The rebellious child of the natural dye world: indigo. We always have to distinguish it from others and handle it on its own. We will do so again in this article.
We can easily come across color blue or blue-purple in nature. In our first natural dyeing trials, fruits, roots, seeds, and leaves that are rich in anthocyanins such as purple cabbage, black carrots, black beans, purple basil, and black mulberry excite us first and then sadden us. Been there. Because anthocyanins are very sensitive to both pH and light, you lose your color, especially in cellulosic fibers such as cotton, in the first wash, or in light in a short time. At this point, the only blue that will give us satisfactory results is indigo.
Indigo is the name of the plant that contains the most amount of indigo dye, but it is also the name of the compound that gives us the blue color. Various plants contain the indican compound which is the precursor to indigo in their leaves. Indican is a colorless, water-soluble amino acid derivative. As a result of the fermenting of the leaves in water, the indican first turns into indoxyl, and as a result of the contact of indoxyl with oxygen, indigotin is formed. Indigotin precipitates as blue particles that are insoluble in water. This is what we use as a powder indigo dye. It is obtained by fermenting the leaves.
The plant containing the highest concentration of indigo precursor indican in its leaves is the Indigofera tinctoria plant, which we call indigo. Its habitat is South Asia, especially India. As a matter of fact, the word indigo is derived from the Latin ‘indicum’ and means 'from India'. However, there are other plants that live on different continents and contain indican. The woad, Isatis tinctoria, which is also found in Turkey and spread to the European continent, is one of them. On the map below, you can see examples of plants containing indigo classified according to their dominant regions.
When we look at the history of the Indigo, we see that it is one of the oldest dyes of humanity. The oldest evidence that we come across are textile products dyed with indigo is around 2000 BC, Egypt. Indigo dyeing appears as blue stripes on the edges of linen woven fabrics in which the pharaoh mummies were wrapped. We know that since the 1st century BC, it started to be cultivated in its homeland Southeast Asia, especially in India. India has been famous for its textile products from ancient times and these products were transported elsewhere via the Silk Road and other trade routes. In ancient Greek and Rome, textiles dyed with indigo were also very popular, but in the region, woad was used to obtain indigo. The woad gave the same precious blue, and it was on hand, but it was more troublesome to obtain the dyestuff, as the indigotin compound was found in lower concentrations in the leaves.
When we come to more recent history, we see that the maritime trade routes between Europe and Asia make it easier to reach quality indigo, and Britain, which dominates India, has benefited from European indigo imports, as well as using dyestuff in the developing clothing industry. After Napoleon put an embargo on British imports and encouraged the French to produce woad for army uniforms, woad production in Europe was revived. Two events that took place towards the end of the 19th century were very influential in the history of indigo.
The first of these was that Jacob Davis and Levi Strauss & Co. in 1873 patented workwear from indigo dyed blue blue jeans reinforced with metal rivets to market the sturdy suit that farmers, workers and cowboys needed. The distinctive pale blue color that the blue jean fabric has acquired over time has turned into a fashion style. The other was that Adolf von Baeyer produced indigo synthetically in 1897. Instead of the natural indigo, its synthetic version is now used to a large extent. Its natural production is done on a small scale, especially in India and Africa. The indigo you buy from us is produced by an organic certified manufacturer in India. Shop link is here.
Now that we have some idea of what the Indigo is and its history, let's move on to how we can dye with it.
Indigo dye in powder form obtained by fermentation from the leaves of the Indigofera tinctoria (indigo) plant is the inactive form of the dye. We need to transform it into its active form through a series of reactions. This process is traditionally done in vats, so indigo dyeing is also called vat dyeing. In vat dyeing, it is not necessary to apply mordant to the fabric. For more information on this subject, you can check our 'Getting Started to Natural Dyeing' article.
Although we will not mordant the fibers that we will dye with indigo, a good washing is essential for a homogeneous and permanent dyeing. For this purpose, cellulosic fibers such as cotton and linen are cleaned by boiling in washing soda, and protein fibers such as silk and wool are boiled with soap. It is dyed after rinsing thoroughly. It must be wet before dipping in the vat.
We need to start preparing the indigo vat by deciding in what size and amount we will do the dyeing. If our dyeing is only the size of a trial, or if it consists of small pieces, a small jar will do. Basically, the size of our dye vat is determined by the size of the material we will dye; it must be able to enter vat without getting stuck.
