I have always used silk as it is the easiest to work with. While using a mordant is fun, and offers up a wider variety of colors and effects, it is not strictly necessary for color fastness in most cases. This for the most part is because in the world of natural dyes opposites attract. So plant dyes adhere better to protein fibers than to plant fibers. Some prep work is in order to get the plant color to bond and last on cellulose fabric (i.e. cotton, linen, ramie etc.). With eco printing you can get color out of a lot of things immediately, but without a certain amount of experimentation over time, you won't know if the color will last, even on protein fibers.
The reason this comes up is people do ask me over and over if I would ever do cottons for quilting. I have done some linen for decorator pillows and some up-cycled linen clothing that has seemed to pass the test of time and washing. I chose the Japanese method described in India Flint's book, Eco Colour. The fabric is mordanted multiple times, going back and forth between a protein (in my case whatever cheap soy milk I can find) and an alkaline such as soda ash, letting it dry between mordant baths. Then the fabric is supposed to set around for a period of time (according to India the Japanese let it set around for five years! This is slow dyeing, but who has that kind of time?), I let it set for up to six months, but now some of the pieces I have are years old, so I am sure the mordants have more than bonded. I also knew then that cellulose fibers are very often exposed to tannins in order to make the bond between color and fiber.
Which leads me to this post. My daughter in law asks me about this every time we see each other. I keep saying that I will get around to experimenting some day. The thing is, I would hate to sell somebody yardage or fat quarters, they go to all the trouble to put them in a quilt of some sort and in a few years the color either faded due to minimal sun exposure or simply being washed. All that being said, I do see quite a bit of cotton being done and little mention made if there was any mordant used.
Part of the issue is that I wasn't really aware of a local, ecological sustainable form of tannin. I started pouring over my dye books and it turns out, according to one, you can get tannin out of acorns (also oak leaves, galls and bark). Since the acorns are the most readily available, that is what I decided to go with. Much fun has been made of the collection of acorns sitting by the studio door. Foraging for winter? New diet? Along those lines.
Now, this is where it gets sort of complicated. In one book it has you mordant the cotton with alum first, then the tannin. And the other book-you guessed it-has you do it the other way round and it also says to use some soda ash with the alum, where as the first book says nothing about that. Great. So, time to just give it a go. I found some white T-shirts on a clearance rack recently ($3 each, woo-hoo!) and decided since there were three exactly alike it would be a good way to test out both theories. I thought it better for the experiment to start with brand new, thoroughly washed shirts rather than chancing what a used shirt might have been exposed to in the past. The third one I think I will do the protein/alkaline thing and see if it looks any different from the other two.
1. Step one is supposed to be peeling the acorns. That ain't gonna happen so a zippy bag and hammer seemed to be the best route-and yes I realize the shells will have an effect, but I rather like those sorts of things.
2. I put the mostly smashed acorns in a jar that holds about a gallon of water.
3. Although I am usually not much of a stickler for water "quality" (Ph test strips? We don't need no stinkin' strips!) in this case I happen to know that you can make a gray dye of acorns with iron as an adjunct and the water pipe out to my studio is in need of a replacement. Last year we discovered that during the winter the water is quite rusty when we are not running irrigation. So, since my rain barrels are not in use at this time of year, I ran into the house to get water from there. I filled the jar with water. The goal is to have as little color change to the fabric to begin with so whatever you do next shows up better. I have made acorn dye before and it can turn out almost black.
As you can see, after just a few minutes the water is cloudy. This is the tannin being released out of the acorns. I did let it go overnight and when I got out here this morning it had turned amber. I have no idea if this is good or bad, it is probably the shells leaching into the water, so I strained it off.
I have a meeting to go to today, so hopefully tomorrow I can work on the T-shirts. Check back in, we can all find out together how this goes during the next month.