More Notes on The Life of a Fermented Indigo Vat

Vat name: WEF (WEak Ferment)

Dates: June 2020-December 2022

The early months of the Covid pandemic proved to be the perfect time to delve deeper into fermented indigo vats. As I have discussed in earlier posts, I began making small (1 liter) sample vats and learning from them. Ultimately though, in order to really understand how the vats worked and dyed, I needed to commit to something larger. 

I built my first large (50-liter) fermented indigo vats in early 2019.

All the fermented vats were made using indigo pigment.   Wood ash lye or soda ash was added to provide the alkalinity.  They all  included combinations of spent madder root, dried Indigofera tinctoria leaves, and wheat bran to produce the fermentation which, in turn, produces the reduction.  

I frequently add small test vats to  larger ones as I build them. This “seeding” speeds up the reduction quite a lot, resulting in vats that are sometimes ready for dyeing after only 2-3 days, rather than the 10-12 days that would normally be required. 

These fermented vats were giving me good strong blue colors. Yet, I was also trying to understand and control a full range of light to dark shades of blue. I needed a weaker vat. Based on my experience with quick reduction vats, I decided to make an additional “weak” vat, by using only 2 grams of indigo per liter.

Note: when working with quick reduction vats, such as a fructose vat,  I can easily control the depth of color by making weak vats (1-2 grams/liter) vs. strong vats (5-8 grams per liter). This combination of both weak and strong vats is very helpful in creating shades from light to dark, and  when combing indigo with other dyes for greens, violets, etc. 

In addition to “numbering” my vats I also “name” them, using a title that is descriptive of the vat itself. This one was name WEF (Weak Ferment). Initially, it did NOT produce the anticipated pale color that I had hoped for. The color was actually quite strong, even though it contained what I considered only a small amount of indigo, compared to the other vats. From this, I concluded  that the reduction of the indigo in the fermented vat was much more efficient than in the quick reduction vats. 

In order to achieve the desired pale color from the vat I needed to deplete the indigo present.  Traditional vats typically give the palest of colors at the end of their life and this was very much in keeping with that strategy.

I began dyeing a LOT: large woven panels, cotton and linen clothing, etc. Because this vat was large (50 liters) it was easy to dye bigger pieces in this vat. I continued dyeing for a number of weeks, which turned into months. Still, the color remained deeper than I had hoped for. This was a lesson in patience.

Early in 2022, while working on The Studio Formulas Set for the Art and Science of Natural Dyes, a new recipe and color match project with Schiffer Publishing (more to follow about that later). The color samples in this project required careful control of my indigo blues (as well as all the other dyes). I was happy to find that my original “weak” fermented indigo vat (WEF) was finally dyeing beautiful pale blues, while my two other vats were still producing deeper blues. Access to both weak and strong vats was key to controlling the shades of blue.  

Six values of indigo produced for The Studio Formulas Set

Dyeing continued in the “WEF” vat on a regular basis for several more months whenever pale blue colors were required.

Each vat that I make is accompanied by its own small diary/notebook. In that book, I include all pertinent information, such as the original ingredients, dates, ph records, test samples, additions etc.  It is “the history” of that vat and an invaluable part of its life and maintenance. Regular maintenance always includes test sample dyeing, which is an excellent indicator of the health of the vat, as well as providing a record of the color that the vat is currently producing. 

In December, 2022 the WEF vat was finally depleted. It was producing no more blue color and resisted all attempts to revive it. After 30 months of use, the vat was consigned to the compost pile. 

The other two vats are still going strong today. One of them seems to be on its way to producing paler colors. 

14 thoughts on “More Notes on The Life of a Fermented Indigo Vat

  1. Thank you for your (always) detailed notes on indigo! A question-the large Weak fermented vat was maintained with the original amount of indigo and no more was added?
    Look forward to your new work (Studio Formulas).

  2. Catherine, What did you add for fermentation vat reduction over the life of the vat or did it just need stirring? I have had mine going for almost 3 years. It does get a bit unhappy if I neglect it. Judy

  3. I would like to know how large your vats are, what they are made of, and where to get them. My dyepots are a bit of a motley crew, two stainless steel soup pots, a crock pot, a single hot plate etc. Maybe you could do a blog on your set up. Looking forward to Fiber Forum class with you. Michaela McIntosh


  4. Thank you so much Catharine for a brilliant post. It is so fascinating to read about your experiments. Would you mind if I ask where you store your vats to maintain a certain temperature? Thanks in advance.

    1. My vats are in my unheated garage dye studio. Temps can get as low at 40 degrees F. Last winter I kept a bucket heater (with a thermostat) on one vat, while the others had no heat. All vats did just fine. Heat is important at the beginning of the vat when fermentation if developing but, based on my experience, I don’t thing it is necessary to maintain that heat at all times.

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