Glossary
Indigo: Indigo is a pigment from the leaves of the indigo plant called Indigofera tinctoria, one of the oldest dyes known to humankind. It is the only natural plant-based blue and its colorant is present in other plants, including woad (Isatis tinctoria), Japanese indigo, (Persicaria tinctoria, a buckwheat) and Strobilanthes cusia, a distant cousin to the ornamental Persian Shield that you can buy at Home Depot. Indigo was used to dye shrouds for Egyptian burials, uniforms for Napoleon’s Army, prestige cloth for African chiefs and to dye denim for blue jeans. Indigo was a valued historical crop and grown and tended by enslaved people in the US. European colonizers forced Bengali and indigenous workers to grow indigo under horrible conditions, resulting in worker uprisings and revolts. The color was synthesized around 1880 by Alfred Bayer and shortly after the world indigo market collapsed as manufacturers switched to the new miracle synthetic dye. Cultivation acreage plummeted and within 20 years only a fraction of the indigo used worldwide was from natural sources. An excellent resource about the history of indigo is Jenny Balfour-Paul’s book Indigo: Egyptian Mummies to Blue Jeans.
Grams per Liter (gpL): An expression used to determine the amount of indigo in a vat. The higher the gpL, the darker the vat will be.
Vat: The vat is the actual container of indigo and ingredients where you will dip your goods. The vat can be of varying sizes but a good rule of thumb is make it large enough so that your goods can move easily in the vat liquid, and be completely covered in the solution. The vat consists of room temperature or warm water and indigo stock solution.
Reduction: Indigo works differently than other natural dyes. Most other dyes require you to extract the dyestuff from the raw material by making a “tea” of dyestuff and liquid, or dissolving already extracted dyes in powder form with water, adding mordanted fibers and then simmering until the color has transferred to the fibers. The color bond between the mordanted fibers and the dyestuff is a chemical bond. Indigo requires that excess oxygen is removed from the vat liquid, which makes the indigo color molecule available to physically attach to fiber. When the fiber is immersed in the vat, indigo attaches weakly to the fiber. The fiber in the vat is not blue at this time. It’s yellow-green, and scientists call this “indigo white” or “leuco indigo”.
Oxidation: Oxidation is when the indigo fiber is removed from the vat. Oxygen in the air reconverts the weakly attached indigo and allows it to attach to the fiber, forming a stronger bond and allowing the blue color to emerge. This is the magic you see when the yellow-green fiber slowly changes to blue before your eyes.
Reducing Agent: This is the chemical that will remove excess oxygen in your vat, allowing your vat to balance and become available for dipping. Common reducing agents are fructose (fruit sugar), henna powder, iron and used madder roots.
pH: The indigo vat is dependent upon a moderately high pH level between 10 and 11.5 for cellulose fibers. This pH level is moderated by calcium hydroxide. If your pH is too low, the chemical reaction in your vat will not be efficient and may affect the color. To raise pH, add a small amount of calcium hydroxide to the vat, stir and wait for the vat to balance. If the pH is too high, add a mild acid such as distilled white vinegar. Measure pH with our pH indicator strips.
Over-reduced Vat: An over-reduced vat is when you have added too much reducing agent. Add air into the vat with vigorous stirring to rebalance. It’s fairly common to over-reduce a vat if using an industrial reducing agent such as thiourea dioxide (thiox) or sodium hydrosulfite (hydros) but less common when using fructose or henna.
Under-reduced Vat: An under-reduced vat is dark blue. If the vat is turning blue-colored, add more reducing agent and wait until the vat balances, clears and turns yellow-green or golden brown. If it doesn’t balance within 30 minutes, check the pH.
Layering: Indigo is considered a “layered” dye, meaning that it’s best the build the color with several dips rather than to dip once. Multiple dips are important to quality indigo dyeing and to reduce excessive dye rub off. Each dip allows more indigo to attach to the fiber, deepening the color.
FAQ
Selecting and Preparing Fibers
Indigo will dye nearly any natural fiber, including cotton, linen, hemp, bamboo, Tencel, Modal, viscose, rayon and blends. For animal fibers, indigo dyes wool, silk and other animal fibers beautifully. Natural fiber blends also dye well.
Polyester, microfiber and acrylic will not dye with indigo. Nylon can take some indigo dye as its structure mimics silk.
