Indigo Dyeing During Covid-19 Isolation

These last months, a time when I would usually be traveling and teaching, I have found myself  immersed in studio and garden. We are healthy and thankful for that. 

I am also grateful for the extended time to spend learning more about indigo fermentation. Over these last months I have made dozens of small test vats in the quest to better understand how the vats work and how to maintain them. These small vats have given way to a three 50 liter vats that are healthy and dyeing beautifully.

All of my vats use indigo pigment from Stoney Creek Colors, plus organic material to produce fermentation and thus, reduction. 

As part of the experimentation and study, I have successfully made my own wood ash lye and worked with both soda ash and potash as alternatives. All of these sources of alkalinity work with these vats. I have almost eliminated the use of lime, except as an occasional addition to adjust the pH.

Samples from the 6 batches of lye made from wood ash, ranging from pH 11.5-13.2.
sample vats
Sample indigo vats. Some are wrapped in electric heating pads in order to stay warm.

Each of the small indigo test vats (mostly 1 liter) are designed and made to answer a single question such as:

  • How long does it take a vat to go into reduction?
  • Does fresh ground madder root behave the same as “spent” madder root?
  • What is the effect of applying heat? 
  • How much heat?
  • Can soda ash be substituted for wood ash lye?
  • Can potash be substituted for soda ash?
  • Will “seeding” a new vat with a small amount from an older, reduced vat speed up the reduction process?
  • What is the effect of additional indigo plant material when added to the vat?
    • ground woad balls
    • dried Persicaria tinctoria leaves
    • patties made from Indigofera suffruticosa leaves
  • Can I make a fermentation vat without adding indigo pigment? All the indigo would then come from the plant material that also causes the fermentation. 
  • Can I leave a vat unattended for a week? 2 weeks? 3 weeks? how long?
  • What is the best way to get the vat back into a healthy reduction after it has been ignored and the reduction is weak or non-existent?
  • What is the best way to make a weak vat for pale hues?
  • Can a fermentation vat be done successfully using synthetic pigment? – I was not successful at this!

Small samples are dyed daily in the sample vats and I monitor  both the pH and the temperature of the solution. I also take note of both the vat surface and its smell. Once I feel “confident” that I have learned the lessons that each experiment has to teach me, I add the small vat to one the large ones. This replenishes the volume and adds some organic material.

indigo vat comparsion (1)
alkali comparisons

Making the first “large” vat took courage and a leap of faith. I now feel ready to double the size.

Several years ago I began growing small amounts of indigo in my garden, simply to understand it. I knew it would never be practical to extract my own indigo pigment. Now I have found an important use for even the small amounts of those fresh indigo leaves as source material for indigo balls or dried leaves to be added to the fermentation vats. 

Earlier this month I “attended” a “Zoom” talk by Aboubakar Fofana in which he talked about his own indigo practice. It was hosted by Botanical Colors.  I think it is well worth you time and now available online.

The indigo research and opportunities to attend virtual lectures have become possible because of this focused time at home. Now, it’s time to go back to the loom and prepare some woven shibori textiles for dyeing!

indigo vat comparsion
Four different values of indigo dye from the fermentation vat.
woven shibori shawl, made and donated to Penland School of Crafts annual auction
Woven shibori shawl, made and donated to Penland School of Crafts annual auction

25 thoughts on “Indigo Dyeing During Covid-19 Isolation

  1. Thank you for this fascinating post about your current exploration of indigo and its response to such a wide range of alkalinity sources. Your samples are really enlightening.

    On Fri, Jun 19, 2020 at 4:09 PM Natural Dye: Experiments and Results wrote:

    > Catharine Ellis posted: “These last months, a time when I would usually be > traveling and teaching, I have found myself immersed in studio and garden. > We are healthy and thankful for that. I am also grateful for the extended > time to spend learning more about indigo fermentation” >

    1. I’m actively working out the answers to these questions and discussing with Joy. They are complex and not within the scope of a blog to explain thoroughly. Joy and I have talked with our publisher about the possibility of a 2nd edition of The Art and the Science of Natural Dyes, which would include the fermentation vat and a number of lessons that I have learned since we wrote the first edition.

      1. That sounds like a good idea.Would you consider, since it is a loose leaf publication, issuing an addendum for those that already have the first edition…?

  2. Pingback: oh so blue |
  3. This is sooooo awesome. Thanks!

    On Fri, Jun 19, 2020 at 4:09 PM Natural Dye: Experiments and Results wrote:

    > Catharine Ellis posted: “These last months, a time when I would usually be > traveling and teaching, I have found myself immersed in studio and garden. > We are healthy and thankful for that. I am also grateful for the extended > time to spend learning more about indigo fermentation” >

  4. Catharine you are so generous with your information and processes. Your questions should inspire others to investigate for themselves, not just wait for the answers! Thank you!

