It is one thing to put all the ingredients in a “vat” and hope for the best result: a reduced vat that will dye beautiful blues. It is a whole other thing to understand what happens in that vat. I am not a scientist, but the following is some of what I have learned from Dr. Kim Borges, biochemistry professor at Warren Wilson College in Swannanoa, NC. Dr. Borges uses indigo fermentation with her class to help students understand the basic concepts of bacterial fermentation.
She states that “how the indigo reduction happens in the fermentation vat seems to be the big, unresolved question in the microbiology research world.”
The quick reduction vat (made with fructose, iron, etc.) requires very high pH. The glucose (and/or a degradation product of glucose that is made at high pH) appears to donate electrons to the indigo molecules directly.
In the fermentation vats, the concentration of free glucose is much lower. Many different microbes use glucose as a preferred fuel. It is suspected that much of the free glucose will be taken up by community microbes before it reduces indigo, though that is a guess. It is likely that cellulose, starch, arabinoxylans and other complex carbohydrates from wheat bran (and from other plant materials) are converted to simple sugars by some of the microbes in the community. But those microbes will shuttle most of the sugar into their cells for their own use, and so only some of the easily metabolizable sugars like glucose will stay in the fermentation fluid.
It’s interesting that most kinds of bacteria can’t degrade those complex carbohydrates – only certain microbes specialize in that activity. A functioning sukumo-based vat has Amphibacillus and Alkalibacterium, which are types of bacteria that degrade wheat bran carbohydrates to produce lactic acid as waste. Other kinds of bacteria seem to be able to use the lactic acid, which helps to keep the pH from falling too much.
I think that one reason we stir the vat daily is to disperse the “pockets” of lactic acid that build up around the wheat bran fermenters and move it to the lactic acid users before the vat spoils. A network of microbes based upon use of hard-to digest complex carbohydrates will develop in a good vat. And somehow some of these microbes transfer electrons from proteins on the outside of their cells to indigo particles (probably carried by anthraquinones and other electron-carrying small molecules). There is still so much to learn!
Regarding the addition of sake (rice wine) or glucose (malt syrup, rice extract, etc.) to the sukumo vat: It doesn’t seem like the sake adds enough alcohol to kill bacteria that would de-rail the indigo reduction and spoil the vat. Perhaps those added sugars initially provide easy to metabolize “fuel” that starts the development of the bacterial community. The bacteria that dominate the sukumo vat initially don’t seem to be indigo reducers. But they do seem to be good at using up oxygen to create the anaerobic conditions preferred by indigo reducers. Maybe the added sugar helps to cultivate them, and it is worth testing.
As an aside: Rowland Ricketts once told me that he never saw a traditional Japanese dyer use sake in the vat. It is much better to drink it!
This recipe can used to make a 1-liter vat or can be scaled up to a larger vat. I typically make a vat that is 50 liters in volume. The recipe is intended as a starting point for the dyer who wishes to explore fermentation.
Observe carefully. Be flexible. Experiment. Keep records!
As stated earlier, pleasestart with a small vat of 1-4 liters. Get comfortable with it and wait for reduction. Any successful test vat can be added to a larger vat, speeding up the fermentation/reduction time for the new vat. So, small vats are useful.
Ingredients:
Indigo pigment: 2-10 grams per liter (see note #1 below)
Dried and ground Indigofera tinctoria leaves: 5 grams per liter (see note #2 below)
OR
Ground, “spent” madder root: 5 grams per liter. (see note #3 below)
Wheat bran: 5 grams per liter. I typically use “feed-grade” bran sourced from my local farm supply store.
Soda ash (sodium carbonate) OR potash (potassium hydroxide): 25 grams per liter. Either soda ash or potash is effective. (see note #4 below)
Optional: If you have them: dried woad balls/patties or dried polygonum leaves etc., crushed: 5 grams per liter. (see note #5 below)
Note #1: Deciding how much indigo pigment to put into a vat is a complex decision and largely based on:
The size of the vat
The amount of dyeing that will be done in the vat and the size of the dyeable goods
The type of textiles that will be dyed: yardage requires much more volume that yarn.
How long the vat is expected to last.
