Small-scale Indigo Processing

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So you're growing Japanese indigo (or other indigo-producing plants) in your garden this year. You planted the seeds, cared for the plants... maybe you have even harvested some leaves and done a fresh indigo dye bath. But what do you do if you want to have homegrown botanic blue at your fingertips in the months of winter?

If you are familiar with traditional Japanese indigo processing, you may have heard that that the making of sukumo (composted indigo) generally requires 300 to 450lbs of dry indigo leaves, a composting floor, and three and a half months. This method (a variation of which is used in traditional European woad production), produces a precious, concentrated pigment in the form of compost, which can be stored indefinitely and added to fermentation vats throughout the year.

Making a hot compost pile in the traditional Japanese fashion reportedly requires growing, harvesting, and drying around 5,000 indigo plants... which is not really possible for those of us who grow indigo on a garden scale.

I grow Polygonum tinctorium in three places: my home garden, my parent's garden, and the garden where I work. Combined, this now amounts to between 200 and 500 plants, depending on the year. In order to gather enough leaves to make my own compost pile, I would need to harvest, dry, and store my indigo crop every year for the next several decades... that is, unless I move to somewhere where I can start the farm of my dreams! Anyway, you get the point...

While I would like to dispel the myth that this is the only way to make sukumo (it is actually possible to compost smaller quantities using a slightly different method), I prefer to use the process described below, which is straightforward and produces isolated indigo pigment instead of compost. Once dried, this pigment can be used in traditional indigo vats, or added to soaps, botanical inks, etc throughout the year.

Below I will show you how to isolate indigo pigment from your plants for storage and future use. The method I use is one adapted in various forms around the world--Southeast Asia, India, Central America, the Southern US... on a large scale, it is most appropriate for tropical climates (where hot weather aids in large vat fermentation), but on a small scale it can be used by anyone who has a sunny spot where summer temperatures rise above 70 degrees (F). Any species of indigo-producing plant can be used.

 

The following process is broken down into five basic steps:

1. Ferment

2. Alkalize

3. Aerate

4. Concentrate

5. Strain & Store

Tip: if you have only a few plants to work with, I would recommend using the Indigo Summer Dye Recipe I have put together, substituting hydrated lime for baking soda (see this post for more information on choosing alkaline agents). To save your pigment rather than do a dye bath, stop after aerating the bath and allow the pigment to settle... then you can follow steps 4 & 5 listed below.

 

What you will need:

-A large plastic bucket, storage tub, or livestock tank (preferably dark in color). For this demonstration I have used a 36-gallon, dark blue storage container.

-Freshly harvested indigo plants--enough to pack into your container with some space to spare at the top. Here my container is filled with the stems of seven healthy Polygonum plants, which were cut 4-6" from the base to allow for regrowth and a second harvest.

-Non-chlorinated water (this is a fermentation process, which can be negatively affected by chlorinated water!)

-Slaked lime (calcium hydroxide, also known as pickling lime)

-Weights and galvanized fencing, or some other way to hold the plants beneath the surface as they ferment.

-A tarp, lid, or clear plastic sheeting to cover

-A sunny spot (or greenhouse) and several warm, consecutive days.

-Citric acid (for neutralizing leftover lime water)

Recommended:

-Extra buckets for decanting and storing water

-A sturdy leaf rake that fits inside your container (if you are using a larger one)

 

Tip #1: if you want to keep track of pigment yield from year to year, consider weighing and recording the plants you harvest before starting.

Tip #2: if you live in a cooler climate, or are doing this process in the fall when temperatures are lower, consider using space in a greenhouse. Another trick is to lay out a long hose in the sun and pressurize it, then fill your fermentation container in the afternoon with the hot hose water to give fermentation a jump... then cover the container with a sheet of heavy-duty clear plastic to help it heat up during the day.

