I recently took on a small weaving commission that required the use of black wool yarn. For a brief moment I contemplated purchasing the wool in the required color and then decided that I could dye it. I was surprised at how easy it was to achieve a rich, deep black color on the wool using only indigo and madder.
It inspired me to continue my current series of color studies, woven in cotton and linen, with an in-depth exploration of black dyes.
Initially, I wanted to achieve all the black hues without the use of an iron mordant. My years of mixing hues with primary colors gave me the confidence to believe that I could mix a good black for cellulose using 3 primary colors: blue, red, and yellow. The key was going to be finding the correct proportions.
The first step was to build up a deep layer of indigo blue (usually 8-10 dips in the vat) followed by a mordant, and finally red and yellow dyes. That red could be madder or cochineal but I chose to use only madder, since that is what I am growing in the garden. My preferred yellow is weld. Each different combination results in a subtle variation. Some “blacks” are more purple, while others are a bit more green, or brown. I began using black walnut and cutch as a substitute for the madder and weld and sometimes added madder or weld to those. Each is a distinct hue, and definitely in the “black” family. I am confident of the lightfastness of these hues because of the primary dyes that have been used.
These multiple shades of black, put me in mind of the paintings in The Rothko Chapel in Houston, which is the site of a series of large large “black” canvases by the artist, Mark Rothko. These black canvases are painted with layers of crimson, alizarin, and black.
But no exploration of black would be complete without some experiments using tannin and iron. Instead of building up layers of primary colors, I soaked the textile in a gall nut tannin bath, followed by a short immersion in an iron bath. I wanted to use as little iron as possible, but still achieve a very dark shade. I decided that 3% weight of fiber would be the limit of the amount of iron I would use.
Most often, I use ferrous acetate instead of ferrous sulfate because it is less damaging to the fiber. Cellulose fibers are are somewhat tolerant of ferrous sulfate so I did experiments with both. That is where I was most surprised! Without exception, the ferrous acetate resulted in deeper colors than the same amount of ferrous sulfate.
Why? I wasn’t sure. So I consulted my colleague, Joy Boutrup, who always knows these things.
“I think the reason for the grey instead of black with iron sulfate is due to the higher acidity of the sulfate. The acetate is much less acidic. The tannin complex cannot form to the same degree as with acetate.”
The pH of my ferrous sulfate solution was 4. The ferrous acetate was pH 6. (My tap water is from a well and is a slightly acidic pH6.)
The grey and blacks achieved with the tannin and iron are quite one-dimensional compared with those that result from a mix of colors and not nearly as interesting, Yet they are likely a more economical approach to achieving black; the multiple indigo dips, mordanting, and over-dyeing takes considerably more time and materials than an immersion in a tannin and an iron bath.
Always observing always learning, here in the mountains of North Carolina…
Natural Dye: Experiments and Results 
This is fascinating! I love the variation in the black panels.
Thank you for this clear analysis. And makes me aware how influencial the water pH can be
Good research. I will be trying an indigo vat soon. Have you tried goldenrod for yellow? Thank you.
I do occasionally use goldenrod when it’s in season but my go-to yellow is always weld. I harvested another good crop a couple weeks ago and it’s all hanging to dry.
I need to try Weld one day…
Thank you so much for sharing your experiments with us, very useful! I would like to know where I can get ferrous acetate. Could you share this with us?
You cannot purchase ferrous acetate. It would be too unstable. But you can easily make it using equal amounts of ferrous sulfate and sodium acetate. Joy and I have included this in our book, THE ART AND SCIENCE OF NATURAL DYES.
Very interesting research and results. I never thought of black with so many different possibilities of hues. Thank you once more for sharing your process and results.
This is absolutely totally fascinating and inspiring. I love what you are doing. Thank you for such indepth, as always, sharing. This will get me back to dyeing.
Thanks, Bhakti – always nice to have you on the other end of any communication!
very excellent work !
Fascinating and informative. Thanks!
Very intriguing experiments and process! You’re so generous to share your detailed information. Different hues of the black are beautiful. Thank you very much!
I have been able to get great blacks on silk by dyeing first with walnut, and then indigo.
Yes, it’s so interesting to change up the sequence of walnut and indigo – since neither dye require a mordant on protein, either sequence can be done.
Thank you for doing the research and sharing your results. So many possiblilities. The black shades on cotton are beautiful, as is the wool.
Tthanks!
Thank you Catharine. Have you experimented with Gypsywort?
No, I am not familiar with it. Does it make a good dye?
I’ve seen it written about in numerous places but no one explains how the dye was obtained. Some say the “fresh juice of the plant yields the dye, but the plants I’ve grown don’t seem particularly juicy, although it is August and perhaps I needed to extract it earlier in the season. No matter – I’m experimenting today; I separated the roots from the leaves/stalks, and will process them like most other plants (soaking, low heat). Will check back in if I get anything! – KC
As always, thank you so much for sharing your discoveries!
Tanks for Scharping your experience and Results.
Thank you for your blog posts. I’ve learned so much from them. In this post, I’m curious why you figure the strength of the iron after bath as a percent based on WOG. I have always made the iron solution for an after bath based on the strength of the solution, i.e. a .2% ferrous sulfate solution, and I use it multiple times without any apparent change in the effect. The process is similar to mixing a chalk bath for fixing a mordant, though the purpose is different. What is the reason to use WOG, or does it matter?
I think you can do either. I usually feel that I can control the amount of iron used for the given best when I use w.o.g. Then I don’t have to worry about the amount of liquid but just use whatever the textile requires for a full immersion.
Thank you for your blog and this post. It also shows clearly how colour is relative. We can influence the perception of colour by combining it with another one that enhances the effect we wish to achieve. Combining this black with its origins madder and indigo, as well as white, makes it look very black :). Lovely shades on cotton, too.
I love your very precise notes on your dyeing process. They are always so informative! I have dyed cottons with homemade iron solution and red maple barks. I happened to be house sitting where an old red maple tree was cut down! I harvested lots of bark and did some experiments! I’m not good at recording or note taking but I was pleased with the results. Oh and I was only interested in mark making not uniform overall dyeing. I’m thinking I will need to purchase your fabulous book!
Informed experimentation can be so rewarding! Thanks for your comment.
Thank you so much for all of the amazing research your share over your blog. This is a fascinating study of black dyeing! When using ferrous sulphate or acetate as a pre-mordant for wool, do you first heat with a tannin and then just dip in the iron bath after? Do you ever heat the fiber with the iron? And when you note that you decided to do 3% max iron for your study, does that equate to 1.5% ferrous sulfate and 1.5% sodium acetate? or does it mean 3% of each?
Hi Christine, I don’t use any form of iron as a pre-mordant for wool. It’s just not the way I work and most of my own textiles are done with cellulose fibers. 3% iron means 3% iron + an equal amount of sodium acetate.
Thank you so much for this post as I am in search of the perfect black for a project right now. I am wondering if there is any specific finishing that needs to happen after the ferrrous acetate when my linen cloth goes from indigo to tannin bath to ferrous acetate. Thanks again!
Any time that you use a form of iron, the textile should be washed very thoroughly with a neutral detergent.