The fermented vat seems to be very efficient at reducing the indigo available in the vat. I have observed that a vat with 2 grams of indigo pigment/liter can produce a blue that is almost identical to one with 8 grams per liter, but the vat with the smaller amount of indigo will not last as long. Fermented vats will result in pale colors only after much of the indigo has been used up and the vat becomes weaker. My 50-liter vat with 2 grams of indigo per liter took over 20 months to reach a point where it produced pale blues.
I have never added additional indigo to a vat. I have always felt that when a vat was “finished” it was time to start fresh again, although that might be something to consider.
“WEAK” vat using 2 grams indigo per liter. Sample taken 2 weeks after making vat“STRONG” vat using 8 grams indigoer liter. Sample taken 2 weeks after making vat
Although the vat on the right uses 4x the amount of indigo pigment, and the the vats were equally reduced, they are close to identical in depth of shade.
Vats that are kept a long time will build up solid materials on the bottom: mostly lime and wheat bran. When stirring the vat, there is noticeably more “stuff” on the bottom. I suspect that I have kept vats longer than might be recommended – I guess I may not be dyeing enough!
For all the above reasons, I would recommend using a smaller amount of indigo pigment in the vat. Use it up. Dye some pale colors and mix a new one. Ideally, the studio will have two vats: an old vat for pale colors and another for darker colors.
Note #2: “Spent” madder has already been used for dyeing red. The alizarin and other dye components in the roots are not necessary for the fermentation.
When dyeing with madder root, I place the ground roots into a fine mesh bag that is large enough for the dyestuff to move freely. When the red dyeing is completed, I remove the ground root from the bag and dry it. It will dry easily on a tray if left in the open air. Once completely dry, the madder can be stored until it is needed for an indigo vat. Madder that has not already be used for dyeing red can be used but it would a waste of a good red dye. Traditionally, the madder dyers would sell their spent madder root to the indigo dyers.
Note #3: Dried and ground Indigofera tinctoria leaves are often sold as “black henna” and used, in combination with madder, to dye hair black. I source mine from Maiwa.
Note #4:The stated quantity of soda ash or potash is ideal to achieve the desired pH (12.0) using MY WATER, which is acidic (pH 6). If your water is neutral, less soda ash might be required.
Note #5: When I have fresh indigo of any variety in the garden, I will grind up the leaves, form them into small “patties” and dry them. The theory is that these will introduce supplemental bacteria to the vat. When I use them, my vats tend to reduce a little bit faster. If you do not have fresh indigo to make these, that is just fine.
Indigo leaf patties, made from fresh indigo leaves (left). They are dried to preserve (right) and can be added to feed the vat and to boost fermentation. I have used all types of indigo leaves from my garden for this: Persicaria tinctoria, Indigofera suffruticosa, and Isatis tinctoria.
Procedure:
Thoroughly hydrate the indigo pigment in water unless you are using paste pigment.
Boil the bran in a small amount of water for about 10 minutes. It should become the consistency of cooked cereal and emit a slightly sweet odor. Cool before use, until just warm.
Prepare the “food” for the vat:
If using madder root, cook this briefly. It can be added to the bran and they can be cooked together for efficiency.
If using ground Indigofera tinctoria leaves, stir them into warm water to make a smooth, watery paste.
If using dried indigo patties, crush them up before adding to the vat
Dissolve the soda ash or potash in boiling water. Cool before use until just warm.
Add warm water to the dye vessel until it is approximately ¾ full.
Add the remainder of the ingredients to the dye vessel.
Wait a few days, to add the liquid to full capacity.
Stir the vat carefully with a circular, centrifugal motion. Cover the vat loosely.
Warm the vat, if required. Optimal temperature for bacteria growth is 30°C/86°F but it can grow between the temperatures of 10-50°C/50-122°F. Bacterial growth decreases at temperatures greater than 36°C/96.8°F
Measure the pH. It should be in the range of 10-11. Once the vat is at full capacity, add a very small amount of lime, (calcium hydroxide) and re-test the pH.
Stir the vat in a centrifugal motion 2-3 times a day.
Monitor the pH – A good pH meter is an excellent investment. Alternatively, use pH papers that have multiple indicator zones.
As the fermentation begins, lactic acid will be created, and the pH of the vat will fall. This is the time to completely fill your vat using warm water into which you have dissolved soda ash or potash (25 grams per liter).
Measure the pH It should be in the range of 9.5-11. Once the vat is at full capacity, test the pH and record this.