Tip # 3: while the first few days of this fermentation process produce a lovely, almost floral smell, things inevitably degenerate from there... as you may well know, there are a wide range of smells associated with the various stages of indigo processing and dyeing, and while us indigo lovers may come to adore them, our family members may not! Be forewarned that this process might need to be done entirely outside, away from the general public 🙂

Ferment

Pack the plants (stems and all) tightly down into your bucket or tub and fill the container with water to cover the plants. Cut a piece of galvanized fencing to fit in your container, and place weights (ie clean bricks or large rocks) on top to keep the plants below the surface of the water. Here my piece of fencing was just large enough that I had to bend the corners in slightly to fit it in the tub--and the tight squeeze provided enough pressure to hold the plants under water.

Cover the container with a lid or tarp, and let it sit in a warm, sunny spot for 3-5 days. After a few days, the liquid will  take on an almost neon cast. During this time, if any stems rise above the surface, tuck them back down beneath the fencing. When the water looks like antifreeze, it is ready for the next step (see photo).

Remove the plant matter, which can now be disposed of on the compost pile. The leaves should be mostly brown and a bit slimy by now--if a large portion of them are still bright green, you can move the plants to another container with fresh water and allow them to ferment a second time to extract additional pigment.*

*According to the research papers I have come across, indoxyl (indigo pigment's precursor)** is fairly unstable at this point, and it is better not to let it ferment too long or it will begin to break down... therefore, if the weather and water were not warm enough to fully break down the leaves within the initial 3-5 day period, I prefer to do a second ferment--this usually takes only a few days more, and insures I maximize pigment harvest).

**Fresh indigo leaves contain indican, which is broken down into indoxyl (indigo pigment's precursor) during the fermentation process. The bright-colored fermented liquid you have contains indoxyl... in order to turn it into indigo pigment (aka indigotin), you will first need to alkalize, then aerate the bath.

Alkalize

(See this post for more information on choosing alkaline agents)

After discarding the plant material, remove some of the liquid with a small bucket. Add approx 1Tbsp slaked lime per gallon of water to this bucket. My 36-gallon tub was about half-full after removing the plant material, so I added 1 cup + 2Tbs (18Tbs total) slaked lime powder. Stir vigorously to dissolve, then stir this liquid back into your large container.

The pH of the entire bath should now be between 9 and 11.

Use caution when adding slaked lime to water, as the solution will be highly alkaline. Avoid splashing the liquid, and if it gets on your hands or skin rinse immediately with fresh water.

Aerate

Depending on the size of your container and how full it is, you can approach oxidation in several ways:

-pour the liquid between two containers of the same size (great for gallon jar or bucket-scale experiments)

-use a broom or rake to vigorously swish the water around (my favorite for larger tubs and livestock tanks)

-use a smaller bucket to pick up buckets of water and pour them back into the bath (may work for you, but I do a lot of bending and lifting already at work, so I prefer the rake method to save my back!).

-get creative... The point here is to introduce as much air as possible into the liquid, as oxygen will turn the indoxyl chemical compound into indigo.


In India, where this method is employed in large-scale production, they use a series of giant cement pools in which groups of workers physically kick the water around to aerate it. For more on this, I would recommend taking a few minutes to watch this video...

...though I don't know that I would recommend doing it that way, given the high alkalinity of the water.

You will notice as you work that the foam you create will turn blue with exposure to the air, and gradually you may see blue (or teal-colored) pigment precipitating out of the solution-- Very exciting! Focused agitation for 20-30 minutes should be plenty, unless you are working at a larger scale (the large cement tanks used in India are reportedly agitated for around two hours). A large livestock tank can be worked by several people at once using rakes to make things go faster.

Stop once the liquid turns reddish brown... you will need to stop agitating and let the pigment settle for a moment or two to check this (see photo). At this point the foam may have stopped turning blue, or disappeared altogether.

Concentrate

Now it is time to wait... after a few hours, the indigo pigment will have settled to the bottom and you can carefully decant the clear brownish liquid.

Save this liquid so you can properly dispose of it! Remember that it is highly alkaline, and it is very important to neutralize it with citric acid before dumping it outside or in a septic system. If you live in an area where drought is an issue, neutralized water can be saved and reused to ferment another round of fresh indigo, or for making indigo dye vats (if you are going to make an indigo vat out of it, there is no need to neutralize the water--it is already the perfect pH!) .

