Rabbitbrush blossoming in October in the southwest corner of Salt Lake Valley, Utah.
In my STEAM it Up class at American Academy of Innovation, my students have conducted an inquiry lab that combines chemistry and technology with history and an ancient art form: dyeing cloth. I reported on a similar lab two years ago, but we have taken it much further and created an investigation that would work well for all chemistry classes without requiring too much equipment or expense. This activity fits in well with the NGSS dimension of science and engineering practices, as it allows students to identify variables, create experimental procedures, collect data, and report results in a fun and engaging way that incorporates art and the history of chemistry. Since dyestuffs are found around the world, there is also a global education component.
My STEAM it Up students collecting rabbitbrush blossoms near American Academy of Innovation (the bright orange building in the background).
We live in Utah, and there are a number of dyestuffs available that were used by Native Americans. Some materials, such as cochineal, were imported and traded for from as far away as modern day Mexico. Others are native to Utah, such as rubber rabbitbrush or Ericameria nauseosa. Our new school was built in a grassland area in the west side of Salt Lake Valley that was formerly used by Kennicott Copper Corporation (now Rio Tinto) as a mine and waste dump. After millions of dollars in cleanups, the site is now the new planned community of Daybreak, and our school is on the west edge near the South Jordan Trax Station. Since it is a former prairie, rabbitbrush grows around us in the empty lots right next to our school.
Preparing rabbitbrush blossoms for dyeing.
I had read that marigold blossoms make a good dyestuff, so on the day of our first attempt, I snipped half the blossoms off my marigold flowerbed (which grew up from last year’s seeds). My students and I took a mini field trip about 50 yards from the school where rabbitbrush was growing. It was the end of September and the brush was just beginning to bloom with bright yellow flowers in clusters. We collected several buckets. The species name of nauseosa is well earned, as the smell is a bit nauseating (some students are more sensitive to it and can get itchy eyes, so be careful of this). We also had walnut shells, cochineal, and the marigold blossoms as our dyestuffs.
Rabbitbrush blossoms ready for boiling in the dye bath.
Students teams of two each decided on a variable to test, such as the type and concentration of dyestuff; the type and concentration of mordant (a mordant is a metal salt such as sodium carbonate [washing soda] or alum powder [hydrated potassium aluminum sulfate]) that helps the dye bind with the fabric threads); the temperature and duration of the dye bath; and colorfastness (if the dye holds its color upon washing). They determined a procedure for testing their one variable while holding the rest constant. We then dyed small swatches of white terrycloth washcloths. A further variable could be the type of fabric used, but I only had the terrycloth for now. I hope to order some untreated cotton and wool yarn and dye them as well.
Rabbitbrush and marigold blossoms ready for dyeing.
Our basic procedure was to boil two Pyrex dishes half full with water. To one the mordant was added, to the other the dyestuff. The cloth swatches were first boiled for 10 minutes or so (depending on the group’s procedure) in the mordant, then the swatch was added to the dye bath.
We soaked white terricloth pieces in a boiling alum solution (the mordant), then boiled them in the rabbitbrush dyebath.
The results were excellent, and we were careful to label all the swatches with Sharpie permanent markers so that we could make comparisons after. We cut the dyed swatches in half and I washed one half at home in my washing machine. Each swatch was scanned into my computer and the eyedropper tool in Adobe Photoshop (you could use the Gimp as well) was used to sample three places on each swatch and record the RGB values. We averaged the values, and compared them to see which combinations of variables gave the best results.
We also dyed terricloth swatches with cochineal and an alum mordant.
We also tried adding more than one dyestuff to the same bath (doesn’t work well) and overdyeing, that is, dye a swatch with one color, then put it in a different color. We also tried an ornamental plant that was growing around our school, which I call firebrush; it has green to pink-red leaves (older interior leaves are more green). The firebrush provided great pigment upon boiling, and turned the cloth a nice pink color, but when rinsed out, the color gradually changed to a medium green. I suspected it might be a pH indicator, so I dipped part of one green swatch in vinegar and found it turned bright pink again. Only those two colors – green when neutral, pink in an acid. But it is apparently a good indicator and a fairly colorfast dye.
