Indigo pigment is found in many plants around the world but unfortunately most of these plants are happiest in warmer climates than ours in New Jersey. Japanese indigo persicaria tinctoria, however, is easy to grow and readily reseeds in my zone 6 garden every year. I can usually get three cuttings in a summer before letting it go to seed in the fall. There are a few ways to use indigo, but the easiest methods are called fresh leaf and reduction vat.

The fresh leaf method works well on protein fibers and can be as simple as rubbing salt and fresh leaves through a silk scarf, or my preferred method of blending leaves with ice water and soaking wool or silk in the strained liquid for ten minute dips. As the water warms up it stops working so I will do a few batches to get deeper colors. Fresh leaf dyeing doesn’t give a true blue but gives a lovely blue-green.

Yarn dyed with fresh indigo

To make an indigo vat and get true blues I start with a water extraction. This involves cutting indigo stalks carefully so as not to bruise them and then soaking in water for about three days. I put bricks on the stalks to keep them submerged and put in a sunny spot on the driveway as heat speeds up the process.

Here you can see how the water has developed a bright blue-green antifreeze color.

At this point I remove the leaves and strain out all plant material -which often looks yellow and does not smell great! There is usually a metallic sheen on top of the water at this point.
The next step is to raise the pH to 10 or 11 by adding pickling lime (calcium hydroxide). I do this by dissolving the lime in hot water and then stirring it gradually in, testing pH frequently. The color will change and sometimes I’ll start to see blue pigment settling out of the water.

To get more of the pigment to settle out you need to aerate the solution. You can do this by pouring back and forth between two buckets or by using something to stir. I use a paddle attachment to a drill.

You want to get a nice blue foam before stopping:

Afterwards you must wait for the pigment to settle. I just cover it and leave it until the next day.
At this point you must decide if you want to strain out the pigment to save for later use or if you want to make a vat to dye right away. Straining requires patience as the pigment is easily disturbed. I try to scoop much of the excess water out into a bucket, and then strain the pigment through a coffee filter. Add vinegar to the discard water until the pH is neutral (7) then it can be dumped in the compost or down the drain.

This will leave a pudding textured pigment that I save in the refrigerator until needed. It can be dried to a powder instead but I find it easier to use already wet.

If you want to dye with freshly settled indigo pigment you can avoid straining and set up a vat. This just means you make sure the pH is between 10 and 11 and then add fructose. The usual ratio used in making a vat are 1 part dried indigo powder, 2 parts pickling lime and 3 parts fructose. When directly vatting you just have to guess how much fructose to use-which I usually base on how much pickling lime was required to get the pH to 11. I use 1.5 times that amount by weight

This is called creating a reduction vat because the fructose reduces the amount of oxygen in the water. Oxygen is what will turn the indigotin blue so you want that to happen on the fabric as it hits the air coming out of the vat not in the water. You don’t actually want to see blue water-a healthy indigo vat will look yellowish green or sometimes brownish green. It’s important not to splash or introduce oxygen into the vat when submerging fabric so I always make sure to soak things a half hour or more before starting dyeing with indigo. It usually takes several dips to get the depth of shade you’d like and the rule of thumb is to dye to a shade or two darker than you want the final color to be as some will come out in the first wash.

I always scour cotton fabrics with soda ash and/or cellulose scour in a pot on the stove before dyeing, but no mordant is needed. The scoured and wetted material can be stitched, pleated, or tied to create resist patterns before dyeing. You can place a rack in the bottom of the vat to keep fabric off the sediment on the bottom (optional) and soak for 5 to 20 minutes at a time. After lifting out the fabric let it drip and wring it out over another bucket so as not to disturb the vat too much. Then you’ll see the magic as fabric turns blue when the air hits it. Hang dyed fabrics for 10-20 minutes before dipping again. It can take 10 dips to get a very dark blue so patience is necessary. After the final dip I’ll do a quick rinse in water and sometimes a soak in 10% vinegar water if the fabric seems stiff. Then leave the dyed materials to dry and cure a day or so before washing. If you’d like more information on Indigo check out the tutorials on Botanicalcolors.com and the book Singing the Blues with John Marshall as Your 𝙂𝙪𝙞𝙙𝙚 .