Colors from plants have been used throughout history to enhance people's lives -- for decorating animal skins, fabrics, crafts, hair and bodies. They've been used to distinguish serf from master and to serve as banners in war. Your classroom garden, vacant lot, school grounds, and local grocery store can provide fuel for investigating the ways in which plants have enriched and continue to color our world. In doing so, your students can explore plants up close, design inquiry investigations, explore chemistry concepts, and have an intriguing lens for learning about history and other cultures.
ABCs: About the Botany and Chemistry of Dyeing
Invite your students to muse about why plants have so many different colors. What purpose might they serve for the plant? Have students recall what they've observed and already know about plants to help them consider this question. The green in most leaves is surely the most ubiquitous plant color. The green pigment chlorophyll in the leaves helps capture the sun's energy and convert it to chemical energy, which is then stored and used as food for the plant. Colors in flowers are adaptations that attract insects and other animals who, in turn, pollinate and help plants reproduce. Some plants have colorful fruits that attract animals who eat them, inadvertently spreading the plant's seeds as they do so. Scientists believe that other plant pigments may help protect plants from disease. Despite what we know about the role of a few of the thousands of plant pigments, the role of most colors in plants remains a mystery to scientists!
Most plant parts have a mixture of pigments, which is why dyes made from plants tend to appear more subtle and muted -- less "pure" -- than synthetic dyes. These "earth tones" in plant dyes intrigue many hobby and craft dyers, since the rich hues of mother nature, composed of many colors, all seem to "go together."
Although plants exhibit a wide range of colors, not all of these pigments can be used as dyes. Some won't dissolve in water, some will not hang on to fibers, and others will fade when washed or exposed to air or sunlight. It's not obvious from looking at plant colors which will reward us with vibrant dyes -- a fact that can lend shades of mystery and excitement to your classroom dyeing explorations.
It's generally easier to dye animal fibers like wool and silk than plant-based fibers like cotton or linen. Consider inviting your students to observe and compare different types of fibers or fabrics under magnifiers. The scale-like protein molecules in wool fibers provide a lot of active "sites" to which pigment molecules can attach. Cotton, flax, and other plant fibers, on the other hand, are made mostly of smoother cellulose, which has few sites available to combine with color molecules.
To help dyes bind better to fibers, dyers typically use different mordants, most of which are salts of metals like aluminum, iron, tin, and chrome. The word mordant actually comes from the latin mordre meaning "to bite," since early dyers thought these substances enabled the dye to get a better bite on fibers. Some dyes will bind well without mordants. Most plants will produce different colors depending on the mordant used. Since some of the mordants used are toxic, we only recommend one -- alum -- for classroom use. Tannic acid, found in many trees, can also act as a mordant. This means you can dye wool with black walnut hulls, which are high in tannic acid without adding extra mordant. You can also often affect dye colors by changing the pH of the dye solution, making it more acidic, for example, with white vinegar.
Dyeing ... To Get Started
Inspired to explore plant dyes with students, but unsure of where to begin? Investigating plant dyes can be as simple a project as simmering some onion skins, dipping in yarn, and observing to see what colors are revealed. Or it can be a more complicated project involving researching, gathering, and experimenting with different types of plants, mordants, and dyeing techniques. It might tie into a study of different cultures (e.g., Navaho) or periods in history (e.g., Middle Ages). In any case, we hope it will provide a centerpiece for stimulating student curiosity and questions, and lead to fruitful inquiries and adventures.
Finding Plant Materials
Your students can locate plant materials for dyeing from several sources. They can collect them in the wild, grow them, or purchase dye plants from a grocery story or catalog specializing in natural dyes. You'll probably choose some combination of sources. If you have a classroom garden, you may unintentionally grow some dye plants, since you can extract interesting colors from a range of common garden and roadside weeds.
If you collect plants or plant parts for dyeing, be sure to use plants that grow in abundance, taking care not to collect any rare or protected species. You will need a lot of plant material. A four-to-one ratio of fresh plant material to wool (by weight) for dyeing is generally recommended, and plant fibers like cotton require even higher proportions. That is just a ballpark number, though. We hope you'll encourage your students to experiment with different proportions of plant materials.
The list below includes just a fraction of the plants others have used to produce dyes. Exactly what results you will get depends on a host of factors, including soil type, moisture content, mordant used (if any), fabric, ripeness or freshness of the material, how finely you shred it, and proportion of plant material to fabric. Therein lie the mysteries and opportunities for your students to question and experiment. Don't let your students be limited by this list. Encourage them to observe plants in the environment, make predictions about new plant dyes, and investigate their theories. Students might want first to observe and create a list of clothing colors, then brainstorm natural plant materials they think might produce each color. Keep this list available throughout your dye project for reference and to inspire investigations and reflections.
Some Plants to Grow and Collect for Dyeing
Trees, Vegetables, Herbs, and Fruits
Getting the Color Out
Once your students have harvested plant parts and predicted which colors might emerge from which plants, consider having them brainstorm how they think they could "extract" the colors from the plants. Record their thoughts so they can set up investigations to test some of their ideas. Here's one method: Shred plant materials to expose more surface area from which color can be extracted. Cover the plant materials with water in an enamel pot, simmer them for about an hour until the water is colored and the plant tissues look bleached, then strain the dye bath through cheesecloth or an old stocking to get rid of plant material. (Some dyers do simultaneous dyeing in which the plant materials are left in when the fabric is dyed. If you decide to do this, place the plants or the fabric in an old stocking or net bag to protect the material from direct contact.)
Treating the Material
First, wash your fabric or yarn with soap to remove dirt and oils that could interfere with the dye binding to the fabric. If you're using a skein of yarn, tie it loosely so the mordant and dye can penetrate well. If you're just getting started and want to do some simple dyeing explorations, you may choose not to use a mordant to "fix" the dye. Some plants will yield colorfast dyes without a mordant (e.g., tumeric and black walnut hulls), and others may yield color without a mordant, but it may wear out with washing and sunlight (e.g., purple cabbage).
If you're using the mordant alum to help the dye bind better to the fabric, you can either pretreat the yarn or fabric (as is typically done) or try adding the mordant directly to the dye bath. You can usually find alum (make sure to get aluminum potassium sulfate) at a pharmacy or craft supply store and cream of tartar from a grocery store. To pretreat the yarn or fabric, measure 3/4 tsp. alum plus 1/4 tsp. cream of tartar per each quart of water in your dye bath. Dissolve this in a cup of hot water, then add it to a pot of water (one quart of water per each ounce of fabric). Wet the fabric to ensure penetration, then add it to the mordant solution. Heat slowly at a simmer for one hour. (Wool, in particular, doesn't respond well to rapid temperature changes.) Remove the pot from the heat, then cool and rinse the fabric before adding it to the dye bath.
Once you add fabric or yarn to the dye bath, simmer it for 30 minutes to an hour, turning the material gently. Stir and check the color every 10 minutes or so. Students may want to experiment by leaving the fabric in for different amounts of time, even allowing it to cool and steep in the dye bath overnight. Or they might want to do some "tie dyeing" to see what patterns emerge when they tie knots, rubber bands, or otherwise prevent the dye from penetrating throughout the fabric. Rinse dyed materials with progressively cooler water and hang them to dry.
Plant Colors Throughout History
Since prehistoric times, humans from across the globe have used plant pigments to enrich their lives. Historians and scientists believe that prehistoric animal skins and cave paintings dating back to 15,000 B.C. were dyed with plant pigments. They've discovered examples of early dyed fibers in Egypt dating to around 2000 B.C., and Chinese records revealing even earlier use of plants as fabric dyes. Ancient Britons, called Picts, used woad, a plant, to dye their bodies blue and frighten enemies in battle, while the British marched against the Americans in their well-known red coats dyed with madder root. Ask your students to imagine and discuss how they think early humans might have discovered that they could use plant pigments to color their bodies, hair, crafts, animal skins, and fabrics.
Natural colors have also played important roles as cultural symbols, often being associated with status, class, and religion. The less common reds and purples, for instance, were at times reserved for royalty, while more common dye colors were relegated to the "common" folk.
By the Middle Ages, dyeing had become an important industry in Europe. Farmers specialized in growing specific dye plants, and well-organized dyers guilds carefully guarded their craft secrets. Meanwhile, throughout the world, indigenous people were using native plant dyes for clothing, cosmetics, and crafts.
In the 1800s a scientist named Sir Henry Perkin was trying to synthesize quinine to treat malaria but, as often happens in science, made an entirely different discovery. He inadvertently produced the first synthetic lavender dye, which he called mauve. Mauve soon became the popular fashion color of the era. This discovery spelled the beginning of the end of the natural dye industry, and by the mid- to late 1800s, less expensive, more predictable synthetic dyes had replaced natural dyes. In this country today, natural dyeing is done primarily as a craft, often by those who knit and weave. Increasingly, however, people concerned about the pollutants produced by the synthetic dyeing process used in the textile industry are promoting undyed or naturally dyed products.
Using plant dyes to decorate eggs requires minimal materials and can spark explorations of different dye plants, concentrations, and dyeing methods. A basic method for dyeing eggs is to bring two cups of water to a boil, add plant materials plus one tablespoon of vinegar and simmer for at least ten minutes. Strain out the plant materials, then dip in and simmer eggs for at least ten minutes. If students use wax to draw designs on the eggs, the wax will resist the dye, and patterns will emerge. Some teachers report students creating intriguing patterns by wrapping and securing plant materials (e.g., cabbage leaves) around eggs before simmering them.