Our first dyed swatches, labeled with permanent marker. The left swatch is rabbitbrush, the second is marigolds, the third is cochineal without any pH modification, the fourth from left is cochineal with Cream of Tartar added, the last (right) swatch is cochineal with vinegar added.
As a further experiment, we tried adding Cream of Tartar or vinegar to the cochineal to see if we could turn it from magenta-burgundy to more of a bright red color or even orange, with mixed success. We got a bit more reddish color with Cream of Tartar, but never got to orange. Reading websites and other sources, I found that we need a stronger organic acid that wouldn’t dilute the dyebath, such as citric acid. To turn the cochineal more purplish, ammonia can be used. We also tried cochineal with rabbitbrush but still did not get an acceptable orange – just a salmon pinkish color. We need orange because our school colors are Innovation Orange (you can see our building from miles away, as the photos show) and Titanium (we are the Titans). We could also some other dyestuff, such as madder root, sandalwood, or safflower.
Swatches from our dye experiments. The ones on the bottom are pieces that have been washed to test colorfastness. The brown swatches are from walnut shells and hulls soaked in water over several days. Other swatches test different types of mordants (alum versus soda ash versus Cream of Tartar) or different concentrations of dye.
We experimented for several weeks with different combinations and the students wrote up their final conclusions. Here is what we learned: The best mordant for rabbitbrush, marigolds, and cochineal is alum powder. Cream of Tartar tends to gladden (or lighten) the colors, whereas soda ash (sodium carbonate) tends to darken or sadden the colors. Cochineal was less colorfast than we expected based on previous experiments, and tended to bleed all over the other colors when washed. Walnut shells seemed to do best with soda ash as a mordant. Overdyeing was only partially successful; we were trying to get a good orange and never did. The marigolds didn’t make a good orange either – but did do a nice golden brown color. Walnut shells with rabbitbrush made a nice golden tan, but cochineal with rabbitbrush depended greatly on which was dyed first; the overdye tended to eliminate most of the first dye.
The results of our experiment with firebrush, an ornamental shrub with green inner leaves and scarlet outer leaves and wicked thorns. The dyebath was bright pink, as in the swatch second to left, but when rinsed out it turned green as in the swatch second from right. I took a rinsed green swatch and dipped it in vinegar and the bottom turned pink again. Firebrush is apparently a pH indicator.
A final variable is to test different fabrics. I ordered more dyes, including madder and indigo, from Dharma Trading Company in November as well as untreated merino wool yarn and cotton cloth, with more alum powder and citric acid. Adding the citric acid to the cochineal did indeed turn it red (and eventually orange). Adding ammonia turned it purple. It worked wonderfully on the untreated wool yarn; I dipped one end in the regular cochineal and the other end in the cochineal with citric acid and got a beautiful variegated red to burgundy-crimson skein that held its color well upon rinsing and washing. The cotton cloth didn’t hold as well; I make the cloth purple to orange and even let it set overnight in the dyebath, but upon rinsing all the cloth turned back to a light magenta. The rabbitbrush made a nice soft yellow for the merino wool yarn.
Merino wool yarn dyed with cochineal. I varied the pH by adding citric acid to get the brighter red colors, and dyed one end of the skein with regular cochineal and the other end with citric acid treated cochineal to produce variegated yarn. Now to crochet it into a sweater . . .
My wife is amazing at crocheting, and my ultimate STEAM art product will be for her to use our naturally dyed merino yarn to create a sweater and a beanie. I also want use the dyed pieces of cotton to make a quilt in the shape of our school logo. I know several professional quilters who can do this for us. If the cotton isn’t accepting the dyes, then I must experiment further. Perhaps I didn’t soak the cloth in the mordant bath long enough. I am still experimenting with getting blue colors from woad and indigo, but more on this in a later post.
The Elements Unearthed 