  5. Such a great job… According oneself the time for experiment is certainly the best opportunity to understand complex processes like fermentation vats. I as discouraged to test fermentation indigo vat because I thought what a minimum (50L at least) volume was required. But you work with as small as 1L ! Are there particular issues to work with such mini testing vats?

  6. Thanks for sharing everything you have learned from doing the experimentation! Such great information! Bravo!

  7. Your’e right, it would be pretty scary to start out with a 50 liter vat without the confidence that it would work. I was actually quite surprised (and pleased) that it translated so well to this small volume. Not all processes will work when they are cut down so much in size.

  8. Hi,

    I’m looking forward to purchasing the addition to your work, with all the indigo vat information!

    Thank you so much for sharing the knowledge, it’s been invaluable to me. I’m going to start a small indigo plot next year in my garden.


    Mary Marvelli

  9. I attended the same presentation and found it really inspiring.I love that he refers to himself as an indigo addict rather than a master!

  10. I will be interested in your thoughts on maintaining a vat for very pale shades. I have been tending 2 10 gal henna indigo vats ( that I thought were fermentation!). one being very weak to enable me to dye a range of pale blues that are relatively stable. From your recommendations, my minimum due time is 5 minutes, but more often 10-20 minutes. This pale vat goes out of balance very easily!
    I’m so looking forward to learning this true fermentation method, and have ordered some indigo seeds to plant in anticipation of starting one. I’m in the Deep South so I’m going to try growing Indigofera suffruticosa.
    I look forward to hearing more! And yes to the book addendum!

    1. I am still working on making successful weak fermentation vats for paler colors. In the past, when I wanted pale colors I would usually make a fructose vat with 1-2 grams of indigo per liter. I make it with the idea that I would only use it for a limited amount of time and then discard it. I use the henna vat for stronger colors when I plan to use the vat for a long period of time.

  11. I have started co-mingling the vats to keep the light one going. Giving it a jolt by adding a couple of cups from the dark vat if the pale vat can’t seem be revived. Since I’m always adding rinse water back to refill, I’ll also steal from whichever vat is not in use at the moment. Someday I hope to take an indigo class from you, I still have so many questions!!!

  12. Dear Catharine, thank you so much for sharing all this knowledge on indigo, definitely looking forward to a published version of results to complement your book. I will have to try more with woad, but somehow the days just seem to fly by. Carolyn

  13. Hi Catharine (and Joy!), Wonderful that you two are continuing to explore. The Maiwa course that you two taught reflected your deep commitment to science-based learning and generous sharing. Could you please comment on the difference between alkalinity and pH? You mention using different sources of alkalinity, reserving lime for adjusting pH. I’ve had several 15-20L indigo vats, and thought my pH meter was all I needed. Thanks for this blog and all you do for the dyeing community. I also hope for an addendum on indigo to your first book, as indigo is my main interest. Warmest regards, Cassandra

    1. pH refers to the measurement of acidity or alkalinity. pH 7 is neutral. Anything that measures above that is alkaline and anything below is acid. Lime (calcium hydroxide) is a strong alkaline substance. Other alkaline sources include wood ash lye, soda ash, or potash. I’ve been experimenting with all of these in the fermentation vats, though the quick reduction vats seems to do best with the lime.

  14. Catherine, this article ( says: “ The major components of wood ashes are potassium carbonate (potash) and sodium carbonate (soda ash). From a chemical standpoint these two compounds are very similar. So similar that while ashes have been used for millennia the difference between sodium and potassium carbonate was only recognized in the 19th century. The elements in the first column of the Peridic Table, containing sodium and potassium, are called the alkali metals.”

    From that, I gather it is possible to use both soda ash and potash in the same vat. I hope. I got red potash yesterday, for its residual iron, added 1 ounce to my 5 gallon vat and stirred. This morning, my fermentation vat had a 1” flower, some coppery sheen, and an ammonia-type smell.

      1. That’s a relief! 😇 before I out in the red potash, I wanted the iron in there, the vat had a musky smell. Now it stings my nose a bit. I don’t know if that is the norm, perhaps you can guide me on this? A bit of an ammonia odor? I was reading Asian Textiles about adding morinda to get a darker color, all about the tannin perhaps. Well, I’m using a raw teak rod to stir the vat and hoping that adds something. The alternative is to go down to the teak stand on the next street aand get a handful of old leaves

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