The Surprise of Indirubin!

Why would a white plastic button turn purple from an indigo dyebath?

Indirubin is one the most curious components of indigo. It is sometimes referred to as the “red” of indigo. Indirubin only occurs in natural indigo and you will not find it in a synthetically produced pigment. Indirubin is valued for its medicinal applications.

Some dyers have been successful at manipulating the extraction and pH of indigo in order to reveal the mysterious purple/red color of indirubin on a textile. I have no real experience with this process.

At one point I did learn how to analyze an indigo pigment in order to determine the presence of indirubin. If indirubin is present, it is an indicator that the pigment is made from plants and not synthetically produced.  Natural indigo has varying amounts of indirubin. The process of analyzing uses solvents and chemicals so it is not something that I want to do on a regular basis. 

I purchase all of my indigo pigment from Stony Creek Colors, as I know that their indigo comes from plants (and, consequently, contains plenty of indirubin).

Now that I maintain several large “active” indigo vats, I will occasionally dye a ready made garment. A white linen blouse is not a good choice for wearing apparel in the dye studio, but one that has been dyed a rich indigo blue is perfect. 

After dyeing, just before the final rinse, I always boil an indigo dyed textile in order to remove any unattached dye. Cellulose is boiled vigorously with a small amount of neutral detergent for about 10 minutes. Wool and silk are brought to a near simmer and held at that temperature for the same amount of time. 

Once I started using indigo from Stony Creek I noticed that the water from the final boil was always tinted a purple hue. I assumed this was the indirubin that was being rinsed from the textile. Interestingly, I observed that the purple color in the boil water is temporary, and will disappear as the bath cools. 

Recently, I dyed some linen shirts that had plastic buttons. The buttons stayed white until the final boil. When the garment was removed from the boil bath, they had become purple. I have now learned that indirubin is less easily reduced and the undissolved indirubin will stain plastics and other petroleum derived materials. Some of the polyester threads used to sew the shirts are also tinted purple. 

Summer Arrowood, the chemist at Stony Creek Colors, tells me that all the plastic vessels in her lab are dyed purple from the indirubin!

Will these buttons remain purple after multiple washings? I don’t know. There is always more to observe and learn from the natural dye process.

Slow Process

Natural dye has never been a quick way to color my textiles. First there is the mordanting, then the extraction of plant/insect material – not to mention growing, gathering, or drying the plants. Did I mention collecting seed? And what about the weaving, where I actually make cloth from threads? 

These last 18 months at home have been a chance to dive in deeper (and slower) with some processes. Just before COVID came to our doors, a friend gave me a small jar of sourdough starter. So yes, I am one of those who has made sourdough bread every week for the last year and a half. What a gift – both sour dough starter and the time to use it!

It was my fermented indigo vats that gave me the courage to take on sourdough bread making. I thought that if I could keep indigo vats alive for a number of months, then I could certainly keep a sourdough starter going as well. That has proved to be true.

The first fermentation vat was started in July of 2019. It was a relatively small vat (20 liters) but I used it a great deal. A year later it was used it to “seed” a larger 50 liter vat. The success of this first experiment gave me the confidence to start two more 50 liter vats in 2020. All are still going strong. Over the last two years I have made many additional one-liter vats in order to test reduction material, alkalinity etc. That first large vat that I created in 2019, after being used heavily for over two years, is finally giving me lighter blues.

Now I am in the midst of another slow process – sukumo. Debbie Ketchum Jirik of Circle of Life Studios very generously took a group of zoom class participants through the entire process of small batch composting of indigo leaves based on the teaching and book of Awonoyoh. Every 3-4 days we logged in, watched the sukumo being lifted from its container and stirred by hand. Does it need water? Does it need heat? What does it smell like? Conversations were focused and interesting. Several class participants were also in the process of making their own sukumo along with Debbie. I am not so fortunate. I have to gather more seed, grow more plants, and dry more leaves before I will have enough plant material to do my own composting. 

This experience has given me a far greater appreciation of sukumo. I was recently gifted a significant amount of sukumo and had planned on making my own large sukumo vat. Now, understanding more of what sukumo is, I am experimenting with using smaller amounts of sukumo in combination with my fermented indigo pigment vats. When I told my Japanese colleague, Hisako Sumi, about this, she indicated that Japanese industrial production has used this approach since early in the early 20th century. There is even name for this hybrid: “warigate”. Yoshiko Wada translated this for me as  “WARI GATE” / “split vatting” and it was mostly done using synthetic indigo. 

I have made many small test vats, using varying amounts of sukumo, in addition to indigo pigment and other materials to boost fermentation. These test vats were ultimatley used to ‘seed” a larger vat. I now have my own 50 liter hybrid vat that combines sukumo with Stony Creek indigo pigment.

My latest “slow process” is vermiculture. I recently spent an afternoon with friends, sorting worms from castings and beginning my own worm “farm”. This is another of those long term, slow processes that bring me closer to the earth, and makes me appreciate the small miracles of watching things grow. And I know that this compost will feed my indigo plants.

But not everything must be slow….

Stony Creek Colors has just released information about their newest product: IndiGold. It is a pre-reduced liquid indigo, grown in Tennessee and designed to be used in combination with fructose and lime (calcium hydroxide). I have dyed with the earlier available pre-reduced indigo but I was never sure exactly what it was and didn’t want to use the reduction chemicals that were recommended. I stopped using that product a long time ago when Michel Garcia introduced us to the “quick reduction” vats made with sugar and lime. But there are some occasions, particularly when teaching a one-day workshop, that it is impossible to make a vat and dye with it on the same day. 

Stony Creek sent me a kit for test dyeing and I was amazed at how quickly the vat was reduced and dyeing to full strength. It took only minutes – not hours. Stony Creek Colors told me that they”skip the chemicals” and use an electric hydrogenation process plus an alkaline to reduce the indigo. There are no chemical reduction agents! I used the vat all day long and it was still in reduction the next day. 

This will not replace my slow, fermentation vats but it will make “quick” dyeing possible when needed. 

Once again, Stony Creek is changing how we think about indigo and its production. They are currently posting information through a Kickstarter Campaign to support this new venture.