Be careful not to disturb the sediment at the bottom as you work--as soon as you see the pigment stirring up, take a break and walk away for a bit to let it settle back down before continuing to decant. As most of the liquid is decanted off, the slurry can be transferred into smaller buckets or jars and allowed to settle (this makes it easier to continue decanting liquid). If you like, a simple siphon can be made to make this process go faster.

Let the pigment settle, decant, move to a smaller container. Continue this process until you have a concentrated slurry of pigment.

Strain and Store

Once you have removed most of the liquid, it is time to strain the indigo pigment to remove bits of leaf and debris. Using a fine mesh colander/strainer, carefully transfer the pigment slurry (which may be more of a sludge at this point, depending on how meticulous you were in decanting) through the strainer. Pour some clear water through the leaf bits in the strainer at the end to wash any remaining pigment from the strainer.

Once this is done, I like to take the strained pigment and add it to a 5-gallon bucket full of fresh, hot water, stirring vigorously and then letting it settle and decanting one last time to dissolve bits of lime that remain undissolved... if you skip this step, that's fine--your dried pigment may be lighter blue in color (due to the presence of residual lime, and perhaps some disintegrated plant matter, neither will have a negative impact on your future vats).

Once strained, the liquid pigment can be stored in glass jars for up to a year, or dried in the sun for indefinite storage. Your pigment can now be used in future dye baths, homemade soaps, etc... congratulations!

PS. For drying, I have made a square frame out of wood, and stapled hardware cloth to one side. Placing the frame mesh-side down over a basin, I lay 2 wet pieces of muslin inside the frame, large enough that the edges flow up and over the sides. On top of this I lay a piece of wet 8mm habotai silk of the same size. The muslin protects the silk from the hardware cloth, and the silk catches the indigo pigment while allowing any remaining water to filter through into the basin. The pigment can be left on the silk in the sun to dry. At this point it is still pretty stinky, so you may also want to place a window screen or something similar over the top of the frame to keep bugs from drowning as the water filters out! When it is all dry, it can be peeled away from the silk and stored in chunks or ground into powder.

Home grown indigo.

 


 

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17 Responses

  1. Trilby
    | Reply

    I just wanted to thank you for this clear and helpful post. This is my second year of growing indigo in my garden, and this year I had about 100 plants. I was really excited to find this post (through fibershed) recently, and learn I did have enough plants for a ferment after all.
    Do you have any recipes to recommend for using the indigo pigment? I have only dyed with the fresh leaf so far.
    Also your website is beautiful– very inspired by your work.
    Thanks!

    • ecotone.threads@gmail.com
      | Reply

      Hi Trilby,
      Thank you, I am glad to know that this information is useful to you! I will put “Homegrown Indigo Powder Vat Recipe” on my list of future blog posts, in the meantime, Aurora Silk’s website also has this recipe: http://www.aurorasilk.com/tutorials/how_to_natural_indigo_dye_vat.html, which explains how to make a fermentation vat.

      For some people, fermentation is difficult because it requires a high temperature (85 to 110 degrees F) maintained over many days to encourage the right microorganisms to grow and reduce the oxygen in the bath. In this case, it is also possible to do a chemically reduced vat with powdered indigo, in which case I would recommend this recipe: http://www.dharmatrading.com/information/how-to-dye.html (though if you have a septic system I would recommend substituting slaked lime for soda ash at a rate of 1Tbs/Gallon, as it is less dangerous to neutralize if you want to dispose of the vat water later).

      Best wishes!
      Kori

  2. Marnie Jackson
    | Reply

    Great blog site loved the video of India! Very informative. Thank you.

  3. Vitaly
    | Reply

    Hi! Once again, thank you for the great post! Very detailed, informative, and well organized!

    • ecotone.threads@gmail.com
      | Reply

      Thank you Vitaly! It is so good to hear from you!

  4. azure keahi
    | Reply

    i’ve been reading / watching every tutorial i can find about processing fresh plants and this has, by far, been the most useful. i have around 25 japanese indigo plants & want to attempt this process, but am wondering if that is practical. would you suggest a fresh indigo dye bath or fermented dye bath for 25 plants? thank you so so much for putting this article together.