Tagua or corozo nut buttons also dye well with indigo. Plastic, shell, wood and pearl buttons do not dye well.
Basketry materials with non-porous surfaces are difficult to dye. Raffia and other softer materials are easier to dye.
Most natural fiber garments will dye well with indigo. Polyester blends will dye lighter, and polyester threads will not dye at all with indigo.
Mordanting for Indigo?
Indigo does not require a mordant, but the fabrics or fibers should be clean and wetted out.
Creating the Indigo Vat
Q: What size container should I use for the vat?
A: Use a container large enough for goods to move freely. One very common error is to make a vat that is too small for the goods you want to dip. A 5-gallon container is great for bandanas, short-sleeved t-shirts or tank tops, hats, sock and other smaller items. It is more difficult to dip larger items like denim or jackets in a 5-gallon vat.
Q:How much water should be in my vat?
A: Enough for your goods to move freely. We like to build a vat of about 16 quarts (4 gallons) in a 5-gallon container that provides enough space to dip the goods without overflowing the vat.
Q: Do I have to heat my vat? What if I don’t have a bucket heater?
A: We like to warm our vat before dipping, but if you don’t have a bucket heater, this can be a challenge. A handy tip that Sara Goodman of Sanborn Mills Farm told me was to scoop out about 3-4 quarts of the indigo stock and heat it on a stove top to about 140 F. Watch it carefully so it doesn’t boil. Then incorporate the heated liquid back into the indigo vat. This will raise the temperature to about 80 or 85 F and warm the rest of the vat liquid. Allow the vat to settle and reduce before dipping.
Q: Do I have to keep my vat warm to encourage fermentation?
A: 1-2-3 vats are not fermentation vats, although they can sometimes grow a layer of mold if left undisturbed for a long time. You do not need to keep your vat warm past the time that you are using the vat. We warm the vat to kickstart for future dips.
Dipping
How long should I dip?
hade darker tan th fureshe,Dipping times are dependent on the final shade. Light colors take fewer and shorter dips in vats with less indigo in them. Dark colors take longer dips.You can start with a 2 minute dip then let your goods oxidize. Evaluate the color and decide how many more dips. Remember that when you wash and dry the fiber, the color will be 1-2 shades lighter and we recommend dipping one
How do I keep my fabric from touching the sediment at the bottom of my vat?
The best way to avoid dragging your fabric or yarn through the sediment that collects at the bottom of a 1-2-3 vat is to suspend a colander or strainer in your vat. Then dip, and keep the fabric gently rotating while you are dipping. If you do pick up some sediment on your fabric, you can quickly dip the fabric into some water to wash the sediment away. If you are a yarn dyer, you can suspend your skein over the vat using a dowel and our yarn rings. The rings allow the yarn to stay in the vat and you can easily rotate them. If you have extra long skeins, you can double them and shorten them so they stay away from the bottom sediment.
Oxidization
How can I tell when it’s oxidized?
Oxidation is complete when the entire piece has turned blue. Check the hems of garments and inside wet skeins for complete oxidation. If you have a folded shibori piece, make sure the interior layers are oxidized by carefully separating them while oxidizing. Do not undo clamps or binding.
How long will my vat last?
Indigo vats can last a long time. We’ve revived and maintained both henna and fructose vats for many months. Some dyers have kept their vats going for years.
How do I revive or rebalance my vat?
If you use the 1-2-3 vat, you can re-balance it with more indigo, calcium hydroxide and fructose. It also helps to stir up the sediment at the bottom to incorporate the undissolved indigo. With other types of vats, check the pH and add alkali and a reducing agent and wait for the vat to balance.
I am no longer getting any color from my vat, do I throw it out?
If your vat is yielding lighter and lighter indigo shades, you can easily recharge it. You can add more indigo, calcium hydroxide and fructose/henna/iron in the 1-2-3 ratios, then stir the vat well, let it rest and once it’s settled, dip a test strip.
Overdyeing with Indigo
Can I overdye indigo with other natural dyes?
The best way to get clear over-dye colors when using indigo is to scour fabric, dye indigo, then mordant and over-dye with natural dyes. It seems counter-intuitive, and you need to practice a bit to understand what depth of indigo blue will create what over-dyed color, but it sharpens your color blending skills.