A New Use for Walnuts – The Indigo Vat

It’s black walnut season again in eastern United States – and soon the trees will be releasing their nuts and husks from the tree.


This summer I had the pleasure of teaching, again, with Joy Boutrup at Penland School of Crafts. As always, when Joy and I spend time together, we begin investigating and learning more about the practice of natural dyeing. 

We were experimenting with “quick reduction” indigo vats and the used of lime (calcium hydroxide) vs. lye (sodium hydroxide) as the source of alkalinity in the vat. We made a vat that was reduced with henna (Lawsonia inermis). This is the vat that I commonly use in my studio. The sugars present in the henna reduces the indigo.  Joy was looking at the molecular formula of lawsone, (the active dye ingredient in henna) and noticed that it is very similar to juglone (the active dye ingredient in black walnut hulls) They are both oxidation dyes, which means that they will dye protein without the use of mordants. 



The question: Could black walnut hulls be used to reduce an indigo vat in the same way that henna does?

We tried a small test vat. When I test a new indigo vat I often make it in 1 quart mason jars. This allows me to test multiple ideas on a small scale, without risking large amounts of dye or other materials. These small vats give me enough information so that I can scale up to a larger volume at a later time. I used 4 grams of indigo, two walnut hulls, and about 10 grams of lime. 


In June I had only whole frozen walnuts. I thawed them a bit, and covered them with water (no more than a quart, as this becomes the liquid for the vat).  As the walnut hulls softened more, I broke them up with my fingers and cooked them for a short time. The liquid was yellow. Joy cautioned against heating too much, which would turn the liquid brown as a result of oxidation. We wanted the oxidation to occur in the indigo vat.  So we stopped heating while the liquid was still very yellow. Next we strained the solid pieces out, and poured the liquid into the mason jar. We added the hydrated indigo and the lime.


Within a few hours we had a nicely reduced vat! I continued to dye test strips in the vat for a number of weeks. After a few days the color became lighter, but after the addition of supplemental organic materials (sugar, more walnut juice, cooked fruit juice etc.) the reduction improved and the blue color deepened as the indigo reduction improved. 

I  observed that after about 10 days the indigo blue got dull and the samples showed a wicking of a brown matter into the white cloth. Then, after about 30 days the color reverted to a clear blue again.  I described this to Joy.  She was not surprised and indicated that the juglone was by then inactive, having polymerized into a pigment that does not dye. Yet the sugars in the plant material continued to reduce the vat. 


I also tried adding puréed pieces of walnut hull to a test vat, but there was so much plant matter it made dyeing difficult – very messy. Thus, I now use only the liquid extraction. I have made several small vats since and they have all behaved consistently. 

When I collect this season’s walnuts I plan to scale up to a larger vat. 

In the spirit of understanding the plants that I use, this year I have planted a single henna bush in my garden. It will not winter over. It is not a local plant for me. I am thrilled to have discovered that walnuts,  a tree that grows locally in abundance,  can be used to reduce an indigo vat. 

23 thoughts on “A New Use for Walnuts – The Indigo Vat

    1. This is all still quite new to me, Amy so please let me know how it goes. I’m sure there is more to learn and refine. It seemed important to share this now while the walnuts are falling.

  1. My yard is full of Shagbark Hickory nuts – also juglone – but I don’t find much information about people dyeing with them. I’m planning on trying with them but feel free to talk me out of it if it’s pointless. Thanks so much for sharing your intriguing results.

  2. This is amazing! We have so many black walnut trees around and I occasionally run out of fructose and/or fruit to make my indigo vat!

  3. Thank you for this! We have so many walnut trees, so I will have to try to use them soon!
    Do you think this could be done using lye rather than lime? I wondered if that would have less sediment.

    1. The walnuts could probably be done with lye (sodium hydroxide) instead of lime. Joy and I have been experimenting with that but I haven’t reached conclusions clear enough to share yet. The henna, and likely the walnuts, require quite a high pH in order to reduce. But you’re absolutely right about it having less sediment with the lye .

  4. Very interesting! Does this new information change the process for dyeing fibers brown? In other words, I usually simmer the walnuts for hours to extract the dye. Should I stop when the liquid is yellow?

    I have three black walnut trees in my yard, and the nuts are already dropping with a thud. It seems early to me, but then I noticed that almost of of the nuts have scrap marks that look like squirrel teeth. 🙂

    1. I don’t know how the walnuts would work for reduction after they had been cooked for dyeing. We cooked them for only a short time and used the liquid while it was still yellow. Another experiment to try…

  5. Thank you for sharing!
    I have access to walnuts (Juglans regia) and usually use them for deep browns. For dyeing indigo blues I use fresh Japanese indigo leaves from my garden, not the powdered indigo. I wonder if this method also works with fresh indigo leaves. I would have to try … but the leaves are scarce and I wouldn’t want to loose any dye material … just can’t decide whether to try or not …

      1. Thank you Catharine! I love the utilization of local plants for the dye pot!We just had a black walnut tree fall during Dorian;wandering if I can use the dried leaves,(dried & powdered as Henna) for reduction?

  6. Catharine, Wonderful! This speaks to me as I try to use abundant, and even invasive plant material for dyeing. So many folks think the walnuts are a nuisance, and we can help them understand there is a place/use for every plant!

  7. Was thinking the leaves might work, though dont smell as strong as the walnut husk, so need more (or similar weight?). Recall when breaking up english walnut husks, could watch them oxidize to yellow befor put them in dye pot.

  8. Hi Catharine, thanks for your excellent blog sharing your dyeing experience and experiments! Have you done more with walnuts for reducing an indigo vat since this post? I’m excited for the prospect of a local and abundant reducing agent (plus I struggle with henna – filtering the paste after boiling the powder to extract the juice!). I’m especially curious about storing the walnut husks – the green outer part, right? And sounds like just gentle heating until the liquid is yellow? Thanks for sharing any more walnut tips!

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