    • ecotone.threads@gmail.com
      | Reply

      Hi Azure,
      Thank you for your comment! With 25 plants, you could really go either way. I prefer the fermentation method for medium sized batches because whole plants can be cut and fermented stems and all (rather than stripping the leaves to make them fit in a container on the stove top). It also saves having to have the stove on all afternoon, while carefully monitoring the temperature to make sure it doesn’t overheat and denature the pigment precursor. The flip side is that the process is extended over several days, and you need to be ready to alkalize and aerate the bath as soon as it is ready to go, as leaving it to ferment too long results in lower pigment potential.

      I hope this helps, Please feel free to let me know if you have any other questions!

      Warmly,
      Kori

  5. Lynn
    | Reply

    Hi Kori,
    Thank you for this information. Am bringing back my old natural indigo fermentation vat.
    It is small but seemed to work first time tried, though has been a puzzle.
    First yarn did a quick dip and pulled out dark teal blue, but later after dried tried to wash it off as heard
    it crock and not be washfast if not first yellow/green . Keep outside in heat of day.
    Found this on woad study published, interesting but they didnt get good results from the fermenting part.
    http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-89132015000100096
    Am wondering all the things that effect the colors from indigo and amount extracted being for immediate use or storing pigment.
    Noticed after extraction and when dying that on some YT Japanese dying they put right into water and swished. With the yarn, they slapped it against the floor. Is this oxidizing it more completely I wonder.

  6. Adrienne d'Evreus
    | Reply

    Am trying to make blue pigment to paint medieval style miniatures with from my Japanese Indigo this year and am going to use your post. Thanks so much for your effort and sharing this with us!! When I write up a blog post about my efforts how should I give you credit?

    • ecotone.threads@gmail.com
      | Reply

      Hi Adrienne,
      My sincere apologies for this late reply! Life has kept me away from the computer the past month. This sounds like an incredible project you are doing, I am looking forward to seeing your results. If you would like to credit my article, a link to the blog post would be perfect. Thank you for asking!

      Warmly,
      Kori

  7. Madhav
    | Reply

    Thank you very much, Kori.
    This was such a beautiful presentation. I’m growing some Indian Indigo (Indigofera Tinctoria). and considering doing some cotton dyeing for cushion covers.
    It was so helpful.

    • ecotone.threads@gmail.com
      | Reply

      Thank you Madhav! Wishing you the best in your indigo journey, I would love to see what you create with your homegrown indigo.

      Warmly,
      Kori

  8. Sofie
    | Reply

    What a fantastic site you have. Thanks a lot for the Indigo vat description. It is very extensive and absolutely perfect for me. Thanks!

  9. George
    | Reply

    Great post Thank you for sharing the details. Have some 50 plants various sizes some are ready some are not! From your 7 plants how much indigo powder did you manage to make? Have I over extended at 50? Thank you!

    • ecotone.threads@gmail.com
      | Reply

      Hi George,
      Pigment yield varies based on a number of different factors, which I will touch on in an upcoming post. As for whether or not you have overextended yourself with 50 plants, that is up to you! We grow hundreds of plants each year, it may simply come down to the time and resources you have available to you to process them all into pigment 🙂

      Best wishes,
      Kori

  10. Jovencio de la Paz
    | Reply

    Thank you for this wonderful article, I have used and referred to it many, many times!

    One quick question: this season the “pigment” sediment was not blue, but a deep green. What do you think has happened? I am referring to the sediment at the end of the “concentrate” step in the instructions. The last time we did this it was the correct blue shade.

    Any help with this would be greatly appreciated!

  11. George
    | Reply

    Me too consistency of color is hard to keep. I have various shades of blue from midnight to some with a greenish hue? I wondered if perhaps it had something to do with the lime as revwashing encourages the indigo sediment to change color. I’ve been washing sediment three times but some batches ( 4-6lbs of plant matter per batch ) which are greenish do look bluer with a 4th or 5th wash through with hot water. Also noted age of lime can effect color. Kori what say you ?

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