Tannins or tannoids are a type of mordant that naturally occur in plants. If you are dyeing protein (e.g. wool) or cellulose (e.g. cotton) fibers with natural dyes, you need a mordant or fixative to help set the dye on the fiber. The mordant forms a coordination complex with the dye which attaches to the fiber. As a result, mordants enhance the wash- and lightfastness of the dyed yarn or fabric.
Some plants or dye materials contain tannins in high concentrations. In these cases, tannins can act as natural mordants which makes it possible to skip the mordanting part of the natural dyeing process.
I have written a post all about different kinds of mordant and how to use them. You can find it here:
What are Tannins?
Tannins or tannoids are a class of astringent, bitter compounds naturally occurring in plants. Those polyphenolic biomolecules are present in many different plants. They can occur in various parts of the plants, like the stems, buds, seeds or leaves. Tannins play an important role in the process of tanning leather. They also have antibacterial properties . And of course, in addition they are valuable for their use as natural mordants.
Tannins as Natural Mordants
Using tannin-rich dyes and omitting the mordanting step simplifies the dyeing process. Especially if you are a beginner in natural dyeing or just want to experiment with natural dyes for your personal use, this might be an interesting option for you. If you are concerned about the fastness of the dye, ask yourself the following question:
In my opinion, experimenting with different natural dye materials and the surprise of the final color results is half the fun of natural dyeing. I like to try all kinds of dye stuff from my surrounding area and observe how well the colors hold up over time. Sometimes this works out and sometimes it doesn’t. Let me give you two examples:
The term fugitive dyes refers to dyes that are not colorfast and will fade quickly over time and in the sunlight.
In my first year of natural dyeing, I was curious to see what kind of color I would get from elderberries. At first, they yielded a beautiful soft pink color. I was delighted and used the yarn to knit a pair of mittens for my daughter. However, since elderberries and berries in general are fugitive dyes, the color didn’t last very long. It turned into a beige within just a couple of months.
On the plus side, colors can always be overdyed to create beautiful, new shades. I don’t recommend using fugitive dyes if you are planning on selling the dyed yarn or fabric. But for your personal use, I don’t think it is as critical to produce only long-lasting colors. And remember that in general, all colors will fade over time, whether they were dyed with natural or synthetic dyes.
Examples for Fugitive Dyes:
- Red Cabbage
- Black Beans
Dyeing Experiments & Colorfastness Surprises
An example of a successful natural dyeing experiment are these pairs of socks. When hiking through the woods last year, I found a branch that had fallen off a pine tree. I collected some of the fresh pine needles and took them home with me. However, I couldn’t find pine needles mentioned as a suitable dyestuff in any of my natural dyeing books. I decided to give it a try nonetheless.
Since I sell my naturally dyed yarns in my Etsy Shop, I always thrive for high colorfastness. Although pine needles do contain tannins, I mordanted the yarn with alum. To further increase the fastness of the color, the green yarn was additionally modified with iron. It has been around nine months since I dyed those yarns and the colors have held up beautifully so far.
Tannin-Rich Dye Materials
Now, back to the tannins. Interestingly, the word “tannin” comes from the old German word “tanna” which means oak . Several components of oak trees contain tannins in high concentrations and are suitable for natural dyeing: the bark, the leaves and the galls which are also called oak apples. Oak galls are not produced by the tree itself but by a gall wasp that lays their eggs in developing leaf buds.
If you are looking for dyestuff with high concentrations of tannins to omit the mordanting part of the natural dyeing process, have a look at:
- Tree barks in general (p. ex. willow, quebracho, sumac, maple, wattle, eucalyptus, red mangrove, aspen, witch hazel, chestnut)
- Oak (bark, leaves, galls)
- Avocado pits
- Coffee, black tee
You can find more suggestions for tannin-rich dyestuff in the References & Further Reading section down below.
What are your favorite tannin-rich dye materials? How important is the colorfastness of natural dyes to you? Come share in the comments!
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References & Further Reading:
 Prabhu, K. H.; Teli, M. D. (1 December 2014). “Eco-dyeing using Tamarindus indica L. seed coat tannin as a natural mordant for textiles with antibacterial activity”. Journal of Saudi Chemical Society. 18 (6): 864–872
 https://www.fs.fed.us/wildflowers/ethnobotany/tannins.shtml (US Forest Service)
http://www.naturalmedicinefacts.info/chemical/22939.html (Examples for Plants containing Tannins)
http://www.naturalmedicinefacts.info/chemical/22939.html (More Plants containing Tannins)
If you live in the US or Canada and would like to know if a certain tree grows in your area, you can search for it here: https://plants.sc.egov.usda.gov/checklist.html