity and temperature. So I would add in my notes that the location was my backyard, and the weather is cold and cloudy.

After you load your cuttings and label them, reassemble your Mini Plant Press as shown, with the rubber bands evenly spaced to ensure compression. Times will vary widely as to when your specimens are dry, depending on relative humidity and the water content of the specimens.

I add my pressed specimens back into my journal (often leaving space for them) either by gluing in with archival-quality PVA glue such as Gamblin’s from an art supply store (works well for small leaves; even put the clear-drying glue over the surface of the leaf to help preserve it). I also save small plastic sleeves and bags in which to slide my pressed items, then glue or tape them in with white gaffer’s (washi) tape. Above you can see a pressed Alaskan fireweed flower in a sealed bag (important! so you don’t accidentally disperse seeds in other environments, potentially spreading invasive species) next to my sketch of the whole plant and a description.

This post is from my Tutorial on the Mini Plant Press: https://www.exploringoverland.com/field-arts-tutorials-list/2021/12/21/mini-plant-press-tips-on-using