Extracting indigo from frozen Japanese indigo plants at Okan Arts

indigo: extraction experiments

By Patricia Belyea

WAUCONDA WA  Where I left off in this story, we’d harvested our Japanese indigo crop after a record-breaking early frost. The leaves of our happy plants were dark and limp. Would the enzyme in the damaged indigo plants release its magical dye?

Experiment No. 1

We placed all 165 plants in a 140-gal tub filled with hot water. The plants were weighed down to keep them submerged. Using a tarp, we fashioned a make-shift covering over the tub and tucked a greenhouse heater under the tent-like structure.    

For three days, the water tested at 100 degrees. The plants decomposed and created a bubbly foam. Soon there was a shiny layer on the top of the water—not a fluorescent green but something similar to a rainbow oil slick.

We removed the plant matter and began the process of making the water basic by adding hydrated lime. The final addition of a little lime powder rose the pH to 11, a highly acceptable level. We whipped up the solution for twenty minutes with a mixing paddle on a drill. Then, we waited.

After a few days, a sludge settled on the bottom of the tub. We siphoned off the clear water with a battery-operated fuel pump. Our resulting mud was not an amazing royal blue. Instead, it was mid-brown with blue cast. Hmmmm.

Keeping the submerged indigo plants warm at Okan ArtsThe submerged indigo plants begin to bubble up in the warm water at Okan ArtsThe surface of the water with the submerged indigo plants gets shiny and greenishScum on surface of water filled with decomposed indigo plantsPatricia Belyea of Okan Arts removing spent indigo plants from the extraction tubpH test strips at Okan ArtsWhipping up the hydrated lime into the water of the indigo extraction vat at Okan ArtsBrown sludge created from Indigo Extraction Experiment No. 1 at Okan Arts

Experiment No. 2

Oh my goodness. When we looked at the discarded plants in the garden cart, the leaves were navy blue. Maybe the indigo was still in the plants!

The bulk of the plants was greatly decreased after decomposing in hot water for three days. We squeezed all the organic matter into two 20-gallon plastic bins filled with warm water, then weighted everything down with garden tiles.

After a week, a sheen emerged on the top of the water. It wasn't the desired color of antifreeze but it did look like an oil slick. We removed the plant matter and added hydrated lime in small increments until the solution reached a pH of 10. 

When everything settled, the sludge was again mid-brown—with hues of green in one bin and rose in another.

Partially decomposed indigo plants used in Indigo Extraction Experiment No. 2 at Okan ArtsExtracting indigo dye from frozen indigo plants at Okan Arts

Experiment No. 3

Talking with Bryan Whitehead in Fujino, Japan, he suggested a way to extract indigo from the sludge. He instructed me to: Mix together one cup of the greenish sludge with two gallons of water, and two cups of vinegar in a large pot. Boil down the mixture to cook off the slaked lime. Refill the liquids and repeat the boil-down process two more times. Dry the remaining residue on a cloth in the sun. The result—likely 1 ounce of pure indigo crystals.

I excitedly got to work making the concoction in a big canning pot. Twenty minutes into the process, boiling away on the stove in our kitchen, Michael asked me to stop. Although we have a good kitchen fan, Michael was concerned about us evaporating lime into our household air for 24 hours. It would probably not be good for our health.

I agreed and shut down the experiment. I reckoned that if I really needed natural indigo dye, I could buy some from Botanical Colors

Boiling off slaked lime in an indigo dye extraction experiment at Okan Arts


Right after we harvested the indigo crop, I was no longer walking down to our front field every morning. There was wet weather in our valley followed by a week of smoke from the West Coast fires. 

Three weeks after the emergency harvest, I was out in the field and noticed that most of the indigo plants were beginning to grow again! There were teeny leaves sprouting from the cut-off stalks.

Since it was going to freeze again that night, I got into action. I harvested all the leaves— 2.2 ounces of the minuscule leaves. Working with ice-cold water and a Ninja blender, I made a batch of fresh-leaf indigo dye.

I had three pieces of silk, each 1.3 ounces, ready to dye. The lengths of silk sat in the indigo bath for an hour and came out the palest shade of turquoise blue! Success, however meager!

Newly sprouted indigo leaves at Okan ArtsFor fresh leaf indigo dyeing: keeping a pile of minuscule indigo leaves cool on a damp tea towel on a bed of iceGetting everything ready for a fresh leaf indigo dye experiment at Okan ArtsFresh-leaf indigo dyeing at Okan ArtsFresh-leaf indigo dyeing at Okan ArtsFresh-leaf indigo dyeing at Okan Arts

With my fresh-leaf dye bath depleted, my indigo adventure was over. Well, almost. I still want to make a dye vat with my brown sludge and see what happens. More on that later. 

The best part of this experience was seeing tiny seeds burst into flourishing plants. Not being a gardener, let alone a farmer, this was all new for me.

I’m hooked. I definitely want to grow Japanese indigo again next summer. And, I plan to keep a very sharp eye on the weather reports!

Sludge from frost damaged indigo plants at Okan Arts

To read the story of growing and harvesting our indigo crop +click here