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Eco-Printing is a process of transformation, in which the natural colorants in plant material unite with the metal salts in a mordant and the tannins in a blanket to create pigments that normally look very little like the original colors of the plant. As such, it reminds me of the complex processes by which alchemists attempt to combine natural chemicals to create the Philosopher’s Stone. In both cases, simple natural materials are joined and transmuted into something beautiful and often unexpected. Each of the three components in eco-printing can be adapted and adjusted to create nearly infinite variety in a finished piece. In this and the following two posts, I’m going to take a look at each of these components and the ways in which they can be used to create unique works of art.
Terminology: Almost everything you do in natural dyeing of fabric is based on the “Weight-of-Fiber” or WOF. To determine that, simply weigh your dry fabric. I find it’s best to weigh it in grams since it makes the calculations easier; ounces are fine too as long as your scale is accurate to a tenth of an ounce.
Before a fabric can be mordanted, it must be clean. During the process of preparing a cellulose fiber and weaving it, the cloth may become contaminated with chemicals like bleaches or sizing. Animal fibers like wool have naturally occurring oils such as lanolin; that’s what makes them so good at keeping you warm even when they get wet. All of these contaminants must be removed in order to ensure an even uptake of the mordant. This process of deep cleaning the cloth is called “scouring”.
To scour an animal (protein) fiber, soak it for two hours in warm water to which you have added a little pH neutral detergent like Woolite. Wring it out, rinse it in warm water until the water runs clear and proceed to mordanting.
To scour a cellulose fiber, you use sodium carbonate, also known as Washing Soda. Simply add about a tablespoon of soda ash to a non-reactive (stainless steel or enamelware) pot full of water, add your fabric and simmer it at around 180F for 90 minutes, then rinse it and wring it out. Or, even easier, add 1 tablespoon of soda ash to your washing machine instead of detergent and wash it at in hot (160-180F) water on the regular cycle. Then proceed to mordanting. If you don’t mordant the fabric immediately after scouring, pre-wet the fabric in plain water before adding it to the mordant bath.
A mordant, from the French word “Mordre” meaning “to bite”, is a base layer that allows the organic substances in the plant material to be absorbed into the textile or paper and become visible. In a way, it’s similar to preparing the soil for planting. The mordant influences the way the prints appear and is vital to fix the image and attain colorfastness. Any new or previously undyed piece of material must be mordanted before using it in an eco-print or the resulting print will quickly fade away when it is washed or exposed to sunlight.
Mordants are metal salts of various kinds and the one you choose will have a strong influence on the final look of your print even though the mordant itself may be invisible, or nearly so, on the fabric. The most commonly used mordants in eco-printing and natural dyeing are potassium aluminum sulfate (alum), aluminum sulfate, aluminum acetate, iron sulfate and copper sulfate. Tin in the form of stannous chloride can also be used but because tin is both toxic and damaging to the textile fibers, it is usually used in tiny amounts as an additive or “side-mordant” to brighten colors, especially reds and oranges.
Caution: Although many mordants are frequently used as additives in prepared foods in small amounts, when working with the quantities required for mordanting fabric it is important to play it safe and take precautions. Always wear gloves and a face mask when preparing mordant solutions and avoid getting the powders on your skin or in your eyes. A leftover N95 “pandemic mask” and a pair of kitchen dishwashing gloves will work great. This becomes especially important when using either tin or copper as a mordant or side-mordant.
Let’s take a look at each of the common mordants:
The first three, and by far the most often used, mordants are aluminum salts. Aluminum is what brings out and brightens the color in your plant material. In fact, without it you will probably get no color at all in your eco-print.
Potassium Aluminum Sulfate: Also known as alum, this is probably the safest and easiest to use mordant. It’s definitely the most common mordant to use with protein (animal) fibers like wool and silk but it’s also often used with cellulose fibers as well. It’s been around for a very long time, having been used in fabric dyeing since at least 500 BCE! It’s almost always used in combination with cream of tartar, which can be found in the spice rack at your local supermarket or purchased online. To use it, add 20% WOF alum (Weight of Fiber, see above; to get 20% WOF, you would weigh the fabric and multiply the weight by .2) and 6% cream of tartar (WOF multiplied by .06) to hot water in your dye pot and stir it until it’s completely dissolved. Add your fabric and slowly heat the water to about 180F, then hold it at that temperature for about an hour. Don’t let the water boil or you might damage the fibers in your material. After about an hour, rinse the fabric in warm water until the water runs clear. (Note: If you’re mordanting wool, be careful not to use cold water for rinsing or you will felt your fabric!) Squeeze out the excess water and hang the fabric on a line to dry. Once it’s dried, it’s ready to be used in an eco-print!