Add a very small amount of lime (calcium hydroxide), if necessary. Lime is a much more concentrated “fix” for pH adjustments.
Watch for the vat to form an iridescent film on the surface. This is an indication that fermentation and reduction has begun.
Smell the vat. As bacteria causes the fermentation of the vat, the “odor” will be an indicator of activity.
Concurrently, test the color: the best way to tell if the vat is reduced, is to test its ability to dye.
Starting on day two, begin test dyeing. Place a small piece of wetted-out cotton cloth into the vat for 10 minutes. Observe and note the results. Continue to test the vat each day, maintaining a record of the dye tests.
Once the test fabric dyes a clear blue color, the vat is ready to use for dyeing. Usually this takes about 8-14 days.
Dedicate a small notebook to each vat that you build so that the vat can be observed over weeks/months. Place the dyed samples in your notebook. This will be an important resource tool to understanding your vat.
Once reduced, the vat can be monitored by weekly testing.
From this point, follow the instructions in “Vat Maintenance” post, which will follow.
Day 1 – Day 13 of two vats made with madder root. One was made with “spent” root, the other was made with root that had not been used for dyeing. (I knew that they would both work, but sometimes I just need to prove it to myself!)
By day 6 the pH had begun to drop. The lack of color on that day is a great indicator that something is out of balance – and most likely it is the pH. A small amount of lime was added to both vats, and the color improved.
The same drop in pH happened on day 9. This illustrates how easy it is to read the condition of your vat from dyed samples. After day 13, I began using these vat for dyeing.
A similar test using spent dock root (Rumex crispus) and rhubarb root (Rheum palmatum). Reduction came more quickly in these vats. Perhaps this is because the plant material was a finer ground powder and more easily accessed by the vat. I source dock and rhubarb that are prepared for medicinal purposes.
This decision is primarily based on your intended use of the vat. If the vat is made for only small scale test dyeing, perhaps a 1-liter jar is adequate. Larger test dyeing and the dyeing of small pieces can likely be done in a 5-gallon bucket (approximately 18 liters). If you wish to dye garments, multiple skeins of yarn, or fabrics, I think the minimum size for good dyeing is approximately 50 liters.
Importantly, undissolved materials (lime, bran, etc.) will build up over time in the bottom of the vat, leaving only the upper portion of the vat available for dyeing. Fourteen gallon plastic drums can be sourced, from a variety of suppliers, which are significantly taller than they are wide, allowing plenty of room at the top of the vat for good dyeing, while allowing the solid materials to settle to the bottom half of the vessel.
Three 14 gallon drum for indigo vats. Two of the vats are wrapped in a bucket heater band
It is highly recommended that the dyer who is new to the use of fermented indigo vats begin with small (one liter) test vats to become familiar with and confident with the process before moving on to a large vat.
Once successfully reduced, test vat(s) can be used to “seed” a larger vat when you are ready to build one for serious dyeing. “Seeding” a larger vat in this way will stimulate bacteria growth and can significantly decrease the time required for the larger vat to reduce.
Small test vats can also be added to older vats that have decreased in volume from evaporation or just the process of dyeing.
My dye studio frequently has indigo testing going on, as I compare variations of the vats. Note that some of the vats are wrapped in heating pads in order to stimulate fermentation.
Water:
It’s important to consider the source of your water. Is it acidic? neutral? City water may have chlorine incorporated, which will inhibit the growth of bacteria needed for the vat. The amount of chlorine can be influenced by the distance from the chlorination facility as chlorine will dissipate. If your water is chlorinated or smells of chlorine, there are three ways that can be used to remove it:
• Boil the water for 15 minutes to release the chlorine.
• Leave the water in an open container at room temperature for 24 hours.
• The use of filtration systems can also be used to remove chlorine.
How long will it take for the vat to reduce and begin dyeing?
My vats will typically reduce and begin giving me a full, clear indigo blue after 7-14 days. But I have seen it take as long as 40 days! Much of this depends on how well the vat is tended; temperature, pH, etc. You will only learn the length of time required for the vat to be ready by making that vat and by careful monitoring and testing. Trust me. You will know when it’s ready. Your test strips will be blue!
How long will a fermented vat last?
The life of a vat depends on:
how much the vat is used for dyeing
how much indigo is in the vat
vat maintenance
organic matter in the vat
I have had fermented vats that lasted 3 years or longer, with careful monitoring and maintenance. Over time, though, the solids will build up at the bottom of the vat, decreasing the usable solution that is available for dyeing in the upper portion of the vat. For this reason, many dyers will plan to use a vat for about 6-12 months and then discard it. I usually dispose old vats on the compost pile, but, after neutralization, the liquids can be put down the drain but it’s best to strain out any solids on the bottom.
The amount of indigo pigment used when making the initial vat will determine how long the vat can be used for dyeing. Counterintuitively, a vat that has 2 grams of indigo per liter will initially result in nearly the same depth of blue dye as one with 8 grams of indigo. I know that this sounds illogical but I know this from observation. Importantly, the vat with the lesser amount of dye will weaken sooner, as the dye gets used up, and result in pale blue colors. This can be very desirable, as the ability to achieve a pale blue is sometimes important for controlled color mixing. For this reason, I would recommend using smaller amounts of indigo (2 grams per liter) when the vat is begun. As the vat becomes weaker and results in pale colors, start a second vat to produce darker shades.
Does the fermented vat require heat?
I have found that the vat does best with supplemental heat (between 16°C/60°F and 30°C/85°F) in the initial stage while fermentation is starting. If the ambient temperature in the dye studio is warm enough, there is no reason for added heat. If supplemental heat is required, it’s best to use a heater that will surround the vessel. Avoid immersion bucket heaters, which can get too hot very and concentrated high temperatures can kill the live bacteria. Some form of temperature control is ideal. A plastic covered household heating pad, set on low, will work well for small vats. For larger vats, a bucket wrap heater with a thermostat is ideal. For this reason I use a temperature controller with an immersible probe. This will automatically turn the heater on and off to maintain an ideal temperature.
Once fermentation has been established and the vat is in reduction, ideally, you would maintain those same temperatures. But, I have found that it is not always necessary to continue to apply supplemental heat to the vat. I have maintained fermented vats successfully through the winter where the overnight ambient temperature in the studio is as low as 5°C/42°F. One winter I had two vats with heat and another without heat. All vats continued to dye well. But there may be better penetration of fibers with a warmer vat.
What form of indigo is used for the fermented vat?
The vats described here are made with extracted indigo pigment. I prefer to use natural indigo pigment, but the vat can also be made successfully using synthetic pigment. I have had success using dried indigo pigment or indigo paste pigment (pigment that has been freshly extracted and never dried). I assume that paste pigment may still contain bacteria that will aid in the reduction of the vat which is, obviously, a plus.
What is the source of alkalinity for the fermented vat?
These vats can be successfully made using soda ash (sodium carbonate), potash (potassium carbonate) or wood ash lye, which is made from hardwood ashes. The processes of making wood ash lye will be described in a later blog post. From my research, it is suggested that soda ash or potash was typically used in European production workshops vats of the 18th and 19th century.
The maintenance of the vat requires the addition of very small amounts of lime (calcium hydroxide) to maintain the pH, since it is a much more potent alkaline substance.
What is the source of the bacteria used to reduce the fermented vat?
While composted sukumo is a source of indigo pigment, some of the bacteria, and of the plant material for bacterial growth, the vats made with extracted indigo pigment require additional organic material to begin and maintain the fermentation process.
• Wheat bran is a primary source of bacteria for the vat and is used for all fermented vats, including in the sukumo vat.
• In addition, the vat requires a source of “food” for the bacteria, which also contributes to the diversity of anaerobic bacteria in the vat.
• Traditional European dyers used “spent” madder root. This is finely ground madder root that has already been used for its red dye.
• Hisako Sumi, Japanese indigo dyer and researcher, recommends the use of dried indigofera tinctoria leaves as an alternative bacteria/food source for the vats. (I would speculate that these leaves also contain very small amounts of indigo precursors). The Indigofera tinctoria leaves are dried, finely ground and are often used for used as a dye for hair. The ground, dried leaves are sometimes referred to (and sold as) “black henna”, since a combination of henna and indigo powder will result in a natural black hair dye.
I have been successful using alternative plant materials and will go into that in more detail in a later blog post. Research and my own observation indicate that diverse sources of bacteria will help contribute to, and maintain, successful fermentation.
In addition to the madder root and/or dried indigofera tinctoria leaves used during the construction of the vat, other organic substances can be added to the vat and will contributes to the fermentation process and include:
Woad balls can be made by grinding fresh leaves of the Isatis tinctoria plant, forming the balls and drying. These balls can also be “couched” or lightly composted by breaking them apart, adding a bit of water, and allowing them to ferment.
Fresh leaves from Polygonum tinctorium or Indigofera sp. can be ground, formed into small “patties” and then dried. These also can be broken up and added to the vat.
Additional wheat bran is used on a regular basis to maintain fermentation throughout the life of the vat.
Does the fermented vat have an “odor”?
Yes! The vat has a distinct smell from the bacterial fermentation. The smell is also a useful indicator that the vat is “working”. This is not a sweet-smelling vat, such as a vat reduced with bananas or fructose. Personally, I do not find the odor unpleasant (once I got used to it!) but it is likely you will not want to keep this vat in a closed “living space” as you (or your housemate) may find it objectionable.
The NEXT post will have the first “instructions” for building a fermentation vat.
Fermentation is a biochemical process in which complex organic molecules are broken down into smaller molecules through the action of bacteria, yeasts, or other microorganisms.
In food production, it can broadly refer to any process in which the activity of microorganisms can bring about a desirable change to a foodstuff or beverage, such as the making of cheese, yogurt, sourdough bread, vinegar, fermented vegetables (pickles and kimchi), or beer, wine, or kombucha, in which sugars are transformed to alcohol.
In biochemistry (and specifically in indigo fermentation) fermentation is a process that occurs through the action of microbial enzymes under alkaline and anaerobic (in the absence of oxygen) conditions. The result is a reduction of the indigo dye molecule to make it soluble.
Many microorganisms and bacteria thrive in this unique alkaline/anaerobic environment. The most important are Alkalibacterium sp., which produces lactic acid as a biproduct. The lactic acid will also bring down the pH.
Many grains contain this lactic acid bacteria. When grains are dry, those bacteria are dormant. But when soaked in water (or an alkaline liquid as in the case of indigo) the bacteria become active and produces enzymes that are useful to the reduction process. Wheat bran is a substance in which the indigo reducing bacteria/organisms live. It is a key ingredient in the fermentation vat. Traditional recipes use wheat bran as an element of the vat, and it is added periodically to maintain the health of the fermented vat.
Sukumo is composted indigo (polygonum tinctorium) leaves. Though it might already contain some of the bacteria that are needed for fermentation, wheat bran is always added to this vat as well.
Extracted indigo pigment lacks the microorganisms necessary to initiate the fermentation. This is especially the case of any pigment that has been dried. Organic material MUST be added to the vat to stimulate and maintain fermentation. Since medieval times spent madder root (Rubia tinctorium) was added to the vat to maintain fermentation. This “spent” madder was a waste product from madder red dyeing after the roots had been used to extract the red dye. The fermentation delivers a constant supply of glucose by breaking down starches and celluloses from the organic matter (madder root).
Over the last few years, I have experimented with spent madder root and other organic substances to determine alternative plant materials that can be used in place of the madder root, or in addition to it. I have successfully used spent rhubarb root, dock root, and dried Indigofera tinctoria leaves.
Ground madder root, which has already been used for dyeing, dried in a shallow tray. It will be stored and ready for use in an indigo vat.
Dried, ground Indigofera tinctoria leaves (often sold as a dye for hair)
Some bacteria in the vat create lactic acid as a byproduct, which is a major reason for the decrease in pH that will naturally occur in the vat. For this reason, the pH of the vat must be carefully monitored and maintained on a regular basis. A fermented vat is a long-term investment. Be prepared to treat it as one and commit the time to monitor it by regular stirring, pH testing, feeding – and of course, dyeing in it!
Having a good pH meter on hand is very helpful (This is the one I have) but pH papers with multiple pads for enhanced accuracy can also work well.
Full range pH papers with multiple pads for measuring increases the accuracy.
For further reading: This is a sampling of scientific papers (with links) that discuss the bacterial process of fermented indigo vats.
In the early days of chemistry, oxidation was defined as a gaining of oxygen atoms, and reduction was a loss of oxygen atoms. Indigo was said to be reduced because it lost an oxygen atom.
In actuality, there is no loss or gain of the oxygen molecule. The molecule of the insoluble indigo pigment contains double bonds to oxygen. During reduction, that molecule gains 2 electrons and, as a result, the bonds to the oxygen molecule become single bonds, thus making it soluble. This soluble indigo is referred to as leucoindigo or “indigo white”. Leucoindigo is the water-soluble yellowish molecule that soaks into and dyes the textile. This is one of the grand “mysteries” of dyeing and chemistry!
Leucoindigo is visible as the characteristic yellowish color below the surface of some vats. The leuco color of fermentation vat is more green than yellow. Once a textile is immersed in the vat it come out of that vat with the leuco color (yellow or green). The textile will turn blue through exposure to oxygen.
What is Redox? Redox is a chemical reaction that takes place between an oxidizing substance and a reducing substance. The oxidizing substance loses electrons in the reaction, and the reducing substance gains electrons. These two things happen simultaneously, and one does not happen without the other
All indigo vats require a high alkalinity (high pH) for proper functioning. The plants, carbohydrates, sugars, or minerals used for the indigo vat are reductive, which means that they oxidize and give off electrons. In the alkaline environment of the vat, reduction is even stronger. The indigo molecule is forced to receive the two negatively charged electrons, which is a reduction; this influences the oxygen bonds of the indigo pigment, making the indigo molecule attractive to the positively charged portion of the water molecule. In this way the indigo becomes soluble (leucoindigo). Once it is soluble, the dye can penetrate the textile. After dyeing, oxidation (exposure to air) will once again make the indigo insoluble in the textile.
Leuco color from fructose vatOxidized color from fructose vatLeuco color from fermentation vatOxidized color from fermentation vat
Fermentation vats are the oldest method of reducing indigo. These vats rely on the effect of bacteria present in an alkaline environment to cause the reduction that will allow the indigo molecule to become soluble. The bacteria existing in an oxygen-free environment is referred to as anaerobic. An indigo vat is reduced in anaerobic conditions.
A “sukumo” vat, traditional in Japan, is a fermented vat that uses composted indigo leaves from the polygonum tinctorium plant as a source of the dye plus cellulose plant material that will help feed the vat. A sukumo vat contains no added indigo pigment. The preparation of sukumo is a lengthy process requiring the composting of indigo leaves after they have been harvested and carefully air dried.
Dried Persicaria tinctoria leavesComposted sukumo, the result of composting the dried leaves. Photo by Debbie Ketchum Jircik of her “home made” small batch sukumo.
For those of us who do not have access to sukumo, it is important to know that a fermented vat can also be made using indigo pigment. This is the approach that was often used by 18th century commercial dye workshops in Europe. Since the pigment is inert, suitable sources of bacteria and “food” for that bacteria must be added to the vat.
• Advantages of the fermented vat: A fermented vat uses a lower pH (9.5-11) versus the quick reduction vats, which makes it suitable for both protein and cellulose fibers. The correct pH of a fermentation vat can be obtained using wood ash lye, soda ash, or potash. Only small amounts of lime are used throughout the life of the vat to maintain a correct pH. These vats are suitable for long-term use, provided they are maintained correctly. That is something that will be covered.
• Challenges of the fermented vat: Typically, the vat requires 7 -14 days to reach full reduction, but I have seen it take as long as 30 days. The vats must be carefully monitored and maintained by making regular additions of lime and organic material to maintain appropriate pH levels and insure a continuous source of bacteria.
Quick Reduction vats, though used historically, were re-introduced to contemporary dyers by Michel Garcia and have gained great popularity amongst contemporary practitioners. These are the vats that we presented in The Art and Science of Natural Dyeing. They are easy to make. They rely on the use of sugars, fruits, plants, or minerals and require a very alkaline environment (pH 11-13) to achieve reduction. This high pH necessitates the use of significant amounts of lime (calcium hydroxide) as an alkali.
• Advantages: These vats reduce quickly – usually in a day (or less). They use no harmful chemicals, though they do require working with a very alkaline substance and solution. Vats made with reducing sugars can be kept for several weeks and, with careful and regular maintenance, can be used for several months.
• Challenges: The high pH is not suitable for all fibers (a high pH will damage protein). The large quantity of lime (calcium hydroxide) used to achieve the pH builds up quickly in the vat. The lime is also very difficult to remove from the finished textile and can compromise the dye and color, possibly resulting in “unexplained” fading of the blue.
Chemical Vats use either sodium hydrosulfite or thiourea dioxide to reduce the indigo molecule. This process is used extensively in industry, and I know that some hand dyers also use this process, as it is very predictable.
• Advantages: Complete reduction takes place very quickly – usually within minutes. The pH of the vat is 10-11.
• Challenges: Reduction chemicals can potentially have a very detrimental effect on the lungs and health of the dyer. When used in combination with a high pH, they can also damage the tactile qualities of wool fibers. Personally, I do not like the smell of the chemicals.
Because reduction is so complete using reduction chemicals, it can be challenging to achieve pale colors when using chemical reduction. It is also difficult to use multiple immersions in the vat to increase the depth of shade, as repeated immersions will re-dissolve the indigo already incorporated in the textile.
On this blog site, I have previously written about the indigo fermentation vats in very general terms. I have been using these fermentation vats exclusively for over 5 years now and I feel strongly that it is the best approach to use for indigo dyeing. So, I have made the decision that I would like to share much more specific information regarding how to make and maintain these vats through a series of posts in coming weeks. I hope to roll a new one out every few days days or so.
Since I began the transition to using ONLY natural dyes in 2008, I have continued to learn and to refine my practice. Dyeing with indigo has been one of the most rewarding, yet challenging adventures. Striving for, and practicing a level of mastery related to indigo dyeing, is necessary to achieve a full palette of color using natural dyes and having the ability to control shades of indigo blue is a necessary skill.
In the 1970s, I did my first indigo dyeing using sodium hydrosulfite as a reduction agent for my vat. I never liked dealing with the reducing chemicals, such as sodium hydrosulfite or thiourea dioxide. The smell was off-putting and, more importantly, I had concerns regarding the safety of such chemicals. I abandoned their use (and indigo dyeing) until many years later.
I was thrilled when I learned from Michel Garcia that indigo vats could be made using benign substances such as sugars, plants, ferrous sulfate, and lime (calcium hydroxide) which I was able to purchase in the grocery store as “pickling lime”. Vats made this way are considered to be, or described as, “quick reduction” vats. They reduce and are ready for dyeing within hours and can be maintained for an extended period with proper attention. I was very happy. These are the vats that Joy and I included in our book “The Art and Science of Natural Dyes”. I believe that these are still the best vats for short term dyeing workshops and other situations where a working vat is required quickly.
Over time, though, I observed that there are issues and challenges with these vats.
Crocking (the rubbing off of color) was a problem, despite proper finishing and washing, and especially when dealing with knitting or weaving yarns, which are handled a great deal. All indigo dye seems to exhibit poor resistance to rubbing to some extent, but the quick reduction vats seems to crock more. What I understand is that excess calcium may react with the reduced indigo and makes it into insoluble compound. These vats depend on the use of large quantities of calcium (calcium hydroxide). I am now thinking that it is possibly the reason for the bad rubbing fastness or crocking.
This shows the “fading” which occurred on the folded cotton cloth that was stored in a dark place for a number of months. The indigo blue has nearly disappeared in some places. The fading mirrors the actual folds that were in the cloth. It is NOT an intentional design element.
The color often faded inexplicably, turning pale and displaying washed out areas, or just completely disappearing. I have observed this occurred where cloth was folded and put away on the shelf. Even when a textile was rolled up and stored in the dark, I would find that the blue had literally disappeared in some parts of a textile despite careful finishing and neutralization. I’ve had discussions with other dyers who have also experienced this same phenomenon, so I know I am not the only one who took note. I always do lightfast test on the dyes that I choose to use for my work but this was something else entirely
The “lime cycle” illustrates how limestone is heated to create quicklime. Water is added to make slaked lime. Does exposure to air/carbon dioxide turn the lime back into limestone again?
In 2017 I began my journey using indigo vats that reduce by the activity of fermentation after meeting Hisako Sumi, Japanese indigo dyer and researcher. Hisako encouraged me, guided me, and even put together and gifted me a small “kit” which she mailed from Japan, so that I could start my first fermented vat. I began experimenting, testing, dyeing, observing, and never looked back. Hisako generously ‘coached” and mentored me from from her home in in Hokkaido and provided me with a much deeper understanding of my vats.
The COVID pandemic kept many of us home for long stretches of time, and during that period many of us learned new skills or honed old ones. That time provided me the opportunity and focus to tend indigo vats and to develop and refine an understanding of the fermentation process. My indigo dyed textiles have never been better! I no longer fret over potential “unexplained” fading. The quick fermentation vats require high alkalinity (pH 12). The fermented vats are able to be maintained at a lower pH than the quick reduction vats (pH 9.5-11). This is accomplished by the use of wood ash lye, soda ash, OR potash to achieve the correct pH. I have used all of these alkaline sources successfully. Lime (calcium hydroxide) is used in very small amounts and only to “tweak” the pH maintain desired levels. The lower alkalinity of the fermented vats is more suitable for all fibers. I will likely never return to quick reduction vats, unless specific circumstances require their use.
In some of my previous blog posts, I have written about this process in general terms and also have given credit to Cheryl Kolander, whose online recipe was a good starting point for me, but until this time, I was not ready to publish anything definitive of my own. In fact, I have never published an “actual” recipe on my blog: Natural Dye: Experiments and Results.
I am not a trained scientist/chemist, but through experimenting and multiple observations I have done my best to understand what happens in the fermented indigo vat so that I can use and maintain the vat. And now it is time to share that specific information and information about the process I have used. Over the coming weeks (and about a dozen blog posts) I hope to “walk through” the planning/making/maintaining of a fermented vat and to encourage and guide dyers to explore on their own. And, as we approach summer in the northern hemisphere, it is a good time to try these vats. But do keep in mind, fermentation vats may not be the best for a beginning dyer or for someone who does not have the time and focus for it.
One does not do this alone. I owe much to Hisako Sumi, Michel Garcia, Joy Boutrup, Dr. Kim Borges of Warren Wilson College, and to all my colleagues and students who have been willing to experiment with me.
As a dyeing community, perhaps we can all help each other to learn, understand, and to work through the process of indigo fermentation. Your comments are most welcome. My goal is to start that process with a series of blog posts that might help you begin your own journey. By all means, if you have a “dye mentor”, do consult them! I don’t have all the answers but maybe we can get there together.
Last year, I made the decision to stop travel/teaching. It’s been a long journey since my first weaving in 1970, my first dyeing in 1972, my first teaching in 1976 and my committment to natural dye in 2008. This year I will turn 74 years old. I am also a grandmother for the first time and am actively involved in the unfolding life of a 18 month old little boy (who makes us smile every day).
What I have not done, is to stop learning, exploring, or asking questions about natural dye, dyeing, weaving, and/or how they might combine. Slowing some things down in my life is giving me to time to think more deeply about others, particularly indigo fermentation.
“Lessons”, a queen size quilt by Catharine Ellis using early woven shibori samples. Border fabric has been dyed with indigo using a fermentation vat.
Some time ago, Joy Boutrup and I discussed the possibility of another dye book that would expand what we presented in The Art and Science of Natural Dyes (Schiffer, 2019). While contemplating this dilemma, I came across the following quote from Annie Dillard:
“One of the things I know about writing is this: spend it all, shoot it, play it, lose it, all, right away, every time. Do not hoard what seems good for a later place in the book or for another book; give it, give it all, give it now. The impulse to save something good for a better place later is the signal to spend it now. Something more will arise for later, something better. These things fill from behind, from beneath, like well water. Similarly, the impulse to keep to yourself what you have learned is not only shameful, it is destructive. Anything you do not give freely and abundantly becomes lost to you. You open your safe and find ashes.”
Annie Dillard
So now, Joy and I have together made the decision that I would share the information I have learned using blogposts, instead of writing another book. Through a number of upcoming posts, I will discuss the process of indigo fermentation vats, the experiments I have done, and what I have learned about making, maintaining, and dyeing in those vats. I will explain, to the best of my ability, what is happening in those vats and why. Hopefully, this will encourage more of you to try fermented indigo vats and will provide enough information for a high likelihood of success. Each post will contain a link to a downloadable pdf version, which you are welcome to print and kept for studio reference. I would ask that you be respectful of this information though you are most welcome to share the link to my blog for reference.
Natural Dye: Experiments and Results 