The second thing we will decide on is how much dye we will use. For indigo dyeing, we recommend that you abandon the idea of getting light blues for permanent results. Although it is possible to achieve this result by using less dye and making short-term dips, this situation decreases the dyeing quality very much and affects the permanence of the color negatively. Therefore, the healthiest results with indigo are the dark blues you will get with sufficient amount of dye and multiple dips. By sufficient amount we mean not using less than 10g of dye in vats up to 5 liters. We can say that 20g is ideal. As the volume of your vat increases, you should increase this amount because the amount of fiber you will dye increases in the same proportion.
Indigo in blue powder form is in inactive form as we mentioned before. In other words, it has no dyeing quality, only stains. To convert it into active form, we need to dissolve it in water and then 'reduce' it. Since we don't want to drown you in the chemistry of the work, we won't go into the details of this reaction, just talk about its logic. The sequence of actions should be as follows:
Soaking indigo > adding reducing agent > raising pH > waiting to reduce > dyeing
If you drop a few drops of water on the indigo powder, you will see that these droplets roll over the indigo powder instead of being absorbed by it. In other words, we need to establish the relation of indigo powder with water. For this, you can put indigo in a jar with hot water (around 50-60 degrees Celsius) and glass balls and shake them. Or, you can make an indigo paste with a small amount of hot water in a porcelain mortar. As another method, you can mix indigo and hot water thoroughly with a hand blender. If you can't do any of these, you have to make sure you mix it very well with water. Then pour this mixture in a 1 liter jar (min.) and add water, keeping in mind that you will add more substances later. We will add our reducing agent to the jar first.
You can come across to many recipes that uses several different materials to reduce indigo. We use the 1-2-3 vat, which we think is the most practical and effective. So it is 1 part indigo, 2 parts pH regulator, 3 parts reducing agent. Considering we are using 20g of indigo, this will do 60g of reducing agent. Here we use fructose, or fruit sugar, as a reducing agent. Shop link is here. Add the appropriate amount of fructose to the jar and mix well. However, this alone is not enough to initiate the reduction reaction because the indigo particles are still undissolved and are suspended in water.
In order to make the indigo soluble, we need to raise the pH of the vat. For this, we use 2 parts calcium hydroxide, ie slaked lime. Considering we use 20g of indigo, this will make 40g of calcium hydroxide. Add to jar and mix well. At this stage, some chemical reactions may occur in the environment, do not worry. If you need to top it up with water, add some water and let the solution rest. Seeing a bronze layer on the surface of the solution over time indicates that things are on track.
This jar can be your vat if it is enough. Make sure you wait at least 6h for this. But if you need a larger volume, you should transfer the dye solution from the jar to a larger container. For this, fill your bucket with hot water (around 50-60 degrees Celsius) and pour the solution in the jar slowly, without bubbles, into the bucket as low as possible. Mix quickly, in one direction, without shaking. From this point on, we need to get as little oxygen as possible into the dye vat. So your movements should be rapid, but gentle and careful. The dye vat should wait one night and the dyeing should be done the next day. If the vat is mixed for a few times in this period without shaking, a better result will be obtained from the dye since the indigo particles that have settled to the bottom will be reintroduced into the environment.
The most characteristic feature of indigo dyeing is that the blue inactive solution takes a yellow-green color and turns into the active form. Therefore, if the color of your fiber changes from green to blue as a result of contact with oxygen after you dip and remove the fiber from the vat, your dyeing is successful. The dyeing function of indigo is by covering the fiber (in mordant dyes this is penetrating). For this reason, the shade of the color is determined by how many dips you make in the vat. More dipping means more coats, which means darker blue. It is enough to keep it for 5-10 minutes for each dip in the vat.
After you have finished your dyeing, you need to neutralize your fiber. Your dye vat was a fairly alkaline environment. Although cotton is relatively durable, animal fibers suffer from high pH. Therefore, we need a low pH, an acid, for neutralization. White vinegar is ideal for this job. First, rinse the fiber you have finished dyeing under running water, then soak it in vinegar water for at least half an hour. Finally, wash with hot water and natural soap.
Congratulations, you have done your first indigo dyeing. For more detailed info, please see our Indigo Dyeing Kit page here, it is a perfect way to start your own vat.
Scanned images from the book 'Indigo, Egyptian Mummies to Blue Jeans', by Jenny Balfour-Paul