• TOP UP THE VAT WITH BOILING WATER. When your vat liquid level starts to drop, top up your vat to full using boiling water. Boiling water contains essentially no dissolved gasses and is easier to reduce. Keeping your vat as full as possible helps to keep conditions properly reduced as the air pocket between the top surface of the liquid and the lid of the vat is smaller, allowing for less gas exchange.
MORE THAN ALL YOU NEED TO KNOW TO MAKE YOUR OWN INDIGO DYE VAT
Each dip accumulates more pigment on the fabric. This stepped cloth shows the saturation from 0-10 dips in an Iron Vat.
A NOTE FOR BEGINNERS
If this is your first foray into the world of indigo dyeing, I recommend starting with a kit. Though the step by step, detailed instructions that follow can certainly be followed by beginners, for ease, convenience and potential for less frustration, an all-in-one kit can’t be beat. I recommend my own natural indigo kit, but really, any (whether synthetic or natural) will help to familiarize you with the concepts and process of working with indigo. Thank you for humoring my plug, on to the info!
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SKIP AHEAD FOR INSTRUCTIONS, MATERIALS AND NOTES ON BOTH
T.M.I to follow regarding Indigo’s plant origins, the nature of the pigment and a bit of Vat chemistry.
Indigo pigment is produced within the leaves of a broad range of plants across an array of genera. They have been historically grown on different parts of the earth that suit their particular needs (sun, moisture, soil, etc). Varieties range from Indigofera Suffruticosa in Central America, Persicaria Tinctoria in Asia, Isatis Tinctoria throughout Northern Europe and Indigofera Tinctoria primarily in South and Southeast Asia. I grow and have extra seed for each of these varieties, please get in touch if you are interested in growing any of them. You can certainly find a variety that you could grow in your local climate.
These plants each contain only a small percentage by weight of actual dyestuff in their leaves. It can take tons of plant material to make a few pounds of dyestuff. One way or another, the pigment is extracted from the leaves and can be purchased in a concentrated pasted, dried powder, ball or brick form. This indigo concentrate is often graded on its Indigotin content level, the percentage by weight of actual pigment. Indigotin levels of quality dye concentrate almost always range between 10% and 50%.
The indigo pigment molecule is non-reactive in water. It cannot be dissolved (like salt for example), but it can and must be put into liquid suspension as a first step to making an Indigo vat. The majority of indigo extract in the market is synthetically produced from fossil fuel extracts, it is generally cheaper, though functionally nearly identical to indigo derived directly from plants. The most common form of natural indigo in the marketplace is concentrated pigment in finely ground powder form from the plant Indigofera tinctoria or related species. All processes that I’m describing here presume that is the dye product you’re working with. There are a wealth of other indigos out there, both natural and synthetic, most all of which you can treat similarly to this and get good results.
The indigo pigment molecule, as purchased, will not react with cloth or dye it. It can be rubbed in and will cause a temporary stain, but it is not dye. For the indigo to actually transfer and adhere with the cloth, we must create what is called a Vat. The Vat will be referred to with a capital V here, for at the scale of the individual dyer, the entity known as the Vat has an incredible amount of history and personage, requires pampering and sustenance, often warmth and food. The Vat serves to modify the Indigo molecule in such a way that it eschews inertness (as it tends to be when in blue-powder form) and chemically interacts with AKA dyes cloth (and other things, but for our purpose, cloth). The Vat must fulfill two conditions to properly modify the Indigo. The Vat must first have an elevated pH, a condition know as alkalinity in which the amount of OH− ions exceeds that of H+ ions in the solution. Second, the Vat must be a reduced solution, meaning (in this case specifically) that the solution is devoid of dissolved oxygen and there are an excess of electrons in solution which causes the oxygen atoms present on the indigo molecule to be reduced (essentially snatching up these electrons into their orbit) and changing the Indigo molecule into what is called Leuco-Indigo which becomes dissolved in the Vat solution. This change is easily visually confirmed! Leuco-Indigo will appear as a transparent yellow-green (not too dissimilar from a childhood favorite soda, Mountain Dew) as compared to the opaque dark blue of Indigotin in suspension.
This photograph displays the indigo molecule in multiple forms. The dark, opaque blue ‘flower’ that sits atop an indigo vat is oxidized indigo – a molecule that will not dye fabric. The leuco-indigo dissolved in the Vat is visible as a yellow-green liquid – this molecule has the ability to chemically bond to (dye!) many different materials.
Once we have a properly reduced, leuco-indigo rich Vat, we can dip our cloth to dye with indigo. At the moment that the cloth emerges from the Vat it will be colored a tinge of green with the reduced leuco-indigo. As the piece comes into contact with the atmosphere, the pigment molecule, now adhered to the fabric, will lose its excess electrons and visibly transition back to blue.
There are many different ways of creating a Vat! There are many paths that will get you to the same finished product, a beautifully dyed blue piece! Each Vat style requires different ingredients and maintenance, and each has a set of positive and negative attributes.
The single best source for information about different styles of indigo and different ways of producing a vat is this book by John Marshall
The simple recipe that I advocate for the beginner is one that fits with our modern world. It is easy to make, requires no upkeep and (if properly sealed between uses) can be used on-demand for months at a time until it is exhausted of pigment. It is know as The Iron Vat. I’ve outlined the pros and cons for working with the Iron Vat below. If you have questions about this or any other kind of vat, feel free to get in touch.
Indigo Leaf
Shepherd Textiles Indigo Leaf Natural Dye contains the raw dried leaves of the indigo plant, indigofera tinctoria. The leaves are very fresh—from either this year’s or last year’s harvest—and they have been only lightly crushed to the consistency of tea. As a result, they still contain the undamaged precursors of indigo blue, indican and beta-glucosidase. When the leaves are blended with ice water, the two precursors are combined and the chain reaction leading to indigo blue begins. Any protein fibers soaking in the cold water will be dyed beautiful shades of ice blue and turquoise as the reaction finishes. Please note that this method works on wool and silk, but not on cotton—use Indigo Extract instead. Our dried indigo leaf is grown in the USA and gives gorgeous ice blues on wool and silk at 100% weight-of-fabric.
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Background on Indigo Leaf
Natural indigo is extracted from the leaves of indigofera tinctoria, a short shrub that is a member of the legume family. Indigo is now cultivated world-wide, but is probably native to South Asia (Glowacki et al. 2012:542). It has been the most important source of blue dye for much of recorded history, and there is archaeological evidence that indigo was being used to dye fabric up to 4,000 years ago in India. Natural indigo was a major global commodity in the 18th and 19th centuries, and industries sprang up all across the world. It was one of the major exports of the antebellum U.S. South, especially around low-country South Carolina and Georgia, which have subtropical climates ideal for growing indigo. However, a German chemist identified the chemical structure of indigotin and discovered how to synthesize it in 1883 (ibid:542). This lead to the collapse of the indigo-growing industry. Today indigo is still the most important blue dye for clothing and jeans, but almost all of it is synthetically produced indigo, not indigo extracted from a plant.
Indigo is unique among all natural dyes in how it attaches to fiber. Boiling it in hot water will have no effect, because the blue coloring compound indigotin is insoluble in normal water. The traditional method of applying it involves fermenting the leaves, extracting the dyestuff, dissolving it in a reduction vat, and then dipping fabric in the vat. When fabric is removed from the vat, the dissolved indigotin oxidizes and comes back out of solution, bonding immediately to the fiber. However, it is possible to short-circuit this laborious process by taking advantage of the chemistry of indigo leaves.
Indigo does not exist in the plant in the form of blue indigotin—otherwise the plant itself would be blue. Instead, it exists in the form of two precursors, beta-glucosidase and indican. If the leaf is damaged by grazing herbivores or gnawed by insects, the precursors are mixed together and blue indigotin forms. This may have evolved as a defense mechanism against predation, although the evidence is unclear (Daykin 2011:5). If high-quality indigo leaves are harvested very carefully, the two precursors are preserved even after the leaves are dried. They can later be blended with ice water to mix the precursor compounds and begin the chemical reaction leading to blue indigotin. As the cold water warms up, the beta-glucosidase cleaves the indican into a molecule of indoxyl, and the indoxyl reacts with oxygen dissolved in the water to form blue indigotin. Any wool or silk soaking in the water while this reaction occurs will be dyed blue, too. Using fresh indigo leaves it is possible to achieve beautiful shades of turquoise and ice blue, without needing to build a reduction vat.
Nature’s Strongest Blue
