Frequently Asked Questions About Indigo


IndigoIndigo 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.

Indigo Stock Solution (also called a Starter or Mother): Indigo is dependent on a balanced blend of indigo powder, a base or alkali such as calcium hydroxide, and a reducing agent, such as fructose or henna. We have found it easier to build a vat if you mix these ingredients in a smaller container and let them react. Once the reaction is ready, then carefully add this stock solution to a container of water to create the vat. You can also create an indigo vat using the gpL method that we detail in our How To section to better control the amount of indigo and the resultant shade.

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 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 blue. If the vat is turning teal or 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.

Gloved hands lowering a white piece of fabric into an indigo vat
Detailed instructions for the 1-2-3 fructose vat may be found here.

Creating the Stock Solution

What size jar should I use to make the stock solution?

If you are creating a vat using 1-2 tablespoons of indigo, a quart jar is usually sufficient. If you are creating a vat using larger amounts of indigo, then you will need a larger vessel to mix the ingredients. You need enough water so the stock is the consistency of thin broth.

How much indigo should I use?

A rounded tablespoon of indigo weighs approx. 6 grams, which is enough to dye about 200 grams, roughly 7 oz or 2 small t-shirts a medium dark color with 2, 5 minute dips. 

Are the measurements 1-2-3 parts in weight or fluid ounces?

It’s a pretty flexible recipe. Many dyers don’t use weights and we’ve found it works fine with volume measurements as well as weight.

My stock turned very thick like mud. What do I do?

Add it to a larger jar or bucket and gradually stir in enough warm water so the consistency is like broth. Continue with the process to allow the chemical reaction to take place. 

How long can I save the stock solution?

Stock may be kept for weeks to months in a cool dark place. A tightly covered jar works best. Make sure you label it.

Creating the Indigo Vat

What size container should I use for the vat?

Use a container large enough for goods to move freely. 

How much water should be in my vat?

Enough for your goods to move freely.

Do I have to heat my vat?

A warm vat will assist with the chemical reaction. Start your vat with hot tap water if possible. We like to have our vat around 100-110F, or 37-43C. It is possible to have your vat at a cooler temperature but the reactions may take a little longer. If your vat is in a bucket, you can place it in a water bath and heat it gently.


How long should I dip?

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 5 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.

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 overturn a colander or strainer and place it on the bottom of 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.


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.

Can I oxidize in the sun?

We usually oxidize in the shade but I don’t believe there is a difference as sunlight should not affect the oxidation process.

blue yarn over an indigo vat in a white bucket

Maintaining the Vat

How long can I save the dye vat?

Indigo vats may be kept for several weeks or months in a cool dark place, but need to be re-balanced prior to dipping. Some dyers have kept their vats for years. If the amount of sediment at the bottom of the vat becomes bothersome, carefully remove some of it and discard, stir and rebalance the vat. Keep the vat covered with a tight-fitting lid when not in use. 

How do I rebalance my vat?

If you use the 1-2-3 vat, you can re-balance it with 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?

The vat may be maintained for several dipping sessions. Add more ingredients using the same 1-2-3 recipe and continue dipping. Assume that one tablespoon of indigo will dye about a half pound of fabric to a dark shade.

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.