Indigo, deep blue dye from the Indigofera tinctoria plant, often associated with blue denim, is one of humanity's oldest dyes. The leaves of the tropical shrub contain indican, a brilliant blue pigment. A chemical compound, it can be transformed into brilliant indigo dye.
Indigofera tinctoria is a flowering plant native to tropical and subtropical regions. It enjoys warm climates and is prized for its leaves, which contain indican, a chemical compound. Processed, indican converts to indigo dye. Extracting dye is based on traditional methods.
In medieval times indigo has its own trade network. The indigo trade routes move the dye or fabric to China and Vietnam from India. Central Asia receives it from China.
Uzbekistan in Central Asia also obtains it via Persia, from where it moves to Egypt. Overland trade routes of the 17th century include Agra to Lahore and Surat; Lahore to Kabul and Middle East and further; and Sind to Lahore.
1. Harvesting the Indigo Plant
Selecting leaves at the moment the indican concentration is optimal is crucial to ensuring a vibrant dye. To extract the best dye, the artisan should harvest the indigo plant when it's fully mature. This is late summer or early fall, when leaves are lush and green.
Indigo is widespread in tropical and subtropical regions. Using garden scissors or shears, carefully cut the leaves from the stems. Do not denude the plants but it's wise to gather enough leaves for a decent amount of dye. 1-2 pounds (453 - 987 g) of fresh leaves is good.
2. Soaking the Leaves:
Once the leaves are harvested, they must be soaked in water to extract the dye.
Fill a large container with warm water.
Submerge the leaves, ensuring they are fully covered.
Allow the mixture to steep for 24 hours. This helps to release the indican from the leaves into the water.
3. Fermentation
After soaking, the time comes to ferment the mixture.
Strain the leaves out of the water using a fine mesh strainer or cheesecloth. A greenish liquid like alien juice will appear.
Keep this liquid in a covered container at room temperature. Over the next few days, natural fermentation will cause the mixture to develop a distinctive smell. Fermentation is crucial because it converts indican into indoxyl, a precursor to the indigo dye itself.
Following fermentation, the mixture is exposed to oxygen, triggering oxidation of indoxyl into insoluble indigo particles. The stirring of the solution is a critical step in ensuring the even dispersion of the dye.
4. Behold the Precipitate
After a few days of fermentation a blue precipitate forms at the bottom of the container. Insoluble indigo particles settle at the bottom of the solution. The liquid is then decanted, leaving behind a concentrated paste of indigo pigment.
5. ... and Separate
Carefully pour off the top liquid without disturbing the sediment. This might require diligence and/or a separatory funnel.
Add fresh water to the sediment and stir gently to dissolve it.
Allow the mixture to sit undisturbed for a while until the indigo settles again.
Unlike synthetic dyes, natural indigo is biodegradable and eco-friendly.
6. Drying the Indigo
To store indigo dye, dry it for future use.
Spread the paste on a tray or parchment paper in a well-ventilated area away from direct sunlight.
Allow it to dry completely until it forms a powder. It can be ground into a finer powder as desired.
Dyeing with Natural Indigo
Prepare the Fabric:
Wash fabric to remove any dirt. Soak it in a fixative (mordant) solution, such as an aqua mix of ferrous sulfate (iron(II) sulfate) or alum (potassium sulfate). This helps dye bond with fabric. Do not use vinegar or table salt NaCl, they don't work. The salts used must be metal salts.
Other than metal salts tannins can be used, for example oak gall extracts. This can darken the material which may or may not work well, depending on the shade. In one ancient recipe, camel urine is recommended as a mordant. More about mordants here.
Dye Process:
Submerge the fabric in the indigo dye bath.
Allow it to soak until the fabric reaches the desired intensity of shade. The color will appear green when wet and will become blue as it oxidizes.
Rinse in cold water and hang to dry.
Repeat if necessary.
Extracting dye or pigment from the indigo plant, Indigofera tinctoria, can be an enjoyable experience connecting with nature and ancient traditions. The process requires patience and care and if at first success is elusive, persistence pays off.
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