This fall I treated myself to a class involving the use of natural dye extracts (made by the Earthues company) with cotton fabrics. As it is difficult to find information on the topic I thought to share some of my notes and general observations here for the benefit of others. The instructions will also work for dyeing cotton yarn, just be careful to skein it in such a way that it doesn't tangle.
The first step in dyeing cotton fabric using natural dye is to ensure that it is scoured of all natural waxes as well as added finishes that might interfere with the fixation of the dye. Of course this is also important when using fiber reactive dyes, but it is more so when using natural dye extracts. Starting with "PFD" ("prepared for dyeing") fabrics will help, but scouring even those would be wise.
The traditional method of scouring cotton and other cellulose fibers is to boil it well for several hours with a mixture of soda ash and detergent or some other wetting agent. The Earthues people sell a proprietary "scour" that we used in class but I don't like it-- the company is not forthcoming with information on what it is and it doesn't work well with fabrics you later intend to dye with madder. Instead, I would suggest using the wetting agent/detergent Synthrapol. It also is proprietary, but at least the manufacturer, ICI, will give you a MSDS for it, it is widely used, and is known to be effective in stripping unwanted substances from cotton fabric. Do not use standard laundry detergent because they contain "optical brighteners" which are actually dye. The brighteners will compete for the dye attachment sites on the fabric and affect the depth of shade you are going to get. Instead use some brand of detergent that doesn't have brighteners such as Seventh Generation, or us e plain hand dishwashing soap (but be warned that the latter two may foam up a lot). Needless to say, do not use fabric softener or any detergent that has fabric softener in it!
Step one: Weigh the fabric, ideally using a scale accurate to a tenth of a gram or better if you hope to have repeatable colors, and write it down in a place where you will be able to find it when you get ready to dye. If you are going to be dyeing many pieces of fabric it would be wise to mark the weight of the fabric on the edge using a laundry marker.
Step two: Weigh out an amount of soda ash equal to 2% of the weight of the fabric to be scoured, and "liquid scour" (or "Synthrapol" or other detergent/wetting agent, but you may have to adjust the amount) at 5.5% of the weight of the fabric. I like to use cheap plastic disposable drinking cups as weigh boats.
Step three: Starting with cold water, begin heating it in your dedicated dye pot. Always start with cold water because there are often metal salts and other things that will interfere with your dye that come from the hot water heater & pipes. The dye pot ideally should be non-reactive: stainless steel or enameled steel. But many report getting good, if different, results with aluminum pots. Whatever you are using, don't ever use the pot you use to dye in for food.
Step four: Once the water starts to get warm, add the soda ash and detergent and stir well. I find the best method is to fill the cups holding the soda ash and detergent with warm water from the pot, stir well to dissolve, and then add back into the pot, again stirring well.
Step five: Add the pre-weighed fabric and stir well. Stir frequently throughout the whole process.
Step six: Bring the temperature up to 180 degrees Fahrenheit over the course of 20 to 30 minutes or so. Hold at 180 degrees for another 30 minutes. Remember to stir the fabric frequently. If you are using fabric that is likely to need a lot of scouring, such as unbleached muslin, it won't hurt to keep this going a lot longer.
Step seven: Scouring is complete. Remove fabric from the pot and rinse in warm water.
Alum acetate is the preferred mordant for cellulose fabric. (Use good old "alum," potassium alum sulfate, for protein fabrics.) Be sure to use a dust mask when working with alum acetate in powder form, as the powder is typically super-fine and will do your lungs no good if inhaled.
Step one: Weigh out an amount of alum acetate equal to 5% of the weight of the fabric to be mordanted. I find that adding hot water to the weighing container immediately after measuring out the alum acetate is helpful in keeping the dust from flying around.
Step two: Starting with cold water, begin heating it in your dedicated dye pot. Once it is fairly warm, dissolve the alum acetate in the water, again using the method of first filling the weighing cup with hot water and dissolving the powder, and then stirring the whole into the pot.
Step three: Add the fabric to the pot, stirring well all the while.
Step four: Bring the temperature up to 100 degrees Fahrenheit over the course of about half an hour. Hold the mordant bath at 100 degrees for about one hour. Remember to stir the fabric frequently.
Step five: Mordanting is complete. Rinse the fabric gently and store for later use. The fabric is best stored in a bucket or Ziploc bag, covered with some of the mordant solution, until you are ready to dye it.
Step one: Measure out the desired amount of dye extract based on the weight of the fabric to be dyed and the depth of shade desired. (You remembered to write down what the fabric weighs earlier, right?) Medium colors will probably be in the range of 5% to 10% the weight of the fabric. If you are using plant materials instead of dye extracts you will be using a good deal more.
Step two: Starting with cold water, begin heating the water in your dedicated dye pot. Dissolve the dye extract in the water and stir well. If you are using cochineal and live in a hard water area, use distilled water instead of tap water. If you have hard water, some dyes (but not madder) may benefit from the addition of a small amount of sodium hexametaphosphate (a.k.a. Calgon water softener) before adding the dye extract. If you have hard water, gloat about it when dyeing with madder because you will get better colors than the folks in the soft water areas.
Step three: Add the fabric and stir well. Have the bath at about 100 degrees Fahrenheit.
Step four: Slowly (over the course of at least 30 to 45 minutes) bring the temperature up to 180 degrees Fahrenheit (or 160 degrees is using madder) and hold it there, stirring all the while, for another 45 minutes. Depending on the dye, you may want to leave the fabric in the dye bath while the bath cools down. Again, stirring is a good idea.
Step five: Remove the fabric and wash gently in lukewarm water using Orvus (basically pure sodium lauryl sulphate), or some other pH neutral detergent or soap. DO NOT use Synthrapol. Dry flat if possible.
Copyright Katharine Whisler 2006. All rights reserved.
With thanks to Pamela Feldman for sharing her knowledge.