Aluminum Sulfate: This mineral salt is considered to be a little more environmentally friendly than alum because you can use it at lower concentrations. After mordanting, it’s usually given a second rinse in either wheat bran or calcium carbonate (chalk) to fix the mordant. To use it, add 15% WOF alum (To get 15% WOF, you would weigh the fabric and multiply the weight by .15) to hot water in your dye pot and stir it until it’s completely dissolved. Add your fabric and slowly heat the water to about 180F, then hold it at that temperature for about an hour. Don’t let the water boil or you might damage the fibers in your material. After about an hour, rinse the fabric in warm water until the water runs clear. Now it’s time for the fixing bath: If you’re using wheat bran, either wrap it well in several layers of cheesecloth or,as I do, stuff several handfuls of wheat bran into a nylon stocking and tie it closed. Put your bundle of wheat bran into a pan of cool water and squish it with your hands until the water turns milky looking. If you’re using calcium carbonate (chalk) instead of wheat bran, prepare a bath with hot water and 5% WOF calcium carbonate. Once the fixing bath is prepared, add your fabric and swirl it around, making sure it’s completely wetted. Rinse it, wring it out and hang the fabric on a line to dry. Your fabric is now mordanted and can be used immediately or stored for later use.
Aluminum Acetate *: Probably the most popular of all the cellulose mordants, aluminum acetate gives vibrant, long-lasting colors on fabrics like cotton and linen. It can also be used to mordant animal fibers like silk and wool where it works a bit more gently than the traditional alum and leaves the fibers a bit softer. In order for it to bind successfully to the fibers in your fabric, it does require an additional fixing bath in wheat bran or calcium carbonate. The recommended amount of aluminum acetate for mordanting is 5-10% WOF (the weight of your dry fabric multiplied by .05 or .1). Because aluminum acetate does not require really hot water a heat source isn’t necessary; you can just use plain hot tap water! I find that it dissolves best in hot water though, so I usually heat a small cup or bowl of water in the microwave, dissolve the aluminum acetate in that, and then add the resulting slurry to a non-reactive pot of hot tap water. Add your fabric to the pot, swirl it around and then let it soak, stirring occasionally, for 45 minutes. Now it’s time for the fixing bath: If you’re using wheat bran, either wrap it well in several layers of cheesecloth or, as I do, stuff several handfuls of wheat bran into a nylon stocking and tie it closed. Put your bundle of wheat bran into a pan of cool water and squish it with your hands until the water turns milky looking. If you’re using calcium carbonate (chalk) instead of wheat bran, prepare a bath with hot water and 5% WOF calcium carbonate. Once the fixing bath is prepared, add your fabric and swirl it around, making sure it’s completely wetted. Rinse it, wring it out and hang the fabric on a line to dry. Your fabric is now mordanted and can be used immediately or stored for later use. (The wheat bran stuffed sock can be re-used several times; just hang it up and let it dry out between uses.)
Other mineral salts for mordanting:
Iron Sulfate (aka Ferrous Sulfate): An iron mordant has almost the opposite effect of aluminum on fabric. Iron darkens or “saddens” colors and an iron mordant without aluminum will react with the tannins in plants to give a brown, almost black, color to the print. Because of this, iron by itself is not nearly as common a mordant as aluminum. Nonetheless it can be used as a stand-alone mordant or it can be added to an aluminum sulfate or aluminum acetate mordant bath to add some additional depth to the colors obtained from the plant material. A little goes a long way with iron sulfate; when used as a mordant, you typically will use anywhere from .25% to 1% WOF, although you can go up as high as 3% WOF if you want a really dark background. To use it, just dissolve the amount of iron sulfate you need in some cold water and add that to enough warm water in your non-reactive dye pot to hold your fabric. Add the fabric to the pot, swirl it around and let it sit for about 30 minutes. Then slowly heat the water in the pot to around 130F (about the temperature of hot tap water) and hold it there for another 30 minutes. Let the water cool, wring out the fabric and hang it to dry. Once it’s dry, rinse it well and it’s ready to use. Note: When used as a mordant with protein/animal fibers, iron sulfate can leave the fabric feeling rough and scratchy so use the least amount possible.
Copper Sulfate: Copper sulfate pentahydrate improves colorfastness in fabrics and also acts to shift the colors from plant materials and natural dyes. Like iron, it saddens colors though not quite as dramatically as iron sulfate. It also brings out blues and greens, making them more intense, and shifts yellows toward green. To use it, dissolve 4-5% WOF copper sulfate in hot water in your non-reactive dye pot. Top that off with enough cold water to completely cover your fabric, add the fabric and swirl it all around well. You can either let the fabric sit in the cold dye pot overnight or you can slowly heat the water to about 180F and hold it at that temperature for 1-2 hours. Rinse the fabric well and hang it to dry before using. Caution: Although copper is a necessary mineral for human health, at higher doses it can be very toxic. Always wear gloves and a face mask when working with copper sulfate!
Stannous Chloride (Tin): Tin brightens colors and really makes them pop out. However, it is the most toxic of all the mordants and tends to make fibers stiff and brittle, so it isn’t a mordant I recommend; I’m including it only for the sake of completeness. To use it, weigh out .5-2% WOF stannous chloride and dissolve it in hot water. Add that to a non-reactive dye pot filled with enough water to hold the fabric, add the fabric and stir. Slowly heat the water to 180-200F and hold it at that temperature for 1 hour. Remove the fabric from the pot, rinse it well in warm water and then hang it to dry. Caution: Tin is toxic! Always wear a mask and gloves while working with stannous chloride. Wear gloves while working with the fabric in the pot at least until it has been thoroughly rinsed.
To make enough aluminum acetate to mordant 1 kilo of fabric, combine in 3 liters of hot tap water: